Java中典型的内存泄露问题和解决方法
发布时间：2020-12-14 14:19:28 所属栏目：Java 来源：网络整理
导读：Q：在Java中怎么可以产生内存泄露？ A：Java中，造成内存泄露的原因有很多种。典型的例子是一个没有实现hasCode和 equals方法的Key类在HashMap中保存的情况。最后会生成很多重复的对象。所有的内存泄露 最后都会抛出OutOfMemoryError异常，下面通过一段简短
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Q：在Java中怎么可以产生内存泄露？ 复制代码 代码如下: import java.util.HashMap; import java.util.Map; public class MemoryLeak { public static void main(String[] args) { Map<Key,String> map = new HashMap<Key,String>(1000); int counter = 0; while (true) { // creates duplicate objects due to bad Key class map.put(new Key("dummyKey"),"value"); counter++; if (counter % 1000 == 0) { System.out.println("map size: " + map.size()); System.out.println("Free memory after count " + counter + " is " + getFreeMemory() + "MB"); sleep(1000); } } } // inner class key without hashcode() or equals() -- bad implementation static class Key { private String key; public Key(String key) { this.key = key; } } //delay for a given period in milli seconds public static void sleep(long sleepFor) { try { Thread.sleep(sleepFor); } catch (InterruptedException e) { e.printStackTrace(); } } //get available memory in MB public static long getFreeMemory() { return Runtime.getRuntime().freeMemory() / (1024 * 1024); } } 结果如下： 复制代码 代码如下: map size: 1000 Free memory after count 1000 is 4MB map size: 2000 Free memory after count 2000 is 4MB map size: 1396000 Free memory after count 1396000 is 2MB map size: 1397000 Free memory after count 1397000 is 2MB map size: 1398000 Free memory after count 1398000 is 2MB map size: 1399000 Free memory after count 1399000 is 1MB map size: 1400000 Free memory after count 1400000 is 1MB map size: 1401000 Free memory after count 1401000 is 1MB ..... ..... map size: 1452000 Free memory after count 1452000 is 0MB map size: 1453000 Free memory after count 1453000 is 0MB Exception in thread "main" java.lang.OutOfMemoryError: Java heap space at java.util.HashMap.addEntry(HashMap.java:753) at java.util.HashMap.put(HashMap.java:385) at MemoryLeak.main(MemoryLeak.java:10) Q:怎么解决上面的内存泄露？ 复制代码 代码如下: ..... static class Key { private String key; public Key(String key) { this.key = key; } @Override public boolean equals(Object obj) { if (obj instanceof Key) return key.equals(((Key) obj).key); else return false; } @Override public int hashCode() { return key.hashCode(); } } ..... 重新执行程序会得到如下结果： 复制代码 代码如下: map size: 1 Free memory after count 1000 is 4MB map size: 1 Free memory after count 2000 is 4MB map size: 1 Free memory after count 3000 is 4MB map size: 1 Free memory after count 4000 is 4MB ... Free memory after count 73000 is 4MB map size: 1 Free memory after count 74000 is 4MB map size: 1 Free memory after count 75000 is 4MB Q：在实际场景中，你怎么查找内存泄露？ 复制代码 代码如下: C:&;jps 5808 Jps 4568 MemoryLeak 3860 Main 通过命令行打开jconsole 复制代码 代码如下: C:&;jconsole 4568 实现了hasCode和equals的Key类和没有实现的图表如下所示：
造成内存泄露的：
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