Spring framework
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This document provides an overview and tutorial on the Spring Framework. It discusses that Spring is an open source Java platform that makes Java enterprise application development easier and faster. It was created by Rod Johnson in 2003. The document then covers Spring Framework concepts like dependency injection, aspect oriented programming, the various Spring modules for different applications, and how to set up a development environment for Spring.
![•org.springframework.beans-3.1.0.M2
•org.springframework.context.support-3.1.0.M2
•org.springframework.context-3.1.0.M2
•org.springframework.core-3.1.0.M2
•org.springframework.expression-3.1.0.M2
•commons-logging-1.1.1
Step 3 - Create Source Files:
Now let us create actual source files under the HelloSpring project. First we need to create a package
called com.tutorialspoint. To do this, right click on src in package explorer section and follow the option : New ->
Package.
Next we will create HelloWorld.java and MainApp.java files under the com.tutorialspoint package.
Here is the content of HelloWorld.java file:
package com.tutorialspoint;
public class HelloWorld {
private String message;
public void setMessage(String message){
this.message = message;
}
public void getMessage(){
System.out.println("Your Message : " + message);
}
}
Following is the content of the second file MainApp.java:
package com.tutorialspoint;
import org.springframework.context.ApplicationContext;
import org.springframework.context.support.ClassPathXmlApplicationContext;
public class MainApp {
public static void main(String[] args) {
ApplicationContext context =
new ClassPathXmlApplicationContext("Beans.xml");
HelloWorld obj = (HelloWorld) context.getBean("helloWorld");
obj.getMessage();
}
}
There are following two important points to note about the main program:
1.First step is to create application context where we used framework APIClassPathXmlApplicationContext(). This
API loads beans configuration file and eventually based on the provided API, it takes care of creating and initializing all
the objects ie. beans mentioned in the configuration file.
2.Second step is used to get required bean using getBean() method of the created context. This method uses bean ID
to return a generic object which finally can be casted to actual object. Once you have object, you can use this object to
call any class method.
Step 4 - Create Bean Configuration File:
You need to create a Bean Configuration file which is an XML file and acts as cement that glues the beans ie. classes
together. This file needs to be created under the src directory as shown below:](https://image.slidesharecdn.com/springframework-140424232629-phpapp01/85/Spring-framework-6-320.jpg)
![Ste
p
Description
1
Create a project with a name SpringExample and create a package com.tutorialspoint under
the src folder in the created project.
2
Add required Spring libraries using Add External JARs option as explained in the Spring
Hello World Example chapter.
3 Create Java classes HelloWorld and MainApp under the com.tutorialspoint package.
4 Create Beans configuration file Beans.xml under the src folder.
5
The final step is to create the content of all the Java files and Bean Configuration file and
run the application as explained below.
Here is the content of HelloWorld.java file:
package com.tutorialspoint;
public class HelloWorld {
private String message;
public void setMessage(String message){
this.message = message;
}
public void getMessage(){
System.out.println("Your Message : " + message);
}
}
Following is the content of the MainApp.java file:
package com.tutorialspoint;
import org.springframework.context.ApplicationContext;
import org.springframework.context.support.ClassPathXmlApplicationContext;
public class MainApp {
public static void main(String[] args) {
ApplicationContext context =
new ClassPathXmlApplicationContext("Beans.xml");
HelloWorld objA = (HelloWorld) context.getBean("helloWorld");
objA.setMessage("I'm object A");
objA.getMessage();
HelloWorld objB = (HelloWorld) context.getBean("helloWorld");
objB.getMessage();
}
}
Following is the configuration file Beans.xml required for singleton scope:
<?xml version="1.0" encoding="UTF-8"?>
<beans xmlns="http://www.springframework.org/schema/beans"
xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xsi:schemaLocation="http://www.springframework.org/schema/beans
http://www.springframework.org/schema/beans/spring-beans-3.0.xsd">
<bean id="helloWorld" class="com.tutorialspoint.HelloWorld"
scope="singleton">
</bean>
</beans>
Once you are done with creating source and bean configuration files, let us run the application. If everything is fine with
your application, this will print the following message:](https://image.slidesharecdn.com/springframework-140424232629-phpapp01/85/Spring-framework-11-320.jpg)
![Your Message : I'm object A
Your Message : I'm object A
The prototype scope:
If scope is set to prototype, the Spring IoC container creates new bean instance of the object every time a request for that
specific bean is made. As a rule, use the prototype scope for all state-full beans and the singleton scope for stateless
beans.
