For some reason the premain of my Java Agent is executed twice when I run a program inside of IDEA and add the Agent jar via the IDEA VM options:
I have the following sample program and added the Java Agent in IDEA via
Run Configuration -> VM options: -javaagent:/path/to/agent/MyJavaAgent.jar
package com.example;
public class Test {
public static void main(String[] args) {
System.out.println("Hello World!");
}
}
The MyJavaAgent.jar has the following structure:
.
├── com
│ └── example
│ └── MyJavaAgent.class
└── META-INF
└── MANIFEST.MF
MyJavaAgent.java
package com.example;
import java.lang.instrument.Instrumentation;
public class MyJavaAgent {
private static int callCount = 0;
public static void premain(String agentArgs, Instrumentation inst) {
callCount++;
System.out.println("premain call " + callCount);
}
}
MANIFEST.MF
Manifest-Version: 1.0
Premain-Class: com.example.MyJavaAgent
Can-Redefine-Classes: true
Can-Retransform-Classes: true
Can-Set-Native-Method-Prefix: true
When I run the sample Test.main() I get the following output:
> Task :Test.main()
premain call 1
premain call 2
Hello World!
When I run the program without IDEA everything looks like expected:
> java -javaagent:/path/to/agent/MyJavaAgent.jar com.example.Test
premain call 1
Hello World!
Can someone explain what is happening here? Is that an IDEA bug?
I'm using IntelliJ IDEA 2019.3.4 (Ultimate Edition), Build #UI-193.6911.18
