在异常情况下执行 try 块中的剩余代码

Question

我有以下代码：

try{
  line1; // can throw exception
  line2; // can throw exception
  line3; // can throw exception
  line4; // can throw exception
}catch(Exception e){
   handle exception;
}finally{
  do remaining stuffs;
}

即使上面的行出现异常，我也需要在 try 块中执行所有 4 行。

假设代码在 try 块的 line2 中遇到了异常，即使这样我也需要执行 line3 和 line4（这反过来又会抛出异常）。有没有一种简单的方法可以做到这一点，而不是使用多个 try-catch 块。

Answer 1

如果有意义的话，您可以在外部 try/catch 块中包含 try/catch 块。像这样的：

try{
  line1; // can throw exception
  try {
    line2; // can throw exception
  } catch (Exception e) {
    if (e is a really bad one) throw e;  // don't continue
    else System.out.println("line2 failed but I'll keep going");
  }
  try {
    line3; // can throw exception
  } catch (Exception e) {
    if (e is a really bad one) throw e;  // don't continue
    else System.out.println("line3 failed but I'll keep going");
  }
  line4; // can throw exception
}catch(Exception e){
   handle exception;
}finally{
  do remaining stuffs;
}

Answer 2

try with resource 语句允许指定即使在例外情况下也应执行的操作，语法简洁（与嵌套的finally 块相比）。它还有另一个优点：当多个操作失败时，异常不会相互影响，而是在主 throwable 上注册为 suppressed throwables。一个缺点是资源的关闭顺序与它们创建时的顺序相反，因此我们必须颠倒这些行的顺序：

public static void main(String[] args) {
    for(int test = 0; test < 16; test++) {
        int currentTest = test;
        System.out.println("Test "+currentTest);

        try(AutoCloseable c1 = () -> line4(currentTest);   // 4
            AutoCloseable c2 = () -> line3(currentTest);   // 3
            AutoCloseable c3 = () -> line2(currentTest)) { // 2
            line1(currentTest);                            // 1
        }
        catch(Exception ex) {
            System.out.print("got exception ");
            ex.printStackTrace(System.out);
        }

        System.out.println();
    }
}
public static void line1(int whichTest) {
    if((whichTest & 1) != 0) {
        System.out.println("letting line 1 fail");
        throw new RuntimeException("line 1 failed");
    } else System.out.println("line1 executed");
}
public static void line2(int whichTest) {
    if((whichTest & 2) != 0) {
        System.out.println("letting line 2 fail");
        throw new RuntimeException("line 2 failed");
    } else System.out.println("line2 executed");
}
public static void line3(int whichTest) {
    if((whichTest & 4) != 0) {
        System.out.println("letting line 3 fail");
        throw new RuntimeException("line 3 failed");
    } else System.out.println("line3 executed");
}
public static void line4(int whichTest) {
    if((whichTest & 8) != 0) {
        System.out.println("letting line 4 fail");
        throw new RuntimeException("line 4 failed");
    } else System.out.println("line4 executed");
}

这个示例程序贯穿所有可能的场景。我缩短了输出以仅显示一些示例：

Test 0
line1 executed
line2 executed
line3 executed
line4 executed

Test 1
letting line 1 fail
line2 executed
line3 executed
line4 executed
got exception java.lang.RuntimeException: line 1 failed
    at SafeActions.line1(SafeActions.java:23)
    at SafeActions.main(SafeActions.java:10)

Test 9
letting line 1 fail
line2 executed
line3 executed
letting line 4 fail
got exception java.lang.RuntimeException: line 1 failed
    at SafeActions.line1(SafeActions.java:23)
    at SafeActions.main(SafeActions.java:10)
    Suppressed: java.lang.RuntimeException: line 4 failed
        at SafeActions.line4(SafeActions.java:41)
        at SafeActions.lambda$main$0(SafeActions.java:7)
        at SafeActions.main(SafeActions.java:7)

Test 15
letting line 1 fail
letting line 2 fail
letting line 3 fail
letting line 4 fail
got exception java.lang.RuntimeException: line 1 failed
    at SafeActions.line1(SafeActions.java:23)
    at SafeActions.main(SafeActions.java:10)
    Suppressed: java.lang.RuntimeException: line 2 failed
        at SafeActions.line2(SafeActions.java:29)
        at SafeActions.lambda$main$2(SafeActions.java:9)
        at SafeActions.main(SafeActions.java:7)
    Suppressed: java.lang.RuntimeException: line 3 failed
        at SafeActions.line3(SafeActions.java:35)
        at SafeActions.lambda$main$1(SafeActions.java:8)
        at SafeActions.main(SafeActions.java:7)
    Suppressed: java.lang.RuntimeException: line 4 failed
        at SafeActions.line4(SafeActions.java:41)
        at SafeActions.lambda$main$0(SafeActions.java:7)
        at SafeActions.main(SafeActions.java:7)

直接使用AutoCloseable 接口的一个缺点是它声明可能会抛出Exception，因此迫使我们捕获Exception。如果动作没有抛出检查异常或非常特定的类型，创建自己的扩展AutoCloseable 的函数接口很有用（如果是IOException，已经有java.io.Closeable）。

interface MyAction extends AutoCloseable {
    @Override public void close();
}    
public static void main(String[] args) {
    int currentTest = 11;

    try(MyAction c1 = () -> line4(currentTest);
        MyAction c2 = () -> line3(currentTest);
        MyAction c3 = () -> line2(currentTest)) {
        line1(currentTest);
    }
}

由于这个示例没有捕获异常，我还删除了在第二次迭代之后不会执行的循环。

letting line 1 fail
letting line 2 fail
line3 executed
letting line 4 fail
Exception in thread "main" java.lang.RuntimeException: line 1 failed
    at SafeActions.line1(SafeActions.java:17)
    at SafeActions.main(SafeActions.java:11)
    Suppressed: java.lang.RuntimeException: line 2 failed
        at SafeActions.line2(SafeActions.java:23)
        at SafeActions.lambda$main$2(SafeActions.java:10)
        at SafeActions.main(SafeActions.java:8)
    Suppressed: java.lang.RuntimeException: line 4 failed
        at SafeActions.line4(SafeActions.java:35)
        at SafeActions.lambda$main$0(SafeActions.java:8)
        at SafeActions.main(SafeActions.java:8)