To define a prototype scope, you can set the scope property to prototype in the bean configuration file, as shown
below:
<!-- A bean definition with singleton scope -->
<bean id="..." class="..." scope="prototype">
<!-- collaborators and configuration for this bean go here -->
</bean>
EXAMPLE:
Let us have working Eclipse IDE in place and follow the following steps to create a Spring application:
Ste
p
Description
1
Create a project with a name SpringExample and create a package com.tutorialspoint under
the src folder in the created project.
2
Add required Spring libraries using Add External JARs option as explained in the Spring
Hello World Example chapter.
3 Create Java classes HelloWorld and MainApp under the com.tutorialspoint package.
4 Create Beans configuration file Beans.xml under the src folder.
5
The final step is to create the content of all the Java files and Bean Configuration file and
run the application as explained below.
Here is the content of HelloWorld.java file:
package com.tutorialspoint;
public class HelloWorld {
private String message;
public void setMessage(String message){
this.message = message;
}
public void getMessage(){
System.out.println("Your Message : " + message);
}
}
Following is the content of the MainApp.java file:
package com.tutorialspoint;
import org.springframework.context.ApplicationContext;
import org.springframework.context.support.ClassPathXmlApplicationContext;
public class MainApp {
public static void main(String[] args) {
ApplicationContext context =
new ClassPathXmlApplicationContext("Beans.xml");
HelloWorld objA = (HelloWorld) context.getBean("helloWorld");
objA.setMessage("I'm object A");
objA.getMessage();
HelloWorld objB = (HelloWorld) context.getBean("helloWorld");](https://image.slidesharecdn.com/springframework-140424232629-phpapp01/85/Spring-framework-12-320.jpg)
![public class MainApp {
public static void main(String[] args) {
AbstractApplicationContext context =
new ClassPathXmlApplicationContext("Beans.xml");
HelloWorld obj = (HelloWorld) context.getBean("helloWorld");
obj.getMessage();
context.registerShutdownHook();
}
}
Following is the configuration file Beans.xml required for init and destroy methods:
<?xml version="1.0" encoding="UTF-8"?>
<beans xmlns="http://www.springframework.org/schema/beans"
xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xsi:schemaLocation="http://www.springframework.org/schema/beans
http://www.springframework.org/schema/beans/spring-beans-3.0.xsd">
<bean id="helloWorld"
class="com.tutorialspoint.HelloWorld"
init-method="init" destroy-method="destroy">
<property name="message" value="Hello World!"/>
</bean>
</beans>
Once you are done with creating source and bean configuration files, let us run the application. If everything is fine with
your application, this will print the following message:
Bean is going through init.
Your Message : Hello World!
Bean will destroy now.
Default initialization and destroy methods:
If you have too many beans having initialization and or destroy methods with the same name, you don't need to
declare init-method and destroy-method on each individual bean. Instead framework provides the flexibility to
configure such situation using default-init-method and default-destroy-methodattributes on the <beans> element
as follows:
<beans xmlns="http://www.springframework.org/schema/beans"
xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xsi:schemaLocation="http://www.springframework.org/schema/beans
http://www.springframework.org/schema/beans/spring-beans-3.0.xsd"
default-init-method="init"
default-destroy-method="destroy">
<bean id="..." class="...">
<!-- collaborators and configuration for this bean go here -->
</bean>
</beans>](https://image.slidesharecdn.com/springframework-140424232629-phpapp01/85/Spring-framework-15-320.jpg)
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Spring framework
- 1. Spring Framework Tutorial Spring framework is an open source Java platform that provides comprehensive infrastructure support for developing robust Java applications very easily and very rapidly. Spring framework was initially written by Rod Johnson and was first released under the Apache 2.0 license in June 2003. This tutorial has been written based on Spring Framework version 3.1.0 released in Dec 2011. Spring Framework Overview Spring is the most popular application development framework for enterprise Java. Millions of developers around the world use Spring Framework to create high performing, easily testable, reusable code. Spring framework is an open source Java platform and it was initially written by Rod Johnson and was first released under the Apache 2.0 license in June 2003. Spring is lightweight when it comes to size and transparency. The basic version of spring framework is around 2MB. The core features of the Spring Framework can be used in developing any Java application, but there are extensions for building web applications on top of the Java EE platform. Spring framework targets to make J2EE development easier to use and promote good programming practice by enabling a POJO-based programming model. Benefits of Using Spring Framework: Following is the list of few of the great benefits of using Spring Framework: •Spring enables developers to develop enterprise-class applications using POJOs. The benefit of using only POJOs is that you do not need an EJB container product such as an application server but you have the option of using only a robust servlet container such as Tomcat