2.Java記憶體溢位程式舉例

OutOfMemoryError: Java heap space

import java.util.ArrayList;
import java.util.List;

/**
-Xms20M -Xmx20M -XX:+HeapDumpOnOutOfMemoryError
**/
public class JVMTest {
	
	static class OOM{}
	
	public static void main(String[] args) {
		List<OOM> list = new ArrayList<OOM>();
		while(true){
			list.add(new OOM());
		}
	}
}
 

列印結果：

java.lang.OutOfMemoryError: Java heap space Dumping heap to java_pid1948.hprof … Heap dump file created [27965238 bytes in 0.084 secs] Exception in thread “main” java.lang.OutOfMemoryError: Java heap space at java.util.Arrays.copyOf(Arrays.java:3210) at java.util.Arrays.copyOf(Arrays.java:3181) at java.util.ArrayList.grow(ArrayList.java:261) at java.util.ArrayList.ensureExplicitCapacity(ArrayList.java:235) at java.util.ArrayList.ensureCapacityInternal(ArrayList.java:227) at java.util.ArrayList.add(ArrayList.java:458) at JVMTest.main(JVMTest.java:11)

生成的.hprof檔案預設在對應工程下面。可以使用如下語句來指定生成的.hprof檔案路徑及在遇到OnOutOfMemoryError時執行的linux命令。

-XX:+HeapDumpOnOutOfMemoryError -XX:HeapDumpPath=/tmp/heapdump.hprof -XX:OnOutOfMemoryError =“sh ~/cleanup.sh”

StackOverflowError

/**
 * 
 * @author x
 * -Xss128K
 */
public class JVMTest {
	
	private int stackLength = 1;
	public void stackLeak(){
		stackLength++;
		stackLeak();
	}
	
	public static void main(String[] args) {
		JVMTest jvmTest = new JVMTest();
		try {
			jvmTest.stackLeak();
		} catch (Exception e) {
			System.out.println("Stack length:" + jvmTest.stackLength);
			throw(e);
		}
	}
}
 

列印結果：

Exception in thread “main” java.lang.StackOverflowError at JVMTest.stackLeak(JVMTest.java:13) at JVMTest.stackLeak(JVMTest.java:14) at JVMTest.stackLeak(JVMTest.java:14) at JVMTest.stackLeak(JVMTest.java:14) at JVMTest.stackLeak(JVMTest.java:14) at JVMTest.stackLeak(JVMTest.java:14) at JVMTest.stackLeak(JVMTest.java:14)

OutOfMemoryError: Metaspace

import java.util.ArrayList;
import java.util.List;

/**
 * 
 * @author x
 * -XX:MaxMetaspaceSize=512K -XX:MetaspaceSize=512K
 */
public class JVMTest {
	public static void main(String[] args) {
		List<String> list = new ArrayList<String>();
		int  i = 0;
		while(true){
			list.add(String.valueOf(i++).intern());
		}
	}
}

列印

Error occurred during initialization of VM OutOfMemoryError: Metaspace

java.lang.OutOfMemoryError 本地記憶體

import java.lang.reflect.Field;
import sun.misc.Unsafe;

/**
 * VM Args: -Xmx20M -XX:MaxDirectMemorySize=10M
 * @author x
 */
public class DirectMemoryOOM {
	private static final int _1MB = 1024 * 1024;
	
	@SuppressWarnings("restriction")
	public static void main(String[] args) throws IllegalArgumentException, IllegalAccessException {
		Field unsafeField = Unsafe.class.getDeclaredFields()[0];
		unsafeField.setAccessible(true);
		Unsafe unsafe = null;
		unsafe = (Unsafe) unsafeField.get(null);
		while (true){
			unsafe.allocateMemory(_1MB);
		}
	}
}

列印結果：

Exception in thread “main” java.lang.OutOfMemoryError at sun.misc.Unsafe.allocateMemory(Native Method) at DirectMemoryOOM.main(DirectMemoryOOM.java:18)

本地記憶體溢位一個明顯的特徵是在Heap Dump檔案中不會看見明顯的異常，如果發現OOM之後Dump檔案很小，而程式中直接或間接使用了NIO，那就可以考慮檢查一下是否是這方面的原因導致。