java - 如何预测 java.lang.OutOfMemory 异常？

Question

是否可以通过编程方式实现？

这是我尝试过的:

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

public class TestMemory {

    public static void main(String[] args) {

        int kb = 1024;

        //Getting the runtime reference from system
        Runtime runtime = Runtime.getRuntime();

        //Print used memory
        System.out.println("Used Memory:" + (runtime.totalMemory() - runtime.freeMemory()) / kb);

        //Print free memory
        System.out.println("Free Memory:" + runtime.freeMemory() / kb);

        //Print total available memory
        System.out.println("Total Memory:" + runtime.totalMemory() / kb);

        //Print Maximum available memory
        System.out.println("Max Memory:" + runtime.maxMemory() / kb);

        List<String> list = new ArrayList<>();
        for (int i = 0; i < 10000; i++) {
            for (int j = 0; j < 1000; j++) {
                list.add("abcdefghij" + i + j);
            }
            if (i % 1000 == 0) {
                try {
                    Thread.sleep(500);
                    System.out.println("Free Memory:" + runtime.freeMemory() / kb + " Kb");
                } catch (InterruptedException e) {
                    // TODO Auto-generated catch block
                    e.printStackTrace();
                }
            }
        }
    }
}

和输出:

Used Memory:289
Free Memory:15582
Total Memory:15872
Max Memory:126720
Free Memory:15405 Kb
Free Memory:22820 Kb (long pause, longer than 500ms and then exception)
Exception in thread "main" java.lang.OutOfMemoryError: Java heap space
    at java.util.Arrays.copyOfRange(Arrays.java:2694)
    at java.lang.String.<init>(String.java:203)
    at java.lang.StringBuilder.toString(StringBuilder.java:405)
    at TestMemory.main(TestMemory.java:32)

这对我来说意义不大。我希望“可用内存”值在崩溃前减少。如何编写一个循环检查可用内存并在出现此异常之前通知我内存量？

Answer 1

我不认为尝试管理您自己的程序以避免 OutOfMemoryException 是一种好方法。您必须在堆之前调整大小以满足您的内存需求。无论如何对我来说你的代码是正确的但你需要调用 GC:System.gc() 在调用 runtime.freeMemory() 之前。

 if (i % 1000 == 0) {
            try {
                System.gc();
                Thread.sleep(500);
                System.out.println("Free Memory:" + runtime.freeMemory() / kb + " Kb");
            } catch (InterruptedException e) {
                // TODO Auto-generated catch block
                e.printStackTrace();
            }
        }