or some commercial product. •Spring is organized in a modular fashion. Even though the number of packages and classes are substantial, you have to worry only about ones you need and ignore the rest. •Spring does not reinvent the wheel instead, it truly makes use of some of the existing technologies like several ORM frameworks, logging frameworks, JEE, Quartz and JDK timers, other view technologies. •Testing an application written with Spring is simple because environment-dependent code is moved into this framework. Furthermore, by using JavaBean-style POJOs, it becomes easier to use dependency injection for injecting test data. •Spring's web framework is a well-designed web MVC framework, which provides a great alternative to web frameworks such as Struts or other over engineered or less popular web frameworks. •Spring provides a convenient API to translate technology-specific exceptions (thrown by JDBC, Hibernate, or JDO, for example) into consistent, unchecked exceptions. •Lightweight IoC containers tend to be lightweight, especially when compared to EJB containers, for example. This is beneficial for developing and deploying applications on computers with limited memory and CPU resources. •Spring provides a consistent transaction management interface that can scale down to a local transaction (using a single database, for example) and scale up to global transactions (using JTA, for example). Dependency Injection (DI): The technology that Spring is most identified with is the Dependency Injection (DI) flavor of Inversion of Control. The Inversion of Control (IoC) is a general concept, and it can be expressed in many different ways and Dependency Injection is merely one concrete example of Inversion of Control. When writing a complex Java application, application classes should be as independent as possible of other Java classes to increase the possibility to reuse these classes and to test them independently of other classes while doing unit testing. Dependency Injection helps in gluing these classes together and same time keeping them independent. What is dependency injection exactly? Let's look at these two words separately. Here the dependency part translates into an association between two classes. For example, class A is dependent on class B. Now, let's look at the second part, injection. All this means is that class B will get injected into class A by the IoC. Dependency injection can happen in the way of passing parameters to the constructor or by post-construction using setter methods. As Dependency Injection is the heart of Spring Framework, so I will explain this concept in a separate chapter with a nice example. Aspect Oriented Programming (AOP): One of the key components of Spring is the Aspect oriented programming (AOP) framework. The functions that span multiple points of an application are called cross-cutting concerns and these cross-cutting concerns are conceptually separate from the application's business logic. There are various common good examples of aspects including logging, declarative transactions, security, and caching etc. The key unit of modularity in OOP is the class, whereas in AOP the unit of modularity is the aspect. Whereas DI helps
- 2. you decouple your application objects from each other, AOP helps you decouple cross-cutting concerns from the objects that they affect. The AOP module of Spring Framework provides aspect-oriented programming implementation allowing you to define method-interceptors and pointcuts to cleanly decouple code that implements functionality that should be separated. Spring Framework Tutorial Spring could potentially be a one-stop shop for all your enterprise applications, however, Spring is modular, allowing you to pick and choose which modules are applicable to you, without having to bring in the rest. Following section gives detail about all the modules available in Spring Framework. The Spring Framework provides about 20 modules which can be used based on an application requirement. Core Container: The Core Container consists of the Core, Beans, Context, and Expression Language modules whose detail is as follows: •The Core module provides the fundamental parts of the framework, including the IoC and Dependency Injection features. •The Bean module provides BeanFactory which is a sophisticated implementation of the factory pattern. •The Context module builds on the solid base provided by the Core and Beans modules and it is a medium to access any objects defined and configured. The ApplicationContext interface is the focal point of the Context module. •The Expression Language module provides a powerful expression language for querying and manipulating an object graph at runtime. Data Access/Integration: The Data Access/Integration layer consists of the JDBC, ORM, OXM, JMS and Transaction modules whose detail is as follows: •The JDBC module provides a JDBC-abstraction layer that removes the need to do tedious JDBC related coding. •The ORM module provides integration layers for popular object-relational mapping APIs, including JPA, JDO, Hibernate, and iBatis. •The OXM module provides an abstraction layer that supports Object/XML mapping implementations for JAXB, Castor, XMLBeans, JiBX and XStream. •The Java Messaging Service JMS module contains features for producing and consuming messages. •The Transaction module supports programmatic and declarative transaction management for classes that implement special interfaces and for all your POJOs.
