Java中多層異常包裹時候獲取最底層的最真實異常-分析Java異常棧

示例代碼：

import java.util.concurrent.Callable;
import java.util.concurrent.ExecutorService;
import java.util.concurrent.Executors;
import java.util.concurrent.Future;

class AudienceLimitExcption extends Exception {
    public AudienceLimitExcption(String message, Throwable cause) {
        super(message, cause);
    }
}

class Task implements Callable {

    @Override
    public Object call() throws Exception {
        try {
            System.out.println(1 / 0);
        } catch (Exception e) {

            throw new AudienceLimitExcption("limit error", e);
        }

        return 1;
    }
}

 

代碼異常1：

public class Main {

    public static void main(String[] args) {
        Object r = null;
        ExecutorService es = Executors.newFixedThreadPool(4);
        try {
            Future f = es.submit(new Task());
            r = f.get();
            System.out.println();
        } catch (Throwable e) {
            System.out.println(e.getClass());
        }
    }
}

輸出結果：class java.util.concurrent.ExecutionException  不是最真實的底層拋出去的異常。

分析異常棧：

會發現當cause==當前異常時候就是最真實異常，於是代碼如下：

public class Main {

    public static void main(String[] args) {
        Object r = null;
        ExecutorService es = Executors.newFixedThreadPool(4);
        try {
            Future f = es.submit(new Task());
            r = f.get();
            System.out.println();
        } catch (Throwable e) {
            while (e != null) {
                Throwable cause = e.getCause();
                if (e.equals(cause)) {
                    System.out.println(e);
                }
                e = cause;
            }
        }
    }
}

運行發現沒有輸出，debug發現當e爲真實異常時候，e.getCause方法返回值爲null。因此if分支無法爲true，所以沒有輸出。與上圖異常棧分析結論相悖，只能查看一下getCause方法實現：

    public synchronized Throwable getCause() {
        return (cause==this ? null : cause);
    }

JDK實現時候，當cause等於當前異常e時候直接返回null，因此正確方案如下：

public class Main {

    public static void main(String[] args) {
        Object r = null;
        ExecutorService es = Executors.newFixedThreadPool(4);
        try {
            Future f = es.submit(new Task());
            r = f.get();
            System.out.println();
        } catch (Throwable e) {
            while (e != null) {
                Throwable cause = e.getCause();
                if (cause == null) {
                    System.out.println(e.getClass());
                }
                e = cause;
            }
        }
    }
}

輸出結果也就是1/0最真實的異常類型：class java.lang.ArithmeticException