Understanding java.lang.reflect.InvocationTargetException and why it occurs

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Reason for java.lang.reflect.InvocationTargetException
Handle InvocationTargetException

In this post, we will see about java.lang.reflect.InvocationTargetException.

You might get java.lang.reflect.InvocationTargetException while working with reflection in java.

Reason for java.lang.reflect.InvocationTargetException

Reflection layer throws this exception when calling method or constructor throws any exception. java.lang.reflect.InvocationTargetException wraps underlying exception thrown by actual method or constructor call.

Let’s see this with the help of example:
Create a simple class named StringUtils.java. It will have method getLengthOfString() which does not have null handling, so when we pass null to this method, it will throw java.lang.NullPointerException.

package org.arpit.java2blog;

public class StringUtils {

    public int getLengthOfString(String str)
    {
        return str.length();
    }
}

package org.arpit.java2blog;

public class StringUtils {

public int getLengthOfString(String str)

{

return str.length();

}

Create anther class to call getLengthOfString using reflection.

package org.arpit.java2blog;

import java.lang.reflect.InvocationTargetException;
import java.lang.reflect.Method;

public class ReflectionMain {

    public static void main(String[] args) {
        StringUtils su=new StringUtils();

        try {
            Class[] paramString = new Class[1];
            paramString[0] = String.class;
            Method method=StringUtils.class.getMethod("getLengthOfString",paramString);
            String str=null;
            Object len = method.invoke(su, str);
            System.out.println(len);
        } catch (NoSuchMethodException | SecurityException | IllegalAccessException | IllegalArgumentException | InvocationTargetException e) {
            e.printStackTrace();
        }
    }
}

package org.arpit.java2blog;

import java.lang.reflect.InvocationTargetException;

import java.lang.reflect.Method;

public class ReflectionMain {

public static void main(String[] args) {

StringUtils su=new StringUtils();

try {

Class[] paramString = new Class[1];

paramString[0] = String.class;

Method method=StringUtils.class.getMethod("getLengthOfString",paramString);

String str=null;

Object len = method.invoke(su, str);

System.out.println(len);

} catch (NoSuchMethodException | SecurityException | IllegalAccessException | IllegalArgumentException | InvocationTargetException e) {

e.printStackTrace();

}

Output:

java.lang.reflect.InvocationTargetException
at java.base/jdk.internal.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
at java.base/jdk.internal.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
at java.base/jdk.internal.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
at java.base/java.lang.reflect.Method.invoke(Method.java:567)
at org.arpit.java2blog.ReflectionMain.main(ReflectionMain.java:16)
Caused by: java.lang.NullPointerException
at org.arpit.java2blog.StringUtils.getLengthOfString(StringUtils.java:7)
… 5 more

As you can see, we are getting java.lang.reflect.InvocationTargetException exception because of underlying NullPointerException.

Reflection layer wraps java.lang.reflect.InvocationTargetException around actual Exception to demostrate that this exception was raised during reflection API call.

Handle InvocationTargetException

As underlying exception is actual cause of InvocationTargetException, we can use Throwable's getCause() method to get actual underlyting exception and use it to log or rethrow the exception.

package org.arpit.java2blog;

import java.lang.reflect.InvocationTargetException;
import java.lang.reflect.Method;

public class ReflectionMain {

    public static void main(String[] args) {
        StringUtils su=new StringUtils();

        try {
            Class[] paramString = new Class[1];
            paramString[0] = String.class;
            Method method=StringUtils.class.getMethod("getLengthOfString",paramString);
            String str=null;
            Object len = method.invoke(su, str);
            System.out.println(len);
        } catch (NoSuchMethodException | SecurityException | IllegalAccessException | IllegalArgumentException | InvocationTargetException e) {
            Throwable actualException = e.getCause();
            actualException.printStackTrace();
        }
    }
}

package org.arpit.java2blog;

import java.lang.reflect.InvocationTargetException;

import java.lang.reflect.Method;

public class ReflectionMain {

public static void main(String[] args) {

StringUtils su=new StringUtils();

try {

Class[] paramString = new Class[1];

paramString[0] = String.class;

Method method=StringUtils.class.getMethod("getLengthOfString",paramString);

String str=null;

Object len = method.invoke(su, str);

System.out.println(len);

} catch (NoSuchMethodException | SecurityException | IllegalAccessException | IllegalArgumentException | InvocationTargetException e) {

Throwable actualException = e.getCause();

actualException.printStackTrace();

}

java.lang.NullPointerException
at org.arpit.java2blog.StringUtils.getLengthOfString(StringUtils.java:7)
at java.base/jdk.internal.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
at java.base/jdk.internal.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
at java.base/jdk.internal.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
at java.base/java.lang.reflect.Method.invoke(Method.java:567)
at org.arpit.java2blog.ReflectionMain.main(ReflectionMain.java:16)

To resolve InvocationTargetException, you need to solve underlying Exception(NullPointerException) in above example.
Let’s handle the null check in StringUtils.java class and you won’t get any exception anymore.

package org.arpit.java2blog;

public class StringUtils {

    public int getLengthOfString(String str) {
        if (str != null) {
            return str.length();
        } else
            return 0;
    }

}

package org.arpit.java2blog;

public class StringUtils {

public int getLengthOfString(String str) {

if (str != null) {

return str.length();

} else

return 0;

}

Now when we run ReflectionMain.java again, you will see below output:

That’s all about java.lang.reflect.InvocationTargetException in java.

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Understanding java.lang.reflect.InvocationTargetException and why it occurs

Reason for java.lang.reflect.InvocationTargetException

Handle InvocationTargetException

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Handle InvocationTargetException

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