- 3. Web: The Web layer consists of the Web, Web-Servlet, Web-Struts, and Web-Portlet modules whose detail is as follows: •The Web module provides basic web-oriented integration features such as multipart file-upload functionality and the initialization of the IoC container using servlet listeners and a web-oriented application context. •The Web-Servlet module contains Spring's model-view-controller (MVC) implementation for web applications. •The Web-Struts module contains the support classes for integrating a classic Struts web tier within a Spring application. •The Web-Portlet module provides the MVC implementation to be used in a portlet environment and mirrors the functionality of Web-Servlet module. Miscellaneous: There are few other important modules like AOP, Aspects, Instrumentation, Web and Test modules whose detail is as follows: •The AOP module provides aspect-oriented programming implementation allowing you to define method-interceptors and pointcuts to cleanly decouple code that implements functionality that should be separated. •The Aspects module provides integration with AspectJ which is again a powerful and mature aspect oriented programming (AOP) framework. •The Instrumentation module provides class instrumentation support and class loader implementations to be used in certain application servers. •The Test module supports the testing of Spring components with JUnit or TestNG frameworks. Spring Environment Setup This tutorial will guide you on how to prepare a development environment to start your work with Spring Framework. This tutorial will also teach you how to setup JDK, Tomcat and Eclipse on your machine before you setup Spring Framework: Step 1 - Setup Java Development Kit (JDK): You can download the latest version of SDK from Oracle's Java site: Java SE Downloads. You will find instructions for installing JDK in downloaded files, follow the given instructions to install and configure the setup. Finally set PATH and JAVA_HOME environment variables to refer to the directory that contains java and javac, typically java_install_dir/bin and java_install_dir respectively. If you are running Windows and installed the JDK in C:jdk1.6.0_15, you would have to put the following line in your C:autoexec.bat file. set PATH=C:jdk1.6.0_15bin;%PATH% set JAVA_HOME=C:jdk1.6.0_15 Alternatively, on Windows NT/2000/XP, you could also right-click on My Computer, select Properties, then Advanced, then Environment Variables. Then, you would update the PATH value and press the OK button. On Unix (Solaris, Linux, etc.), if the SDK is installed in /usr/local/jdk1.6.0_15 and you use the C shell, you would put the following into your .cshrc file. setenv PATH /usr/local/jdk1.6.0_15/bin:$PATH setenv JAVA_HOME /usr/local/jdk1.6.0_15 Alternatively, if you use an Integrated Development Environment (IDE) like Borland JBuilder, Eclipse, IntelliJ IDEA, or Sun ONE Studio, compile and run a simple program to confirm that the IDE knows where you installed Java, otherwise do proper setup as given document of the IDE. Step 2 - Install Apache Common Logging API: You can download the latest version of Apache Commons Logging API fromhttp://commons.apache.org/logging/. Once you downloaded the installation, unpack the binary distribution into a convenient location. For example in C:commons- logging-1.1.1 on windows, or /usr/local/commons-logging-1.1.1 on Linux/Unix. This directory will have following jar files and other supporting documents etc.
- 4. Make sure you set your CLASSPATH variable on this directory properly otherwise you will face problem while running your application. Step 3 - Setup Eclipse IDE All the examples in this tutorial have been written using Eclipse IDE. So I would suggest you should have latest version of Eclipse installed on your machine. To install Eclipse IDE, download the latest Eclipse binaries from http://www.eclipse.org/downloads/. Once you downloaded the installation, unpack the binary distribution into a convenient location. For example in C:eclipse on windows, or /usr/local/eclipse on Linux/Unix and finally set PATH variable appropriately. Eclipse can be started by executing the following commands on windows machine, or you can simply double click on eclipse.exe %C:eclipseeclipse.exe Eclipse can be started by executing the following commands on Unix (Solaris, Linux, etc.) machine: $/usr/local/eclipse/eclipse After a successful startup, if everything is fine then it should display following result:
- 5. Step 4 - Setup Spring Framework Libraries Now if everything is fine, then you can proceed to setup your Spring framework. Following are the simple steps to download and install the framework on your machine. •Make a choice whether you want to install Spring on Windows, or Unix and then proceed to the next step to download .zip file for windows and .tz file for Unix. •Download the latest version of Spring framework binaries fromhttp://www.springsource.org/download. •At the time of writing this tutorial, I downloaded spring-framework-3.1.0.M2.zip on my Windows machine and when you unzip the downloaded file it will give you directory structure inside C:spring-framework-3.1.0.M2 as follows. You will find all the Spring libraries in the directory C:spring-framework-3.1.0.M2dist. Make sure you set your CLASSPATH variable on this directory properly otherwise you will face problem while running your application. If you are using Eclipse then it is not required to set CLASSPATH because all the setting will be done through Eclipse. Once you are done with this last step, you are ready to proceed for your first Spring Example Spring Hello World Example Advertisements Previous Page Next Page Let us start actual programming with Spring Framework. Before you start writing your first example using Spring framework, you have to make sure that you have setup your Spring environment properly as explained in Spring - Environment Setup tutorial. I also assume that you have a little bit working knowledge with Eclipse IDE. So let us proceed to write a simple Spring Application which will