Error handling in XPages
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This document discusses error handling techniques in various programming languages and frameworks including @Formulas, JavaScript, Java, Lotusscript, and XPages. It provides examples of try/catch blocks to handle exceptions, throwing custom errors, and registering general error handlers. The key approaches discussed are anticipating errors, using defensive programming, throwing and catching custom exceptions, and handling errors at different levels to provide user-friendly messages.
![Standard try - catch routine
try {
// call a function that could error out
var result = getInvoiceNumbers(customerNumber,invoiceDate);;
}
catch (e) {
result = "Error in retrieving invoices";
}
// optional use finally runs after the try/catch block
finally {
window.Forms[0].fldname.value = result
}
Throw your own errors
if (number > 10) { throw "NumberTooHighError" }](https://image.slidesharecdn.com/errorhandlinginxpagesjsjavals-110106083831-phpapp02/85/Error-handling-in-XPages-8-320.jpg)
![class CustomException extends Exception {
public CustomException(String msg){
super(msg);
}
}
public class Test {
public static void main(String[] args) {
try {
System.out.println(divide(4,0));
}
catch (CustomException e) { e.printStackTrace(); }
}
static int divide(int first,int second) throws CustomException{
if(second==0) throw new MyException("dividing by zero");
return first/second;
}
}](https://image.slidesharecdn.com/errorhandlinginxpagesjsjavals-110106083831-phpapp02/85/Error-handling-in-XPages-16-320.jpg)
Error handling in XPages
- 1. errorhandling techniques in XPages, Javascript, Java, Lotusscript and @Formulas
- 2. What is error handling? Errorhandling in: ◦@Formula ◦Javascript ◦Lotusscript ◦Java ◦xPages Openlog
- 3. Anticipate, detect and process of programming, user and environment failures or errors Prevent partially by defensive programming What counts is what you do with the errors
- 6. • Loads of cryptical error messages – no info about triggered events • No central error handling possible - be sparse with your @Formulas - use display fields for re-usable calculations • Defensive programming (@IsError, Test DataTypes: @Elements, @IsTime, @IsNumber, @Text ...)
- 8. Standard try - catch routine try { // call a function that could error out var result = getInvoiceNumbers(customerNumber,invoiceDate);; } catch (e) { result = "Error in retrieving invoices"; } // optional use finally runs after the try/catch block finally { window.Forms[0].fldname.value = result } Throw your own errors if (number > 10) { throw "NumberTooHighError" }
- 9. Try - catch routine based on error type try { var result = getInvoiceNumbers(customerNumber,invoiceDate); } catch (e if e == "CustomerNumberException") { result = "Incorrect customerNumber"; } else if e == "DateErrorException") { result = "Incorrect Date"; } else result = "Error in retrieving invoices"; }
- 10. To register a general errorHandler use: (window.)onerror=functionname() This function will have 3 input variables like: function functionname(msg,url,line_num) You can use these variables to log/show the error details
- 12. ◦ use On Error blocks ◦ is a big nono .. you are supposed to On Error resume next handle things, not ignoring them ◦ You have differtent audiences: users, developers, administrators. So throw custom errors. ◦ Then handle specific errors ◦ Option Declare prevents some programmatic errors ◦ Create a template in the new 8.5.1 LS IDE for your error new! handling blocks in subs and functions
- 14. • As with JavaScript use try - catch - finally blocks and throw/catch custom errors Try { List list = new ArrayList(getInvoiceNumbers(customerNumber,invoiceD ate)); } catch ( IOException e) { // handle/log this error } catch ( OtherErrorException e) { // again handle this } catch (Exception e) { // other errors } // optional }finally { }
- 15. • Chose: o Handle errors in subfunctions o Throw the error back to higher functions private Integer convertToInteger(String str) { try { Integer intObj2 = Integer.valueOf(str) } catch (e) { // do something } return int; } private Integer convertToInteger(String str) throws NumberFormatException { Integer intObj2 = Integer.valueOf(str) }
- 16. class CustomException extends Exception { public CustomException(String msg){ super(msg); } } public class Test { public static void main(String[] args) { try { System.out.println(divide(4,0)); } catch (CustomException e) { e.printStackTrace(); } } static int divide(int first,int second) throws CustomException{ if(second==0) throw new MyException("dividing by zero"); return first/second; } }
- 18. Error handling in xPages • Default errorpage on server (admin can change xspnsfxsp.properties) • Set errorpage in application • Custom Error page (general, debug, specific) • Logging to AgentLog
- 19. how wonderful, free stuff
- 20. • JavaScript • Java • XPages • Lotusscript DEMO!!!!!!
- 21. ◦ Getting it to work is NOT ENOUGH! ◦ Always add errorhandling to production code ◦ Thou shall avoid the use of hard coded stuff ◦ When not sure: check ◦ If it can go wrong, it will go wrong. At one point. ◦ Think first, then build your logic ◦ Do not repeat code ◦ Use only one line of code in events (click, query*) ◦ Your users are dumb ... but: you are even dumber (if you ignore them) ◦ Make your code beautiful: comment not what, but why and use meaningfull names
- 22. Vince Schuurman Martin Schaefer [email protected] [email protected]