A catch about exceptions
Hi,
While I was working on analyses that constructed intermediate representations from bytecodes, I got stumped by 2 structures that I found in the bytecode.
1> An exit monitor is alwasy guarded by an exception entry. If this exception nesting is followed, one will arrive at this
60: astore 6
62: aload_3
63: monitorexit
Exception table:
60 64 60 any
Clearly this is a recursive block. This also means if one succeeds to dabble [63] to raise an exception. Then, it leads to insecure code which can loop forever without any failure. Am I right? Or have I missed anything from the JVM spec that suggests otherwise?
2> Consider the following exception table.
Exception table:
from to target type
25 28 31 any
31 36 31 any <--
20 30 39 any
31 43 39 any <--
The first arrow (<---) marked line is the safe catch for the nested monitorexit instruction and the second is from the enclosing monitorexit statement. If the exceptions caught by both handlers are java.lang.Throwable, then I guess 31-36 would be handled at 31 and 36-43 would be handled by 39. If so, why does both jikes and javac compile such exception table? Am I missing something here?
catch (CrosspostException cpe)
http://forum.java.sun.com/thread.jsp?thread=440380&forum=37&message=1983409
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Is it possible to get details about Exception catched in Exception branch of the Block in Integration Process (BPM)?
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Not able to catch the exception
Hi,
I'm trying to run an ADF page (Test.jspx) . The only page content I have is an embedded BI report.
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You are using a version of JDeveloper that isn't available to the general public, and are asking about it on a public forum. You should use the internal Oracle forum - I don't know the URL, because I am one of the unwashed general public ;)
John -
Why do I need to catch this exception?
Hello all
This is a question about exception handling. I have to build a diary application that lets you save reminders on particular dates using xml. Just to make it a little tougher, I was not allowed to use the Calendar class. This is the code I wrote:
import java.awt.*;
import java.awt.event.*;
import javax.swing.*;
import java.util.*;
import java.text.*;
import javax.xml.parsers.*;
import org.xml.sax.*;
import java.io.*;
import org.w3c.dom.*;
import javax.xml.transform.*;
import javax.xml.transform.dom.*;
import javax.xml.transform.stream.*;
import static java.lang.Math.*;
public class CalendarAssignment extends JFrame implements ActionListener
int MonthLength [] = { 31, 28, 31, 30, 31, 30, 31, 31, 30, 31, 30, 31 };
public JButton [] days = new JButton[43];
private JLabel lbl, reminderlbl;
private JPanel top, grid, remindercenter, reminderbottom;
private JFrame reminderframe;
private JTextField year1, reminderinput, dayno;
private JComboBox months;
private Container container;
private JButton fetch, save, cancel;
private Document doc;
private File file;
private Node node;
private String year, month, day;
public static void main( String[] args ) {
CalendarAssignment c = new CalendarAssignment( );
c.setSize( 400, 300 );
c.setDefaultCloseOperation( JFrame.EXIT_ON_CLOSE );
c.show( );
public CalendarAssignment( ) {
int CurrentYear, CurrentMonth;
String YearString, MonthString, Now;
Date today;
container = getContentPane( );
container.setLayout( new BorderLayout( ) );
SimpleDateFormat DateFormatter;
DateFormatter = new SimpleDateFormat( "MM.yyyy" );
today = new Date( );
Now = DateFormatter.format( today );
MonthString = Now.substring( 0,2 );
YearString = Now.substring( 3,7 );
CurrentMonth = Integer.valueOf( MonthString );
CurrentYear = Integer.valueOf( YearString );
top = new JPanel( );
String [] items = { "January", "February", "March", "April", "May", "June",
"July", "August", "September", "October", "November",
"December" };
months = new JComboBox( items );
months.setEditable( false );