print "Hello World!" or any other message based on the configuration done in Spring Beans Configuration file. Step 1 - Create Java Project: The first step is to create a simple Java Project using Eclipse IDE. Follow the option File -> New -> Project and finally select Java Project wizard from the wizard list. Now name your project asHelloSpring using the wizard window as follows: Once your project is created successfully, you will have following content in your Project Explorer: Step 2 - Add Required Libraries: As a second step let us add Spring Framework and common logging API libraries in our project. To do this, right click on your project name HelloSpring and then follow the following option available in context menu: Build Path -> Configure Build Path to display the Java Build Path window as follows: Now use Add External JARs button available under Libraries tab to add the following core JARs from Spring Framework and Common Logging installation directories: •antlr-runtime-3.0.1 •org.springframework.aop-3.1.0.M2 •org.springframework.asm-3.1.0.M2 •org.springframework.aspects-3.1.0.M2
- 6. •org.springframework.beans-3.1.0.M2 •org.springframework.context.support-3.1.0.M2 •org.springframework.context-3.1.0.M2 •org.springframework.core-3.1.0.M2 •org.springframework.expression-3.1.0.M2 •commons-logging-1.1.1 Step 3 - Create Source Files: Now let us create actual source files under the HelloSpring project. First we need to create a package called com.tutorialspoint. To do this, right click on src in package explorer section and follow the option : New -> Package. Next we will create HelloWorld.java and MainApp.java files under the com.tutorialspoint package. Here is the content of HelloWorld.java file: package com.tutorialspoint; public class HelloWorld { private String message; public void setMessage(String message){ this.message = message; } public void getMessage(){ System.out.println("Your Message : " + message); } } Following is the content of the second file MainApp.java: package com.tutorialspoint; import org.springframework.context.ApplicationContext; import org.springframework.context.support.ClassPathXmlApplicationContext; public class MainApp { public static void main(String[] args) { ApplicationContext context = new ClassPathXmlApplicationContext("Beans.xml"); HelloWorld obj = (HelloWorld) context.getBean("helloWorld"); obj.getMessage(); } } There are following two important points to note about the main program: 1.First step is to create application context where we used framework APIClassPathXmlApplicationContext(). This API loads beans configuration file and eventually based on the provided API, it takes care of creating and initializing all the objects ie. beans mentioned in the configuration file. 2.Second step is used to get required bean using getBean() method of the created context. This method uses bean ID to return a generic object which finally can be casted to actual object. Once you have object, you can use this object to call any class method. Step 4 - Create Bean Configuration File: You need to create a Bean Configuration file which is an XML file and acts as cement that glues the beans ie. classes together. This file needs to be created under the src directory as shown below:
- 7. Usually developers keep this file name as Beans.xml, but you are independent to choose any name you like. You have to make sure that this file is available in CLASSPATH and use the same name in main application while creating application context as shown in MainApp.java file. The Beans.xml is used to assign unique IDs to different beans and to control the creation of objects with different values without impacting any of the Spring source files. For example, using below file you can pass any value for "message" variable and so you can print different values of message without impacting HelloWorld.java and MainApp.java files. Let us see how it works: <?xml version="1.0" encoding="UTF-8"?> <beans xmlns="http://www.springframework.org/schema/beans" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:schemaLocation="http://www.springframework.org/schema/beans http://www.springframework.org/schema/beans/spring-beans-3.0.xsd"> <bean id="helloWorld" class="com.tutorialspoint.HelloWorld"> <property name="message" value="Hello World!"/> </bean> </beans> When Spring application gets loaded into the memory, Framework makes use of the above configuration file to create all the beans defined and assign them a unique ID as defined in <bean>tag. You can use <property> tag to pass the values of different variables used at the time of object creation. Step 5 - Running the Program: Once you are done with creating source and beans configuration files, you are ready for this step which is compiling and running your program. To do this, Keep MainApp.Java file tab active and use eitherRun option available in the Eclipse IDE or use Ctrl + F11 to compile and run your MainApp application. If everything is fine with your application, this will print the following message in Eclipse IDE's console: Your Message : Hello World! Congratulations, you have created your first Spring Application successfully. You can see the flexibility of above Spring application by changing the value of "message" property and keeping both the source files unchanged. Spring IoC Containers The Spring container is at the core of the Spring Framework. The container will create the objects, wire them together, configure them, and manage their complete lifecycle from creation till destruction. The Spring container uses dependency
