Take a Trip Into the Forest: A Java Primer on Maps, Trees, and Collections

Take aTrip into the Forest:A Java Primer on
Maps,Trees, and Collections
Sep. 8, 2016

This webinar is brought to you as part of the
free monthly webinar series from:

Howard Greenberg
@TLCC
Paul Della-Nebbia
@PaulDN
Courtney Carter
@Teamstudio

Teamstudio provides products that help
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5
Take a Trip Into the Forest - A Java Primer on
Maps, Trees, and Collections

Your Presenter Today – Howard Greenberg
• Certified Lotus Instructor since R3
• Co-founded TLCC in 1997
• IBM Champion
• Prior to that 12 years at IBM in the PC group
• Also…
– Certified Public Accountant
– Certified Information Systems Auditor (CISA)
– Certified Flight Instructor
6

Agenda
• Why Use Java Objects in Xpages?
• Introduction to Managed Beans
• Scoped Variables in SSJS
• Introduction to Maps
• The DataObject Implementation
• A Reporting Example
• Questions???
7

Why Use Java in XPages?
• Performance (see my recorded webinar)
• Reporting
– Easily combine data from different sources
• Portability
– Back end
– Front end
• Code Maintenance
• Lots of code/knowledge out there
8

Review - Managed Beans
• The XPages runtime manages the creation of your
“managed bean”
– Request, View, Session, or Application scope
• Refer to methods on your XPages or from other Java
code
• How to:
– Create an entry in the Faces-Config file
– Create your Java code
• Getters and Setters
• No argument constructor
• Don’t have to use Managed Beans!
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SampleBean.java
SampleBeanDemo.xsp

Scoped Variables in SSJS
• sessionScope.testName
– read/write to a variable that is session scope
• Can store anything (string, Boolean, date, array, etc)
– Just don’t store Domino objects
• Why do we care???
– Scoped variables are stored as HashMaps
– Another way to access is:
• sessionScope.get(“testName”)
• sessionScope.put(“testName” , “A value”)
• Same as a Java Hash Map
– Let’s Learn more about these HashMaps!
10

Some Java Terms - Collections, Interfaces and implementations
• Collections is a Framework/root interface
– Architecture for representing collections
• Has Interfaces, Implementations, Algorithms
• Interfaces
– Abstract Data Type
– Defines a base used by all the classes that implement
• An interface in Java is similar to a class, but the body of
an interface can include only abstract methods and final fields
(constants). A class implements an interface by providing code for
each method declared by the interface.
• Implementations
– A class that uses an interface (we use this!)
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Java HashMap Documentation
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Java documentation on HashMap

Some Different Collection Implementations
• Set, SortedSet
– No duplicate elements
• HashSet, TreeSet, LinkedHashSet
• List
– Allows duplicates
– Ordered
• ArrayList, LinkedList
• Map, SortedMap
– Key/Value pairs
• HashMap, LinkedHashMap, TreeMap
15

Use Case: Configuration Data
• Goal
– Store configuration information
– Managed Bean with Application Scope
• Best choice is a HashMap
– Why? Back to the previous chart!
– Access values with a key
17

Working with Maps
• Creation
private HashMap<String,String> configData = new HashMap<String,
String>();
• Set a value
configData.put(key ,value);
• Get a value (and test to see if key is there)
public String getConfig(String key) {
String rtnString = "";
if (this.configData.containsKey(key)){
rtnString = this.configData.get(key);
}
return rtnString;
}
18

Steps
1. Notes view/form to hold configuration data
2. Create new Java Class
3. Add Managed Bean to faces-config
– Set scope as needed
4. Implement Serializable in the Java class
5. Create “private” variable for HashMap
6. Create constructor to initialize data
– Walk the view to load up the keys/values
7. Generate Getter/Setter
8. Use on XPage or in other Java code
19
ConfigBean.java
ConfigBeanDemo.xsp

More on HashMaps - Iterate through Map
• Get all the keys as a Set
– statesHashMap.keySet()
• Get all the values as a Set
– statesHashMap.values()
• Get the key and value as a Set
– statesHashMap.entrySet()
• Get the key with getKey() and the value with
getValue()
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for (Entry<String, String> state :statesHashMap.entrySet()){
myString = state.getValue() + "|" + state.getKey() ;
debugMsg(myString);
}

LinkedHashMap
• A HashMap does not keep the insertion order (random)
• Need to keeps insertion order?  LinkedHashMap
• Good when loading data from a Notes view (that is
ordered already)
– Keeps same (insertion) order
• Otherwise basically the same as HashMap
21

ArrayLists
• A list of objects (like an Array)
– Hold any data type/object
– Can search the values
– Can access an element in a certain position
• Perfect for feeding to:
– Values in a combo box, list box, etc.
– Repeats
– Data Tables
• To add at end:
– rtnList.add(stateLine);
22

Use Case: Return values to a Combo Box
• Stop doing @DbColumns
– Slow!
• Load values from a view, store in memory
– FAST!
• Use Expression Language
– configBean.statesHashMap
• Use same ConfigBean as before (application scope)
– Method in Java is getStatesHashMap()
– Returns a List
23
ConfigBean.java
ConfigBeanDemo.xsp