months.setSelectedIndex( CurrentMonth - 1 );
year1 = new JTextField( );
year1.setText( YearString );
year1.setEditable( true );
year1.setHorizontalAlignment( year1.CENTER );
fetch = new JButton( "Fetch Month" );
fetch.addActionListener( this );
top.setLayout( new GridLayout( 1, 3, 20, 0 ) );
top.add( months );
top.add( year1 );
top.add( fetch );
grid = new JPanel( );
grid.setLayout( new GridLayout( 7, 7, 0, 0 ) );
String [] week = { "Mon", "Tue", "Wed", "Thur", "Fri", "Sat", "Sun" };
for ( int a = 0; a < 7; a ++ ) {
JLabel lbl = new JLabel( week[a], JLabel.CENTER );
grid.add( lbl );
for ( int i = 0; i < 42; i ++ ) {
days[i] = new JButton( );
grid.add( days[i] );
days.addActionListener( this );
DrawCalendar( CurrentMonth, CurrentYear );
container.add( top, BorderLayout.NORTH );
container.add( grid, BorderLayout.CENTER );
private void DrawCalendar( int SelectMonth, int SelectYear ) {
int DisplayMonthLength, Buttons;
String ButtonID = "";
int OffSet = MonthStart( SelectMonth, SelectYear );
DisplayMonthLength = MonthLength [SelectMonth - 1];
if ( SelectMonth == 2 )
DisplayMonthLength += LeapYear( SelectYear );
for ( Buttons = 1; Buttons < 43; Buttons ++ ) {
if ( ( Buttons <= OffSet ) || ( Buttons > ( DisplayMonthLength + OffSet ) ) ) {
ButtonID = "";
days[Buttons-1].setEnabled( false );
else {
ButtonID = Integer.toString( Buttons - OffSet );
days[Buttons-1].setEnabled( true );
days[Buttons-1].setLabel( ButtonID );
grid.add( days[Buttons-1] );
private int LeapYear( int year ) {
int FourHundred, OneHundred, Fourth;
FourHundred = year % 400;
OneHundred = year % 100;
Fourth = year % 4;
if( ( ( FourHundred == 0 ) ) || ( ( OneHundred != 0 ) && ( Fourth == 0 ) ) )
return ( 1 );
else
return ( 0 );
private int MonthStart( int Month, int Year ) {
int OffSet, LastMonths, BeforeOrAfter, Years;
int AllDays = 0;
int YearDays = 365;
int YearMonths = 12;
BeforeOrAfter = Year - 2006;
Years = abs( BeforeOrAfter );
if( BeforeOrAfter != 0 )
BeforeOrAfter = BeforeOrAfter / Years;
switch( BeforeOrAfter ) {
case 1:
for( int a = 2006; a < Year; a ++ ) {
AllDays += YearDays + LeapYear( a );
AllDays += LastMonthsCalc( Month, Year );
break;
case -1:
for( int a = 2005; a > Year; a -- ) {
AllDays += YearDays + LeapYear( a );
for( LastMonths = YearMonths; LastMonths >= Month; LastMonths -- ) {
AllDays += MonthLength[LastMonths - 1];
if( LastMonths == 2 )
AllDays += LeapYear( Year );
break;
default:
if( Month > 1 )
AllDays += ( LastMonthsCalc( Month, Year ) );
OffSet = AllDays % 7;
if( BeforeOrAfter ==( -1 ) )
return( 6 - OffSet );
else if( OffSet > 0 )
return( OffSet - 1 );
else
return( 6 );
private int LastMonthsCalc( int Month, int Year ) {
int Counter;
int days = 0;
for( Counter = 1; Counter < Month; Counter ++ ) {
days += MonthLength[Counter - 1];
if( Counter == 2 )
days += LeapYear( Year );
return( days );
public void CreateReminder( String buttonID, String yearID, String monthID ) {
reminderframe = new JFrame( );
reminderlbl = new JLabel( );
reminderframe.setLayout( new GridLayout( 2, 1, 0, 0 ) );
remindercenter = new JPanel( );
reminderlbl = new JLabel( "Please type in reminder to be saved for " + buttonID + " " + monthID + " " + yearID + ":", JLabel.CENTER );
reminderinput = new JTextField( 30 );
reminderinput.setHorizontalAlignment( reminderinput.CENTER );
reminderinput.setEditable( true );
remindercenter.setLayout( new GridLayout( 2, 1, 0, 0 ) );
remindercenter.add( reminderlbl );
remindercenter.add( reminderinput );
reminderbottom = new JPanel( );
save = new JButton( "Save" );
save.addActionListener( this );
cancel = new JButton( "Cancel" );
cancel.addActionListener( this );
dayno = new JTextField( buttonID );
dayno.setEditable( false );
dayno.setEnabled( false );
dayno.show( false );
reminderbottom.setLayout( new FlowLayout( ) );
reminderbottom.add( save );
reminderbottom.add( cancel );
reminderbottom.add( dayno );
reminderframe.setSize( 500, 75 );
reminderframe.add( remindercenter );
reminderframe.add( reminderbottom );
reminderframe.pack( );