- 8. injection (DI) to manage the components that make up an application. These objects are called Spring Beans which we will discuss in next chapter. The container gets its instructions on what objects to instantiate, configure, and assemble by reading configuration metadata provided. The configuration metadata can be represented either by XML, Java annotations, or Java code. The following diagram is a high-level view of how Spring works. The Spring IoC container makes use of Java POJO classes and configuration metadata to produce a fully configured and executable system or application. Spring provides following two distinct types of containers. S. N. Container & Description 1 Spring BeanFactory Container This is the simplest container providing basic support for DI and defined by theorg.springframework.beans.factory.BeanFactory interface. The BeanFactory and related interfaces, such as BeanFactoryAware, InitializingBean, DisposableBean, are still present in Spring for the purposes of backward compatibility with the large number of third-party frameworks that integrate with Spring. 2 Spring ApplicationContext Container This container adds more enterprise-specific functionality such as the ability to resolve textual messages from a properties file and the ability to publish application events to interested event listeners. This container is defined by the org.springframework.context.ApplicationContextinterface. The ApplicationContext container includes all functionality of the BeanFactory container, so it is generally recommended over the BeanFactory. BeanFactory can still be used for light weight applications like mobile devices or applet based applications where data volume and speed is significant. Spring Bean Definition The objects that form the backbone of your application and that are managed by the Spring IoC container are called beans. A bean is an object that is instantiated, assembled, and otherwise managed by a Spring IoC container. These beans are created with the configuration metadata that you supply to the container, for example, in the form of XML <bean/> definitions which you have already seen in previous chapters. The bean definition contains the information called configuration metadata which is needed for the container to know the followings: •How to create a bean •Bean's lifecycle details
- 9. •Bean's dependencies All the above configuration metadata translates into a set of the following properties that make up each bean definition. Properties Description class This attribute is mandatory and specify the bean class to be used to create the bean. name This attribute specifies the bean identifier uniquely. In XML-based configuration metadata, you use the id and/or name attributes to specify the bean identifier(s). scope This attribute specifies the scope of the objects created from a particular bean definition and it will be discussed in bean scopes chapter. constructor-arg This is used to inject the dependencies and will be discussed in next chapters. properties This is used to inject the dependencies and will be discussed in next chapters. autowiring mode This is used to inject the dependencies and will be discussed in next chapters. lazy-initialization mode A lazy-initialized bean tells the IoC container to create a bean instance when it is first requested, rather than at startup. initialization method A callback to be called just after all necessary properties on the bean have been set by the container. It will be discussed in bean life cycle chapter. destruction method A callback to be used when the container containing the bean is destroyed. It will be discussed in bean life cycle chapter. Spring Configuration Metadata Spring IoC container is totally decoupled from the format in which this configuration metadata is actually written. There are following three important methods to provide configuration metadata to the Spring Container: 1.XML based configuration file. 2.Annotation-based configuration 3.Java-based configuration You already have seen how XML based configuration metadata provided to the container, but let us see another sample of XML based configuration file with different bean definitions including lazy initialization, initialization method and destruction method: <?xml version="1.0" encoding="UTF-8"?> <beans xmlns="http://www.springframework.org/schema/beans" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:schemaLocation="http://www.springframework.org/schema/beans http://www.springframework.org/schema/beans/spring-beans-3.0.xsd"> <!-- A simple bean definition --> <bean id="..." class="..."> <!-- collaborators and configuration for this bean go here --> </bean> <!-- A bean definition with lazy init set on --> <bean id="..." class="..." lazy-init="true"> <!-- collaborators and configuration for this bean go here --> </bean> <!-- A bean definition with initialization method -->
- 10. <bean id="..." class="..." init-method="..."> <!-- collaborators and configuration for this bean go here --> </bean> <!-- A bean definition with destruction method --> <bean id="..." class="..." destroy-method="..."> <!-- collaborators and configuration for this bean go here --> </bean> <!-- more bean definitions go here --> </beans> You can check Spring Hello World Example to understand how to define, configure and create Spring Beans. I will discuss about Annotation Based Configuration in a separate chapter. I kept it intentionally in a separate chapter because I want you to grasp few other important Spring concepts before you start programming width Spring Dependency Injection with Annotations. Spring Bean Scopes When defining a <bean> in Spring, you have the option of declaring a scope for that bean. For example, To force Spring to produce a new bean instance each time one is needed, you should declare the bean's scope attribute to be prototype. Similar way if you want Spring to return the same bean instance each time one is needed, you should declare the bean's scope attribute to be singleton. The Spring Framework supports following five scopes, three of which are available only if you use a web-aware ApplicationContext. Scope Description singleton This scopes the bean definition to a single instance per Spring IoC container (default). prototype This scopes a single bean definition to have any number of object instances. request This scopes a bean definition to an HTTP request. Only valid in the context of a web-aware Spring ApplicationContext. session This scopes a bean definition to an HTTP session. Only valid in the context of a web-aware Spring ApplicationContext. global- session This scopes a bean definition to a global HTTP session. Only valid in the context of a web-aware Spring ApplicationContext. This chapter will discuss about first two scopes and remaining three will be discussed when we will discuss about web- aware Spring ApplicationContext. The singleton scope: If scope is set to singleton, the Spring IoC container creates exactly one instance of the object defined by that bean definition. This single instance is stored in a cache of such singleton beans, and all subsequent requests and references for that named bean return the cached object. The default scope is always singleton however, when you need one and only one instance of a bean, you can set the scope property to singleton in the bean configuration file, as shown below: <!