Time Out for a Message!
• Do you Recycle?
– View looping
– NotesDateTime?
– columnValues with a Date creates NotesDateTime objects
• Instead use the Domino API
– Simpler code patterns
– Never have to worry about recycle
– Try/Catch block not required
– Support for logging
– Lots of cool new stuff
• Available on OpenNTF – Link to version 3
– Get help via Slack/Stack Overflow
24

Code Comparison – The Old Way
25
private void initBean(Database curDb, String viewName) {
try {
View setupVw = curDb.getView(viewName);
String key = "";
String value = "";
ViewEntry tempEntry;
if (setupVw != null) {
ViewEntryCollection vwEntryCol = setupVw.getAllEntries();
ViewEntry entryDoc = vwEntryCol.getFirstEntry();
while (entryDoc != null){
Vector<?> colValues = entryDoc.getColumnValues();
key = (String) colValues.elementAt(0);
value = (String) colValues.elementAt(1);
this.configData.put(key , value);
tempEntry = vwEntryCol.getNextEntry(entryDoc);
entryDoc.recycle();
entryDoc = tempEntry;
}
}
} catch (Exception e) {
e.printStackTrace();
}
}

Code Comparison – The Domino API Way
26
private void initBean(Database curDb, String viewName) {
View setupVw = curDb.getView(viewName);
String key = "";
String value = "";
if (setupVw != null) {
for (ViewEntry entryDoc : setupVw.getAllEntries()){
Vector<?> colValues = entryDoc.getColumnValues();
key = (String) colValues.elementAt(0);
value = (String) colValues.elementAt(1);
this.configData.put(key , value);
}
}
}
No Recycle!
Uses a for loop
No Try/Catch block
ConfigBean2.java
DomAPIDemo.xsp

Ordered Lists
• Use Case
– Get a list of values always sorted by the value
• “Natural” sort order
– No duplicates
• TreeSet!
• Good for looping through a view, getting a value
from a column
– Add to TreeSet and then you always have a
sorted, unique list
27
TreeSetBean.java
TreeSetBeanDemo.xsp

Custom Sorting of a TreeSet
• Suppose you don’t want the “natural” order???
– Use a custom sort when defining the TreeSet
– Comparator function
– Will always sort using this new sort definition
28
public List<String> getArizonaTownsReversed() {
TreeSet<String> sorted = new TreeSet<String>(new Comparator<String>() {
public int compare(String o1, String o2) {
return o2.compareTo(o1);
}
});
sorted.addAll(ArizonaTowns);
return new ArrayList<String>(sorted);
}
TreeSetBean.java
TreeSetBeanDemo.xsp

Add all the towns in all the states in one object?
• Use a TreeMap
– Key,Value pair
• In this case, a state is the key, a list of towns
(TreeSet) is the value
– Sorted on the Key value, natural order
29

DataObject
• Way to implement an interface that works well
with the Expression Language
– Any data type
– Must implement certain methods
30
DataObjectBean.java
DataObjectBeanDemo.xsp

Filtering and Sorting
• Goal is to store information in the bean to allow fast
filtering and sorting
• Base storage is a LinkedHashMap
– Key is the city name
– Values are an ArrayList
• The ArrayList holds a Person object
–First and last name, city, state, email, etc.
–Universal doc id to retrieve Notes document
31

Data Model
32
Houston
LinkedHashMap<String,ArrayList
<Person>> customers
Key is City Name
Lorie Mason
Brad Hunt
Jessie Lang
Mark Travis
firstName
lastName
City
State
eMail
Notes ID
DocUNID
Person ObjectDallas
Austin
ArrayList<Person>
The customers HashMap
stores all the people from a
selected state

More on Filtering and Sorting
• Methods of the Bean are used to:
– Return data as an ArrayList to a Repeat
• Sorted (last name, city, email)
• Filter on a city or show all
– Switch to a different state
– Get the cities for the selected state (unique, ordered)
– Store information like:
• City filter
• Desired sorting
• Ascending or Descending sorting
33
ReportBean.java
ReportBeanDemo.xsp

Homework and Resources
• TLCC’s Java Classes (two)
http://www.tlcc.com/admin/tlccsite.nsf/coursedetails.xsp?ccode=ND9XJVKPG
• My Session on Xpages Performance (recorded)
– October, 2015
http://www.tlcc.com/admin/tlccsite.nsf/pages/recorded-xpages-
webinars?opendocument
• List of Collections with a summary of features
– http://www.janeve.me/articles/which-java-collection-to-use
• The Sun Java documentation (version 6, aka 1.6)
• StackOverflow
• Google!!!
34

35
 Email: howardg@tlcc.com
 Twitter: @TLCCLtd
 Web: www.tlcc.com
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Then ask your questions in the
Questions panel!
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questions verbally

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@PaulDN
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Howard Greenberg
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Paul Della-Nebbia
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