reminderframe.show( );
public void SaveReminder( String dayID, String yearID, String monthID ) throws Exception {
file = new File( "Diary.xml" );
doc = DocumentBuilderFactory.newInstance( ).newDocumentBuilder( ).parse( file.toURL( ).toString( ) );
String year = yearID;
String month = monthID;
String day = dayID;
//System.out.println( year );
//System.out.println( month );
//System.out.println( day );
CreateEntry( doc.getDocumentElement( ) );
writeXmlFile( );
public boolean CreateEntry( Node node ) {
Node searchNode;
searchNode = getYear( node );
if( searchNode == null ) {
Element newNode = doc.createElement( "Year" );
searchNode = node.appendChild( newNode );
newNode.setAttribute( "Id", year );
node = searchNode;
searchNode = getMonth( node );
if( searchNode == null ) {
Element newNode = doc.createElement( "Month" );
searchNode = node.appendChild( newNode );
newNode.setAttribute( "Id", month );
node = searchNode;
searchNode = getDay( node );
if( searchNode == null ) {
Element newNode = doc.createElement( "Day" );
searchNode = node.appendChild( newNode );
newNode.setAttribute( "Id", day );
node = searchNode;
String entry = reminderinput.getText( );
Node textNode = doc.createTextNode( entry );
node.appendChild( textNode );
return true;
private Node getYear( Node node ) {
node = node.getFirstChild( );
while( node != null ) {
if(node.getNodeName( ).equals( "Year" ) && String.valueOf( node.getAttributes( ).item( 0 ).getNodeValue( ) ) == year )
return node;
node = node.getNextSibling( );
return null;
private Node getMonth( Node node ) {
node = node.getFirstChild( );
while( node != null ) {
if( node.getNodeName( ).equals( "Month" ) && String.valueOf( node.getAttributes( ).item( 0 ).getNodeValue( ) ) == month )
return node;
node = node.getNextSibling( );
return null;
private Node getDay( Node node ) {
node = node.getFirstChild( );
while( node != null ) {
if( node.getNodeName( ).equals( "Day" ) && String.valueOf( node.getAttributes( ).item( 0 ).getNodeValue( ) ) == day )
return node;
node = node.getNextSibling( );
return null;
private void writeXmlFile( ) throws Exception {
Source source = new DOMSource( doc );
Result result = new StreamResult( file );
Transformer xformer = TransformerFactory.newInstance( ).newTransformer( );
xformer.setOutputProperty( OutputKeys.INDENT,"yes" );
xformer.setOutputProperty( OutputKeys.DOCTYPE_SYSTEM,"Diary.dtd" );
xformer.transform( source, result );
public void actionPerformed( ActionEvent e ) {
String IDButton = e.getActionCommand( );
String IDYear = year1.getText( );
Object IDMonthObj = months.getSelectedItem( );
if( e.getSource( ) == fetch ) {
String YearText = year1.getText( );
int YearNumber = Integer.valueOf( YearText );
int MonthsIndex = months.getSelectedIndex( ) + 1;
DrawCalendar( MonthsIndex, YearNumber );
else if( e.getSource( ) == cancel ) {
reminderframe.hide( );
else if( e.getSource( ) == save ) {
String IDDay = dayno.getText( );
String IDMonth = String.valueOf( IDMonthObj );
SaveReminder( IDDay, IDYear, IDMonth );
else {
String IDMonth = String.valueOf( IDMonthObj );
Toolkit.getDefaultToolkit( ).beep( );
int n = JOptionPane.showConfirmDialog( null, "Set reminder on this date?", "Question", JOptionPane.YES_NO_OPTION );
if( n == JOptionPane.YES_OPTION ) {
CreateReminder( IDButton, IDYear, IDMonth );
If you compile it, you will realise that I get an error about exception handling. My lecturer gave me an example code of how to do the same thing without using a GUI:
import javax.xml.parsers.*;
import org.xml.sax.*;
import java.io.*;
import java.util.*;
import org.w3c.dom.*;
import javax.xml.transform.*;
import javax.xml.transform.dom.*;
import javax.xml.transform.stream.*;
public class CallDOM
Document doc;
File file;
Scanner input;
int year, month, day;
String currentYear, currentMonth;
public static void main(String args[]) throws Exception
CallDOM cd=new CallDOM();
CallDOM() throws Exception
file=new File("Diary.xml");
//create DOM from file
doc = DocumentBuilderFactory.newInstance().newDocumentBuilder().parse(file.toURL().toString());
