JAVA OOM内存溢出问题深入解析

/**
 * 栈溢出
 */
public class Stack {
    public static void main(String[] args) {
        new Stack().test();
    }
    public void test() {
        test();
    }
}

import java.util.ArrayList;
import java.util.List;
public class HeapOOMTest {
    public static void main(String[] args) {
        List<byte[]> list = new ArrayList<>();
        try {
            while (true) {
                // 分配大量的内存，每次分配1MB的字节数组
                byte[] data = new byte[1024 * 1024]; // 1MB
                list.add(data);
            }
        } catch (OutOfMemoryError e) {
            System.out.println("发生堆溢出错误：Java heap space");
            e.printStackTrace();
        }
    }
}

import java.util.List;
import java.util.ArrayList;
import java.nio.file.*;
import java.io.IOException;
public class PermGenOutOfMemory {
    public static void main(String[] args) {
        List<Class<?>> classes = new ArrayList<>();
        try {
            while (true) {
                // Generate a unique class name and bytecode
                String className = "DynamicClass" + System.nanoTime();
                byte[] classData = generateClassBytes(className);
                // Define the class by writing it to a file and loading it
                Path classFilePath = Paths.get(className + ".class");
                Files.write(classFilePath, classData);
                Class<?> clazz = loadClass(className, classFilePath);
                classes.add(clazz);
                // Optional: Delete the class file after loading
                Files.delete(classFilePath);
            }
        } catch (OutOfMemoryError | IOException e) {
            System.out.println("OutOfMemoryError: Metaspace");
            e.printStackTrace();
        }
    }
    static byte[] generateClassBytes(String className) {
        // Replace this with your own class bytecode generation logic
        // You can use libraries like ASM for bytecode generation
        // For simplicity, let's just create a class with a single method
        String classContent = "public class " + className + " { public void doSomething() { System.out.println(\"Hello from " + className + "\"); } }";
        return classContent.getBytes();
    }
    static Class<?> loadClass(String className, Path classFilePath) throws IOException {
        // Load the class from the file into the Metaspace
        byte[] classData = Files.readAllBytes(classFilePath);
        return new CustomClassLoader().loadClass(className, classData);
    }
    static class CustomClassLoader extends ClassLoader {
        public Class<?> loadClass(String name, byte[] classData) {
            return defineClass(name, classData, 0, classData.length);
        }
    }
}

import sun.misc.Unsafe;
import java.lang.reflect.Field;
public class DirectMemoryOOMTest {
    public static void main(String[] args) {
        int i = 0;
        long allocatedMemory = 0;
        Unsafe unsafe = null;
        try {
            Field field = Unsafe.class.getDeclaredFields()[0];
            field.setAccessible(true);
            unsafe = (Unsafe) field.get(null);
            while (true) {
                long memory = 1024 * 1024;
                allocatedMemory += memory;
                unsafe.allocateMemory(memory);
                i++;
            }
        } catch (Exception e) {
            e.printStackTrace();
         } 
    }
}