-- A bean definition with singleton scope --> <bean id="..." class="..." scope="singleton"> <!-- collaborators and configuration for this bean go here --> </bean> EXAMPLE: Let us have working Eclipse IDE in place and follow the following steps to create a Spring application:
- 11. Ste p Description 1 Create a project with a name SpringExample and create a package com.tutorialspoint under the src folder in the created project. 2 Add required Spring libraries using Add External JARs option as explained in the Spring Hello World Example chapter. 3 Create Java classes HelloWorld and MainApp under the com.tutorialspoint package. 4 Create Beans configuration file Beans.xml under the src folder. 5 The final step is to create the content of all the Java files and Bean Configuration file and run the application as explained below. Here is the content of HelloWorld.java file: package com.tutorialspoint; public class HelloWorld { private String message; public void setMessage(String message){ this.message = message; } public void getMessage(){ System.out.println("Your Message : " + message); } } Following is the content of the MainApp.java file: package com.tutorialspoint; import org.springframework.context.ApplicationContext; import org.springframework.context.support.ClassPathXmlApplicationContext; public class MainApp { public static void main(String[] args) { ApplicationContext context = new ClassPathXmlApplicationContext("Beans.xml"); HelloWorld objA = (HelloWorld) context.getBean("helloWorld"); objA.setMessage("I'm object A"); objA.getMessage(); HelloWorld objB = (HelloWorld) context.getBean("helloWorld"); objB.getMessage(); } } Following is the configuration file Beans.xml required for singleton scope: <?xml version="1.0" encoding="UTF-8"?> <beans xmlns="http://www.springframework.org/schema/beans" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:schemaLocation="http://www.springframework.org/schema/beans http://www.springframework.org/schema/beans/spring-beans-3.0.xsd"> <bean id="helloWorld" class="com.tutorialspoint.HelloWorld" scope="singleton"> </bean> </beans> Once you are done with creating source and bean configuration files, let us run the application. If everything is fine with your application, this will print the following message:
- 12. Your Message : I'm object A Your Message : I'm object A The prototype scope: If scope is set to prototype, the Spring IoC container creates new bean instance of the object every time a request for that specific bean is made. As a rule, use the prototype scope for all state-full beans and the singleton scope for stateless beans. To define a prototype scope, you can set the scope property to prototype in the bean configuration file, as shown below: <!-- A bean definition with singleton scope --> <bean id="..." class="..." scope="prototype"> <!-- collaborators and configuration for this bean go here --> </bean> EXAMPLE: Let us have working Eclipse IDE in place and follow the following steps to create a Spring application: Ste p Description 1 Create a project with a name SpringExample and create a package com.tutorialspoint under the src folder in the created project. 2 Add required Spring libraries using Add External JARs option as explained in the Spring Hello World Example chapter. 3 Create Java classes HelloWorld and MainApp under the com.tutorialspoint package. 4 Create Beans configuration file Beans.xml under the src folder. 5 The final step is to create the content of all the Java files and Bean Configuration file and run the application as explained below. Here is the content of HelloWorld.java file: package com.tutorialspoint; public class HelloWorld { private String message; public void setMessage(String message){ this.message = message; } public void getMessage(){ System.out.println("Your Message : " + message); } } Following is the content of the MainApp.java file: package com.tutorialspoint; import org.springframework.context.ApplicationContext; import org.springframework.context.support.ClassPathXmlApplicationContext; public class MainApp { public static void main(String[] args) { ApplicationContext context = new ClassPathXmlApplicationContext("Beans.xml"); HelloWorld objA = (HelloWorld) context.getBean("helloWorld"); objA.setMessage("I'm object A"); objA.getMessage(); HelloWorld objB = (HelloWorld) context.getBean("helloWorld");
- 13. objB.getMessage(); } } Following is the configuration file Beans.xml required for prototype scope: <?xml version="1.0" encoding="UTF-8"?