input=new Scanner(System.in);
System.out.println("1) Create entry");
System.out.println("2) Read entry");
System.out.println("3) Show Diary");
System.out.println("4) Quit");
int choice=input.nextInt();
while(choice!=4)
switch(choice)
case 1: GetDate();CreateEntry(doc.getDocumentElement());break;
case 2: GetDate();ReadEntry(doc.getDocumentElement());break;
case 3: ShowDiary(doc.getDocumentElement());
System.out.println("1) Create entry");
System.out.println("2) Read entry");
System.out.println("3) Show Diary");
System.out.println("4) Quit");
choice=input.nextInt();
writeXmlFile();
public void GetDate()
System.out.println("Enter date (dd mm yyyy)");
day=input.nextInt();
month=input.nextInt();
year=input.nextInt();
public boolean ReadEntry(Node node)
node = getYear(node);
if(node==null) return false;
node = getMonth(node);
if(node==null) return false;
node = getDay(node);
if(node==null) return false;
node = node.getFirstChild();
while(node!=null)
System.out.println(node.getNodeValue().trim());
node=node.getNextSibling();
return true;
public boolean CreateEntry(Node node)
Node searchNode;
searchNode = getYear(node);
if(searchNode==null)
Element newNode = doc.createElement("Year");
searchNode = node.appendChild(newNode);
newNode.setAttribute("Id",Integer.toString(year));
node = searchNode;
searchNode = getMonth(node);
if(searchNode==null)
Element newNode = doc.createElement("Month");
searchNode = node.appendChild(newNode);
newNode.setAttribute("Id",Integer.toString(month));
node = searchNode;
searchNode = getDay(node);
if(searchNode==null)
Element newNode = doc.createElement("Day");
searchNode = node.appendChild(newNode);
newNode.setAttribute("Id",Integer.toString(day));
node = searchNode;
System.out.println("Enter Text");
String entry=input.next();
entry+=input.nextLine();
Node textNode = doc.createTextNode(entry);
node.appendChild(textNode);
return true;
public void ShowDiary(Node node)
Stack<Node> stack=new Stack<Node>();
Node child;
stack.push(node);
while(!stack.empty())
node = stack.pop();
if(ProcessNode(node))
child = node.getLastChild();
while(child!=null)
stack.push(child);
child = child.getPreviousSibling();
private boolean ProcessNode(Node node)
if(node.getNodeName().equals("Year"))
currentYear=node.getAttributes().item(0).getNodeValue();
if(node.getNodeName().equals("Month"))
currentMonth=node.getAttributes().item(0).getNodeValue();
if(node.getNodeName().equals("Day"))
System.out.print(node.getAttributes().item(0).getNodeValue()+"/"+
currentMonth+"/"+currentYear+": ");
node=node.getFirstChild();
while(node!=null)
System.out.println(node.getNodeValue().trim());
node=node.getNextSibling();
return false;
return true;
private Node getYear(Node node)
node=node.getFirstChild();
while(node!=null)
if(node.getNodeName().equals("Year")
&& Integer.valueOf(node.getAttributes().item(0).getNodeValue())==year)
return node;
node = node.getNextSibling();
return null;
private Node getMonth(Node node)
node=node.getFirstChild();
while(node!=null)
if(node.getNodeName().equals("Month")
&& Integer.valueOf(node.getAttributes().item(0).getNodeValue())==month)
return node;
node = node.getNextSibling();
return null;
private Node getDay(Node node)
node=node.getFirstChild();
while(node!=null)
if(node.getNodeName().equals("Day")
&& Integer.valueOf(node.getAttributes().item(0).getNodeValue())==day)
return node;
node = node.getNextSibling();
return null;
private void writeXmlFile() throws Exception
Source source = new DOMSource(doc);
Result result = new StreamResult(file);
Transformer xformer = TransformerFactory.newInstance().newTransformer();
xformer.setOutputProperty(OutputKeys.INDENT,"yes");
xformer.setOutputProperty(OutputKeys.DOCTYPE_SYSTEM,"Diary.dtd");
xformer.transform(source, result);
}My question is, why does the exceptions in the example code not need to be caught? And why do I have to catch the exceptions in my code? Several exceptions are thrown in the example code, but there is no catch statement.
