Null Pointer Exception while using Java Compiler API

Question

MyClass.java:

package test;
public class MyClass {
    public void myMethod(){
        System.out.println("My Method Called");
    }
}

Listing for SimpleCompileTest.java that compiles the MyClass.java file.

SimpleCompileTest.java:

package test;
import javax.tools.*;
public class SimpleCompileTest {
    public static void main(String[] args) {
String fileToCompile = "test" + java.io.File.separator +"MyClass.java";
JavaCompiler compiler = ToolProvider.getSystemJavaCompiler();
int compilationResult = compiler.run(null, null, null, fileToCompile);
        if(compilationResult == 0){
            System.out.println("Compilation is successful");
        }else{
            System.out.println("Compilation Failed");
        }
    }
}

I am executing the SimpleCompileTest class and getting a NullPointerException. The ToolProvider.getSystemJavaCompiler() is returning null. Can someone tell me what is wrong with the code

Lath

can you please edit your code with tags? – Bastien

So your problem is that ToolProvider.getSystemJavaCompiler() returns null? – Wilmot

Answer 1

I suspect you're running into this problem - running the code with a JRE instead of a JDK.

When you run SimpleCompileTest, try explicitly specifying the version of java.exe you're using as the one in your JDK directory.

Obsess

How do you explicitly specify the version of Java.exe you're using as the one in your JDK? I tried Run As but it already Project JRE selected as the JRE – Satisfied

@Imray: I'm not sure what you're asking - if that's the selected JRE, that's what will run. If you want a different one, select a different JRE. It sounds like you need to ask a new question with your exact problem. – Obsess

In your answer you say: "When you run SimpleCompileTest, try explicitly specifying the version of java.exe you're using as the one in your JDK directory." I'm asking, how do you do that? – Satisfied

@Imray: I'm saying that presumably the "Project JRE" you've got configured is simply not the right one. So edit that configuration. – Obsess

Answer 2

I got the same error. Maybe I am too late to answer this question, but I share my own experiences, it might help someone else facing the same issue in the future. I was playing around with the source code at Compile Java Files At Runtime.

I was getting java.lang.NullPointerException as it is mentioned. I printed out the Java home directory with System.out.println(System.getProperty("java.home"));, and noticed my Eclipse was pointing to "C:\Program Files\Java\jre7" even after I changed my preferences to use JDK1.7 instead of JRE1.7.

I found a workaround by forcing the usage of JDK1.7 by setting system property like this:

System.setProperty("java.home", "C:\\Program Files\\Java\\jdk1.7.0_02");

Then I compiled my program and did not get any NullPointerException.

Bradwell

You are great dear. you have solved my problem of last 3 weeks. thanks – Lalalalage

I tried this to make compilation-toolkit work. I had to use System.setProperty("java.home", "C:\\Program Files\\Java\\jdk1.7.0_02\jre"); to make it work. – Albumen

Answer 3

Probably you have a JRE instead of JDK installed. https://bugs.java.com/bugdatabase/view_bug?bug_id=6477844

Pitsaw

Answer 4

I was having the same problem

JavaCompiler compiler = ToolProvider.getSystemJavaCompiler();

was returning null. Even after using

System.setProperty("java.home", "C:\\Program Files\\Java\\jdk1.8.0_31");

was returning null.

However the issue was simple as this code is in the Tools.jar found in Java\jdk1.8.0_31\lib if you are using JDK. what i did was to go to project-->properties-->Java Build Path-->order and export--> and moved tool.jar to the top of other JRE and projects. This helped me get rid of null hope this help you as well.Happy compiling...:-)

Counterspy

Answer 5

Its working with Java application by expicitily including the tools.jar but for web application not working. Throwing Nullpointer

Valiant

Answer 6

SUPPLEMENT: The answer above is to set the java.home system property within the program. That works for me too, but it's not a very general solution, since you've hard-coded for one jdk version. The alternative that I'm using now is to give the full path to "java" on the command line when I run the program. Such as (consistent with examples above):

C:\\Program Files\Java\jdk1.7.0_02\jre\bin\java -cp ..\classes path.to.program.myProgram

Giving the full path to the jdk version means that's the version that's running the program, so that's the one that will be fetched with ToolProvider.getSystemJavaCompiler();

Suzette