【Java异常】Throwable之getCause()

Throwable - getCause()

1 定义

the cause of this throwable or null if the cause is nonexistent or unknown.

返回引起此异常的原因或者 null (不存在原因或者未知情况)。

2 举例

public class Throwable$getCauseTest {
    public static void main(String[] args) {
        getCause1();
        getCause2();
    }

    public static void getCause1() {
        try {
            throw new RuntimeException("main error!");
        } catch (Exception e) {
            System.out.println(e.getCause() instanceof RuntimeException);
            System.out.println("e：" + e + "; e.getCause()：" + e.getCause());
        }
    }

    public static void getCause2() {

        Runnable r1 = () -> {
            throw new RuntimeException("Thread error!");
        };

        Future<Integer> task = Executors.newSingleThreadExecutor().submit(r1, 1);

        try {
            task.get();
        } catch (Exception e) {
            System.out.println(e.getCause() instanceof RuntimeException);
            System.out.println("e：" + e + "; e.getCause()：" + e.getCause());
        }
    }
}

// 输出结果
false
e：java.lang.RuntimeException: main error!; e.getCause()：null
    
true
e：java.util.concurrent.ExecutionException: java.lang.RuntimeException: Thread error!;
e.getCause()：java.lang.RuntimeException: Thread error!

3 总结

• 例如线程池抛出的异常，最外层是 ExecutionException，所以 getCause() 能够获取到里层 RuntimeException；

• 直接捕获抛出的异常，调用 getCause() 则返回的 null；

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感谢阅读，下次再见。ヾ(￣▽￣)Bye_Bye！