Thanks for any advice!!Since your question didn't come with any relevant details, and since you have huge steaming piles of irrelevant code, all I can give is a general answer to "Why do I need to catch this exception?"
[url http://java.sun.com/docs/books/tutorial/essential/exceptions/index.html]Exception tutorial at http://java.sun.com/docs/books/tutorial/essential/exceptions/index.html
Here's a quick overview of exceptions:
The base class for all exceptions is Throwable. Java provides Exception and Error that extend Throwable. RuntimeException (and many others) extend Exception.
RuntimeException and its descendants, and Error and its descendants, are called unchecked exceptions. Everything else is a checked exception.
If your method, or any method it calls, can throw a checked exception, then your method must either catch that exception, or declare that your method throws that exception. This way, when I call your method, I know at compile time what can possibly go wrong and I can decide whether to handle it or just bubble it up to my caller. Catching a given exception also catches all that exception's descendants. Declaring that you throw a given exception means that you might throw that exception or any of its descendants.
Unchecked exceptions (RuntimeException, Error, and their descendants) are not subject to those restrictions. Any method can throw any unchecked exception at any time without declaring it. This is because unchecked exceptions are either the sign of a coding error (RuntimeException), which is totally preventable and should be fixed rather than handled by the code that encounters it, or a problem in the VM, which in general can not be predicted or handled. -
Catching an exception (help)!!!
Hi everyone, the problem i have is when the user enters a number that is out of bounds (higher or lower than the excepted values it should prompt the program to write to the screen "out of range, try again" or something along those lines.
However, it instead just prints "error - program terminated" which is the message that should be printed when there is a different problem within the program.
Can anyone help me get the program to print the correct messages, you can see what i mean from the code:
import java.io.*;
import java.util.ArrayList;
public class FlatCost {
ArrayList floors = new ArrayList();
public FlatCost(String filename) {
try {
readDataFromFile(filename);
BufferedReader in = new BufferedReader(new InputStreamReader(System.in));
int floor;
int rooms;
String another = "y";
while(another.equalsIgnoreCase("y")) {
System.out.print("\nEnter floor number (0 for ground): ");
floor = Integer.parseInt(in.readLine());
if(floor < 0 || floor > floors.size()) {
System.out.println("floor out of range, try again");
else {
System.out.print("\nEnter no. rooms: ");
rooms = Integer.parseInt(in.readLine());
if(rooms < 0 || rooms > ((String[])floors.get(floor)).length) {
System.out.println("rooms out of range, try again");
else {
System.out.println("\nThe cost of a "+rooms+"-room flat on floor "+floor+" is "+
((String[])floors.get(floor))[rooms+1]+" per month");
System.out.print("\nAnother? (y/n): ");
another = in.readLine();
catch(Exception e){
System.out.println("error - program terminated");
public void readDataFromFile(String filename)throws Exception {
BufferedReader br = new BufferedReader(new FileReader(filename));
String line = "";
while((line = br.readLine()) != null)
floors.add(line.split(" "));
br.close();
public static void main(String args[])throws IOException{
new FlatCost(args[0]);
}any help is appreciated
thanks
Sarah xI barely know where to begin.
Start by printing out the stack trace when you catch an exception. That'll give you more information than the message you're printing out. You know the program is terminating - you need to know why.
You're writing in a VERY procedural style. There's little or nothing object-oriented about what you're doing.
You've got a bunch of stuff in that constructor that really doesn't belong there. You shouldn't have code to continuously ask a client for a floor and room number in a constructor. That really belongs in an application that drives the object, like the main method that you wrote.
Your FlatCost can read in a file that contains floor/room/price information, but if I were writing the application I'd read it in and store it in the ArrayList as you've done. Then I'd have a getCost() method that would take floor and room count as parameters and return the total cost.
Learning how to program is learning how to debug. I'd rewrite things a little bit and put System.out.println() statements into the code to narrow down exactly where the error was occurring and why. It won't take you long to figure it out. You don't even need a fancy debugger or IDE. -
Catching an exception thrown from another thread
I have a SocketServer that creates new threads to handle incoming clients. If one of the threads throw a SQLException is it possible to catch that exception in the SocketServer that created that thread.
