java - "Failed to load Premain-Class manifest attribute"尝试使用 java 代理获取对象的大小时

Question

当我尝试运行 java 程序 (java -javaagent:size.jar ObjectSizeTest) 时，出现以下错误:

Failed to load Premain-Class manifest attribute from D:\workspace\ObjectSizeTest\size.jar
Error occurred during initialization of VM
agent library failed to init: instrument

这是 ObjectSizeTest 的代码:

public class ObjectSizeTest {
    public static void main(String[] args) {
        String s = new String("sai");
        System.out.println(ObjectSizeFetcher.getObjectSize(s));
    }
}

MANIFEST.MF(对于 size.jar):

Manifest-Version: 1.0
Created-By: 1.5.0_18 (Sun Microsystems Inc.)

Premain-Class: ObjectSizeFetcher

这是 ObjectSizeFetcher 的代码:

import java.lang.instrument.Instrumentation;

public class ObjectSizeFetcher {
    private static Instrumentation instrumentation;

    public static void premain(String args, Instrumentation inst) {
        instrumentation = inst;
    }

    public static long getObjectSize(Object o) {
        return instrumentation.getObjectSize(o);
    }
}

Answer 1

确保您已提供包含 pre-main 方法的类的完整 java 路径。例如像这样的 org.eclipse.anotherpckg.ObjectSizeFetcher。其次，名称前必须有一个空格，最后要有回车符。例如

Manifest-Version: 1.0
Created-By: 1.5.0_18 (Sun Microsystems Inc.)
Premain-Class: org.eclipse.package.ObjectSizeFetcher

最后一行是由于回车。