> <beans xmlns="http://www.springframework.org/schema/beans" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:schemaLocation="http://www.springframework.org/schema/beans http://www.springframework.org/schema/beans/spring-beans-3.0.xsd"> <bean id="helloWorld" class="com.tutorialspoint.HelloWorld" scope="prototype"> </bean> </beans> Once you are done with creating source and bean configuration files, let us run the application. If everything is fine with your application, this will print the following message: Your Message : I'm object A Your Message : null Spring Bean Life Cycle The life cycle of a Spring bean is easy to understand. When a bean is instantiated, it may be required to perform some initialization to get it into a usable state. Similarly, when the bean is no longer required and is removed from the container, some cleanup may be required. Though, there is lists of the activities that take place behind the scenes between the time of bean Instantiation and its destruction, but this chapter will discuss only two important bean lifecycle callback methods which are required at the time of bean initialization and its destruction. To define setup and teardown for a bean, we simply declare the <bean> with init-method and/ordestroy- method parameters. The init-method attribute specifies a method that is to be called on the bean immediately upon instantiation. Similarly, destroy-method specifies a method that is called just before a bean is removed from the container. Initialization callbacks: The org.springframework.beans.factory.InitializingBean interface specifies a single method: void afterPropertiesSet() throws Exception; So you can simply implement above interface and initialization work can be done inside afterPropertiesSet() method as follows: public class ExampleBean implements InitializingBean { public void afterPropertiesSet() { // do some initialization work } } In the case of XML-based configuration metadata, you can use the init-method attribute to specify the name of the method that has a void no-argument signature. For example: <bean id="exampleBean" class="examples.ExampleBean" init-method="init"/> Following is the class definition: public class ExampleBean { public void init() { // do some initialization work } } Destruction callbacks The org.springframework.beans.factory.DisposableBean interface specifies a single method: void destroy() throws Exception; So you can simply implement above interface and finalization work can be done inside destroy() method as follows: public class ExampleBean implements DisposableBean {
- 14. public void destroy() { // do some destruction work } } In the case of XML-based configuration metadata, you can use the destroy-method attribute to specify the name of the method that has a void no-argument signature. For example: <bean id="exampleBean" class="examples.ExampleBean" destroy-method="destroy"/> Following is the class definition: public class ExampleBean { public void destroy() { // do some destruction work } } If you are using Spring's IoC container in a non-web application environment; for example, in a rich client desktop environment; you register a shutdown hook with the JVM. Doing so ensures a graceful shutdown and calls the relevant destroy methods on your singleton beans so that all resources are released. It is recommended that you do not use the InitializingBean or DisposableBean callbacks, because XML configuration gives much flexibility in terms of naming your method. Example: Let us have working Eclipse IDE in place and follow the following steps to create a Spring application: Ste p Description 1 Create a project with a name SpringExample and create a package com.tutorialspoint under the src folder in the created project. 2 Add required Spring libraries using Add External JARs option as explained in the Spring Hello World Example chapter. 3 Create Java classes HelloWorld and MainApp under the com.tutorialspoint package. 4 Create Beans configuration file Beans.xml under the src folder. 5 The final step is to create the content of all the Java files and Bean Configuration file and run the application as explained below. Here is the content of HelloWorld.java file: package com.tutorialspoint; public class HelloWorld { private String message; public void setMessage(String message){ this.message = message; } public void getMessage(){ System.out.println("Your Message : " + message); } public void init(){ System.out.println("Bean is going through init."); } public void destroy(){ System.out.println("Bean will destroy now."); } } Following is the content of the MainApp.java file. Here you need to register a shutdown hookregisterShutdownHook() method that is declared on the AbstractApplicationContext class. This will ensures a graceful shutdown and calls the relevant destroy methods. package com.tutorialspoint; import org.springframework.context.support.AbstractApplicationContext; import org.springframework.context.support.ClassPathXmlApplicationContext;
- 15. public class MainApp { public static void main(String[] args) { AbstractApplicationContext context = new ClassPathXmlApplicationContext("Beans.xml"); HelloWorld obj = (HelloWorld) context.getBean("helloWorld"); obj.getMessage(); context.registerShutdownHook(); } } Following is the configuration file Beans.xml required for init and destroy methods: <?xml version="1.0" encoding="UTF-8"?> <beans xmlns="http://www.springframework.org/schema/beans" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:schemaLocation="http://www.springframework.org/schema/beans http://www.springframework.org/schema/beans/spring-beans-3.0.xsd"> <bean id="helloWorld" class="com.tutorialspoint.HelloWorld" init-method="init" destroy-method="destroy"> <property name="message" value="Hello World!"/> </bean> </beans> Once you are done with creating source and bean configuration files, let us run the application. If everything is fine with your application, this will print the following message: Bean is going through init. Your Message : Hello World! Bean will destroy now. Default initialization and destroy methods: If you have too many beans having initialization and or destroy methods with the same name, you don't need to declare init-method and destroy-method on each individual bean. Instead framework provides the flexibility to configure such situation using default-init-method and default-destroy-methodattributes on the <beans> element as follows: <beans xmlns="http://www.springframework.org/schema/beans" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:schemaLocation="http://www.springframework.org/schema/beans http://www.springframework.org/schema/beans/spring-beans-3.0.xsd" default-init-method="init" default-destroy-method="destroy"> <bean id="..." class="..."> <!-- collaborators and configuration for this bean go here --> </bean> </beans>