I tried implementing this code and I cannot get the server to catch an exception thrown in the thread. Are my assumptions correct?
I was reading something about Thread Groups and implementing an uncoughtException() method, but this looked like overkill.
Thanks for your time!
Some Example code would be the following where the ClientThread will do a database query which could cause an SQLException. I'd like to catch that exception in my Socket Server
try
new ClientThread( socketServer.accept() , host, connection ).start();
catch( SQLException e )
System.out.println( "DataSource Connection Problem" );
e.printStackTrace();
}hehe, why?
The server's job is to listen for an incoming message from a client and pass it off to a thread to handle the client. Otherwise the server will have to block on that incoming port untill it has finished handling the client and usually there are many incoming clients continuously.
The reason I would want to catch an exception in the server based on the SQLException thrown in the thread is because the SQLException is usually going to be due to the fact the datasource connection has become unavalable, or needs to be refreshed. This datasource connection is a private variable stored in the socket server. The SocketServer now needs to know that it has to refresh that datasource connection. I would normally try to use somesort of flag to set the variable but to throw another wrench into my dilemma, the SocketServer is actually its own thread. So I can't make any of these variables static, which means I can't have the thread call a method on teh socket server to change the status flag. :)
I guess I need implement some sort of Listener that the thread can notify when a datasource connection goes down?
Thanks for the help so far, I figured java would not want one thread to catch another thread's exceptions, but I just wanted to make sure. -
Write and read txt files and catch the exceptions
hey everyone, im in a bit of a bind. im trying to set up this try catch statement. here is what i have for code so far.
import java.util.Scanner;
import java.io.*;
public class Warning
// Reads student data (name, semester hours, quality points) from a
// text file, computes the GPA, then writes data to another file
// if the student is placed on academic warning.
public static void main (String[] args)
int creditHrs; // number of semester hours earned
double qualityPts; // number of quality points earned
double gpa; // grade point (quality point) average
String line, name, inputName = "students.dat";
String outputName = "warning.dat";
try
Scanner FileScan1 = new Scanner (new File("students.dat"));
// Set up scanner to input file
// Set up the output file stream
// Print a header to the output file
outFile.println ();
outFile.println ("Students on Academic Warning");
outFile.println ();
// Process the input file, one token at a time
while (FileScan1.hasNext())//there is another line...
{ // Get the credit hours and quality points and
// determine if the student is on warning. If so,
// write the student data to the output file.
// Close output file
catch (FileNotFoundException exception)
System.out.println ("The file " + inputName + " was not found.");
catch (IOException exception)
System.out.println (exception);
catch (NumberFormatException e)
System.out.println ("Format error in input file: " + e);
}I am pretty sure the layout is good to go, but first and foremost that try statement is hanging me up. Could someone give me some suggestions about how i should set this up.
i want to read in this students.dat file, then output another file called warning.dat.
Thanks i really appreicate the help.no, i was really hoping to just see if the way it is
set up it will be doable, that way i wouldn't be
working on code that was impossiable to sort through
properlyFair enough.
One thing I'd suggest is that if you're really basically only going to be printing the exceptions, and since that is the top-level method (main) --
I'd instead just add some "throws" clauses to main, get rid of the try/catch stuff, and just let the VM handle the exceptions for you. It will print them, just like you're doing, except that it will also print the stack traces, which you are not doing.
If you're going to handle exceptions, it's better to actually do something about them rather than just print them - otherwise you might just as well let the runtime do that for you. -
Hello,
Why it did not throw an exception?
void mymethod() throws Exception()
int x = 1;
if (x == 0)
throw new Exception();
try{
x = 0;
catch(Exception e)
System.out.println(e);
}Why it did not throw an exception?Why did you think it should ?
void mymethod() throws Exception()
int x = 1;
// x is NOT equal to zero
if (x == 0)
// SO this is not executed
throw new Exception();
try{
// x is assigned to zero
x = 0;
// But there is no reason to throw an exception
} catch(Exception e) {
// So this code is never executed.
System.out.println(e);
}You have misunderstood something (possibly two or three things) about exceptions. -
Centralized way of catching unexpected Exceptions in Java?
Hi Guys,
Is there a centralized way to catch unexpected Exceptions in Java?
