Monday, April 8, 2013

How to get current stack trace in Java for a Thread - Debugging Tutorial

Stack trace is very useful while debugging or troubleshooting any issue in Java. Thankfully Java provides couple of ways to get current stack trace of a Thread in Java, which can be really handy in debugging. When I was new to Java programming, and didn’t know how to remote debug a Java application, I used to put debug code as patch release, which uses classpath to pick debug code for printing stack trace and shows how a particular method is get called and that some time provide vital clue on missing or incorrect argument. Now, When I have couple of Java debugging tips at my sleeve, I still think knowledge of  how to get current stack trace in Java for any Thread, or simply print stack trace from any point in code worth knowing. For those who are not very familiar with stack trace and wondering what is stack trace in Java, here is quick revision. Thread executes code in Java, they call methods, and when they call, they keep them in there stack memory. You can print that stack trace to find out, from where a particular method is get called in execution flow. This is especially useful if you are using lot of open source libraries, and don’t have control on all the code. One of the most familiar face of stack trace in Java is printing stack trace using Exception.printStackTrace(), when an Exception or Error is thrown in Java. In this Java tutorial, we will look at couple of ways to print and get current stack trace of a Thread in Java.


Stack Trace for current Thread in Java

How to get current thread stack trace in Java for exception
One of the easiest way of printing stack trace of current thread in Java is by using dumpStack()  method from java.lang.Thread class. This method prints stack trace of thread on which it get's called. You can use Thread.currentThread() method to get reference of current thread before calling this method. Another way printing stack trace is using printStackTrace() method of Throwable class. Just use new Throwable().printStackTrace() method ,and it will print complete stack trace from where a method is called, into console. Main difference between using dumpStack() and printStackTrace() is first entry in Stack, In case of dumpStack() first entry is always java.lang.Thread.dumpStack(), while in later case it's the method from where you printed stack trace. If you don't want to print stack trace and rather wants it in Java program, you can use getStackTrace() method from Thread class. This method returns an array of StackTraceElement. In following Java program we will see examples of all three approaches to get stack trace of current thread in Java.


import java.util.logging.Logger;

/**
 * Java program to demonstrate how to print and get stack trace for current
 * thread in Java. Stack trace are useful information while debugging or
 * troubleshooting any issue.
 *
 * @author Javin Paul
 */
public class StackTraceExample {
    private static final Logger logger = Logger.getLogger(StringReplace.class.getName());
    
    public static void main(String args[]) {
       
        //calling a method to print stack trace further down
        first();
    } 
   
    public static void first(){
        second();
    }

    private static void second() {
        third();
    }

    private static void third() {
       
        //If you want to print stack trace on console than use dumpStack() method
        System.err.println("Stack trace of current thread using dumpStack() method");
        Thread.currentThread().dumpStack();
       
        //This is another way to print stack trace from current method
        System.err.println("Printing stack trace using printStackTrace() method of Throwable ");
        new Throwable().printStackTrace();
       
        //If you want stack trace as StackTraceElement in program itself than
        //use getStackTrace() method of Thread class
        StackTraceElement[] stackTrace = Thread.currentThread().getStackTrace();
       
        //Once you get StackTraceElement you can also print it to console
        System.err.println("displaying Stack trace from StackTraceElement in Java");
        for(StackTraceElement st : stackTrace){
          //  System.err.println(st);
        }
       
    }
   
}
Output
Stack trace of current thread using dumpStack() method
java.lang.Exception: Stack trace
        at java.lang.Thread.dumpStack(Thread.java:1249)
        at test.StringReplace.third(StringReplace.java:38)
        at test.StringReplace.second(StringReplace.java:31)
        at test.StringReplace.first(StringReplace.java:27)
        at test.StringReplace.main(StringReplace.java:23)
Printing stack trace using printStackTrace() method of Throwable
java.lang.Throwable
        at test.StringReplace.third(StringReplace.java:42)
        at test.StringReplace.second(StringReplace.java:31)
        at test.StringReplace.first(StringReplace.java:27)
        at test.StringReplace.main(StringReplace.java:23)
displaying Stack trace from StackTraceElement in Java


That's all on How to get current stack trace in Java. By using above methods you can get stack trace from current thread or any other Thread. If you are also interested on taking thread dump, than you can use kill -3 pid in UNIX environment and ctrl+break in Windows environment. This will instruct JVM to print stack trace of all threads in console.

3 comments :

Borislav Kirilov said...

I see you are declaring logger, but not using it in the example. I say that, because I'm trying to solve the same problem - to print the stack trace - but want to print it in the logger ... The thing is that the method Thread.currentThread().getStackTrace() is available since Java 1.5, but I'm using Java 1.4. Any idea how to print the stack trace in the logger with Java 1.4?

dalewking said...

The RoboGuice framework includes a logger class that uses this technique to find the class that is making the logging call. It is a logger that requires no configuration (i.e. you don't have to pass a class or string tag to it to tell it which logger it is). All you do is make static method calls.

See the source here: https://github.com/roboguice/roboguice/blob/master/roboguice/src/main/java/roboguice/util/Ln.java

SARAL SAXENA said...

@Javin perfect article ..just want to add what I have added ..

I have a utility method that returns a string with the stacktrace:

static String getStackTrace(Throwable t) {
StringWriter sw = new StringWriter();
PrintWriter pw = new PrintWriter(sw, true);
t.printStackTrace(pw);
pw.flush();
sw.flush();
return sw.toString();
}

And just logit like...

...
catch (FileNotFoundException e) {
logger.config(getStackTrace(e));
}

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