java 使用-XX：MaxMetaspaceSize测试元空间的限制，并动态生成许多类以查看它何时中断。

Posted 2021-05-08

package com.company;

import javax.tools.JavaCompiler;
import javax.tools.StandardJavaFileManager;
import javax.tools.StandardLocation;
import javax.tools.ToolProvider;
import java.io.File;
import java.io.FileWriter;
import java.io.IOException;
import java.lang.reflect.InvocationTargetException;
import java.lang.reflect.Method;
import java.util.Collections;

/**
 * This program will generate 1000 classes.
 * It's "useful" to test the limit of the Metaspace using -XX:MaxMetaspaceSize.
 *
 * Start program with :
 * java -Djava.home="C:\Program Files\Java\jdk1.8.0_60\jre" -XX:MaxMetaspaceSize=10m -classpath "C:\wip\test\out\production\test" com.company.TestMetaspaceLimit
 *
 * - java.home : by default, it's without \jre, and `ToolProvider.getSystemJavaCompiler()` returns null.
 * - the classpath should be the same as the CLASS_OUTPUT location given in the program (where the .class are).
 *
 * With 10m of metaspace, it crashes at HelloWorld 304. :-)
 */
public class TestMetaspaceLimit {

    public static void main(String... args) throws Exception {
        for (int i = 0; i < 1000; i++) {
            createClass(i);
        }
    }

    public static void createClass(int i) throws Exception {
        File sourceFile   = new File("Hello" + i + ".java");
        FileWriter writer = new FileWriter(sourceFile);
        writer.write("public class Hello" + i + " { public void talk() { System.out.println(\"Hello world " + i + "\"); } }");
        writer.close();

        // Compile the file
        JavaCompiler compiler = ToolProvider.getSystemJavaCompiler();
        StandardJavaFileManager fileManager = compiler.getStandardFileManager(null, null, null);
        fileManager.setLocation(StandardLocation.CLASS_OUTPUT, Collections.singletonList(new File("C:\\wip\\test\\out\\production\\test")));
        compiler.getTask(null, fileManager, null, null, null, fileManager.getJavaFileObjectsFromFiles(Collections.singletonList(sourceFile))).call();
        fileManager.close();

        // delete the source file
        sourceFile.deleteOnExit();

        makeItTalk(i);
    }

    public static void makeItTalk(int i) throws Exception {
        Class<?> klass = Class.forName("Hello" + i);
        Method thisMethod = klass.getDeclaredMethod("talk");
        thisMethod.invoke(klass.newInstance());
    }
}