Here's an example:
public static void main(String[] args)
try
new Thread()
public void run()
String s = null;
//NullPointerException is thrown here
s.indexOf(12);
}.start();
catch (Exception ex)
System.err.println("This is not called");
ex.printStackTrace();
}Think about a program error, that the program is not prepared for, i.e. NullPointerException or an ArrayIndexOutOfBounds exception.
What I'm after is not like "put critical block in try-catch", but something like registering a global ExceptionListener in java.lang.Runtime, a monitoring MBean or something that I could use in my program to do a simple exception logging.
Any idea, help would be greatly appreciated!
peterNullPointerException , IOException ....all are subclasses of the base class Exception, so catch(Exception) will catch any exception in the current thread. So modify ur code a bit
public static void main(String[] args)
new Thread()
public void run()
try{
String s = null;
//NullPointerException is thrown here
s.indexOf(12);
catch (Exception ex)
System.err.println("This is not called");
ex.printStackTrace();
}.start();
..... -
A catch-all "exception handler" - what's the end of an stack trace?
I've created an application that is beeing tested these days, and I thought it would be a good idea to implement a "catch-all" exception handler so that I could notify the user when an exception occur (so that he may stop, send me the log, and to prevent errors that occur as a result of the first one).
The way I've started implementing it is I redirect error out to a custom output stream:
public class ConsoleOutStream extends ByteArrayOutputStream {
private JFrame owner;
public ConsoleOutStream(JFrame owner) {
this.owner = owner;
* Writes <code>len</code> bytes from the specified byte array
* starting at offset <code>off</code> to this byte array output stream.
* @param b the data.
* @param off the start offset in the data.
* @param len the number of bytes to write.
public synchronized void write(byte b[], int off, int len) {
super.write(b, off, len);
checkForExceptions();
* Writes the specified byte to this byte array output stream.
* @param b the byte to be written.
public synchronized void write(int b) {
super.write(b);
checkForExceptions();
private void checkForExceptions() {
reset();
if(this.toString().indexOf("xception") != -1) {
System.out.println("Exception!!\n\n");
System.out.println(this.toString());
}then i redirect System.err:
PrintStream out = new PrintStream(new ConsoleOutStream(this));
System.setErr(out);
The problem is that the checkForExceptions() method will be called, e.g. 3 times for each exception - and I just want to display an error message to the user once (of course).
Anyone done something similar?I'm interested in catching all "unhandled errors"how about:
public static void main(String[] args){
try{
//whatever you would normally call from main
}catch (Throwable e){
System.out.println("There was an unhandled exception:");
e.printStackTrace();
} -
Is it good practice to catch High level Exception in the try block, this would also catch RuntimeException. My personal opinion is not to catch the Runtime Exception and let the JVM handle it. However if there is a need to catch specific Runtime Exception, code should be written for that.
try
// Your code
catch (Exception e)
e.printStackTrace()
}I agree that runtime exceptions should generally not
be caught as they are mistakes of programmers.
But in order to debug a large project with hundreds of
classes it can be useful to do that anyways.
Any my big question is: how?
I tried to wrap the content of the main method in a
try / catch block hoping that I could catch all
exceptions not handled somewhere else.
But it didn't work.
I manually threw some exceptions somewhere in my GUI
and the main method wrapper didn't get them.
But the VM did and printed the exception message.
But I didn't want the VM to catch my exceptions. I
wanted to catch them myself at the lowest possible
point in my own classes.
And I thought that was the main method.
Can anyone help me?
Thank you
Matthias Klein
P.S. please excuse my improvable english; it's not my
mother tongue.AWT uses many different threads in your program that you never find out about unless something breaks. main(String arg[]) starts as the lowest possible point but, if you construct a Frame, Image, or certain other objects from the AWT package, AWT Threads automatically start over which you have little or no control.
Overall, I don't think it's actually possible to catch the Runtime Exceptions out of these Threads. The best this you can do about them is prevent them from happening. -
Catching causal exceptions from finally{} block?
I have some code that I have not developed, yet from what I can tell throws Exceptions as in the following psuedo-code:
public void foobar() throws BarException, FooException {
try {
throw new FooException();
} finally {
throw new BarException();
}This expectedly returns BarException, not FooException. Question is since FooException was thrown, is there any way to get a reference to the original cause?This is due to the good-ol' problem of cleaning up
java.sql.Connection objects to a connection pool in
the finally block yet wanting to ensure the original
exception is propagated to the calling method,
whereas the OP should catch the exception,
maintain temporary reference, then use it as a
reference to the other Exception in the finally
if there's no better way for her to do it.There's a better way to do it. You don't need to keep a temp reference to that exception in your finally block. Finally doesn't need to know anything about the exception. public void foo() {
try {
Bar bar = sqlStuff();
catch (SQLException exc) {
// This catch block will execute if SQLException is thrown at *1*
System.err.println("I got a SQLException!");
private Bar sqlStuff() throws SQLException, MyException {
try {
// *1* do something that might throws SQLException, and maybe something else
return aBar;
catch (SomeOtherException exc) {
throw new MyException(exc);
finally {
// close ResultSet, Statement, Connection
// NO EXCEPTION re-throwing
// or return aBar here
} If a SQLException is thrown inside the try block, finally will execute, and then the method will throw that original SQL exception. If SomeOtherException is thrown, it will be caught, a new MyException will be created to wrap it, the finally block will execute, and the MyException will be thrown from the method. If everything goes well, the finally block will execute, and the method will return aBar.
All this will happen without the finally block touching or knowing about any exception that was thrown before entering it. -
Best Practice: JavaFX pattern for "Catching all Exceptions"
Hi,
what is on the current JavaFX Standard the best way to catch all Exceptions (centralized) within my JavaFX application...
I read thread outside this Oracle Forum who recommend following:
1. Thread.setDefaultUncaughtExceptionHandler(new MyExceptionHandler());
--> catch all runtime exceptions
2. http://stackoverflow.com/questions/12318861/javafx-2-catching-all-runtime-exceptions
--> Implementing some source code who wrap the current GUI thread...
3. I read something like:
"JavaFX exception handling is almost identical to that in Java, apart from the fact that checked exceptions are handled in the same way as unchecked exceptions. This is good news for most Java programmers moving to JavaFX because you are no longer obliged to catch and handle exceptions."
Sounds very good! But where/how can I do this ???
Edited by: wschele on 19.02.2013 04:58
Edited by: wschele on 19.02.2013 05:16No recommendation whats the best way to do it?
Catching each Exception in different layers is boring ! :-( -
Catching the exception thrown in a java class on a JSP front end
I have a web service created in JAVA.. The modules throw certain exceptions and i am having auto generated JSP created from the WSDL's , which i can obviously edit. i want to catch these exceptions in this JSP page.. Any clue how to do this?
Thanks.Nee333 wrote:
I have a web service created in JAVA.. The modules throw certain exceptions and i am having auto generated JSP created from the WSDL's , which i can obviously edit. i want to catch these exceptions in this JSP page.. Any clue how to do this? It is not possible to catch the Exception in a JSP. You can however put any logging or even an if statement into your JSP to display the error or control the flow based on the error. -
Catching an exception in an JSF page
Hi,
I have made the following example:
In my jsf page I have:
<a4j:commandButton id="save" action="#{settings.save}"
reRender="attributes" />
<h:outputLabel value="Save" for="save" />
<table width="100%" cellpadding="0" cellspacing="0">
<!--
<tr>
<td> If exception occurs add extra buttons here for more actions
</td>
</tr>
-->
<tr>
<td><ui:include src="/attributes.xhtml">
<ui:param name="parent" value="#{settings}" />
</ui:include></td>
</tr>
</table>
In SettingsBean.java
public void save() throws exception
try
doSomething();
catch(Exception e)
// catch the exception here and send it back to the jsf page????
I want to be able to catch the exception when it occurs in my jsf page. If the exception arrises I want to add some extra buttons.
Any ideas how to resolve this?
Thanks in advanceJSF does not work like JSP, even when using JSP with JSF, in that the execution is decoupled from the page being processed. So you cannot catch exceptions in JSF views.
Assuming I have sufficiently confused you now, let me give you some ideas as to how to handle your situation. The usual way this is handled is to register a message when an exception occurs which are then displayed by <h:messages> or <h:message> components.
However, this does not appear to be suitable for your purpose as you require specialized output when the exception occurs. So you could store a flag (or even the exception itself) in a backing bean and use the rendered property of all components to conditionally display your buttons. BUT you will need to take care that the dynamic value of the rendered property will be the same on the subsequent request or the actions for the buttons will not be queued.
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