JAVA try..catch..finally与return执行顺序研究

之前碰到了这类问题，然后在CSDN上看到了这方面的讲解了，觉得获益匪浅。自己也去实践了一下，稍微分享一下心得。第一次发博，表述错误与不清楚的地方多多包涵。

基本测试

先上测试代码，logger功能可以看成print

@Test
public void tryCatchFinallyTest() {
    Long startTimeMilSec;
    Long endTimeMilSec;
    startTimeMilSec = System.currentTimeMillis();
    logger.info("start test, current time : {}", startTimeMilSec);
    String returnInfo = tryCatchFinallyTestFun().getInfo();
    logger.info("return info : {}", returnInfo);
    endTimeMilSec = System.currentTimeMillis();
    logger.info("end test, current time : {}", endTimeMilSec);
    logger.info("total run time : {} milSec", endTimeMilSec - startTimeMilSec);
}

private TryCatchFinallyTestClass tryCatchFinallyTestFun() {
    TryCatchFinallyTestClass testResult = new TryCatchFinallyTestClass();
    testResult.setInfo("origin text before change");
    try {
        logger.info("start try");
        throw new Exception("test exception");
    } catch (Exception e) {
        logger.info("start catch");
        return testResult;
    } finally {
        logger.info("start finally");
        testResult.setInfo("text change by finally");
        logger.info("end finally");
    }
}

private class TryCatchFinallyTestClass {
    private String info;

    public String getInfo() {
        return info;
    }
    public void setInfo(String info) {
        this.info = info;
    }
}

基本思路：tryCatchFinallyFun()函数会按照try->catch->finally执行，在catch中return（在try中return原理应该一样，就不单独测试了）。在finally中修改return的值（为了防止系统自带类引起意外，建了一个测试类TryCatchFinallyTestClass存返回信息）。tryCatchFinallyTest调用测试函数，然后打印各个阶段的执行信息。测试结果如下：

17:19:41.821 [main] INFO com.study.javaweb.test1.methodTest.JavaMethodTest - start test, current time : 1505467181821
17:19:41.823 [main] INFO com.study.javaweb.test1.methodTest.JavaMethodTest - start try
17:19:41.823 [main] INFO com.study.javaweb.test1.methodTest.JavaMethodTest - start catch
17:19:41.823 [main] INFO com.study.javaweb.test1.methodTest.JavaMethodTest - start finally
17:19:41.823 [main] INFO com.study.javaweb.test1.methodTest.JavaMethodTest - end finally
17:19:41.823 [main] INFO com.study.javaweb.test1.methodTest.JavaMethodTest - return info : text change by finally
17:19:41.823 [main] INFO com.study.javaweb.test1.methodTest.JavaMethodTest - end test, current time : 1505467181823
17:19:41.823 [main] INFO com.study.javaweb.test1.methodTest.JavaMethodTest - total run time : 2 milSec

可以看到执行顺序：主程序->try->catch->finally->return->返回，而且最终返回的值被finally修改了。

进一步地研究一下：

在catch、finally中引发异常对return结果的影响

测试1:

如果在catch中有意引发一个exception会不会影响return的返回？

private TryCatchFinallyTestClass tryCatchFinallyTestFun() {
    TryCatchFinallyTestClass testResult = new TryCatchFinallyTestClass();
    testResult.setInfo("origin text before change");
    try {
        logger.info("start try");
        throw new Exception("test exception");
    } catch (Exception e) {
        logger.info("start catch");
        testResult = new TryCatchFinallyTestClass();
        testResult.getInfo().getBytes();//throws exception here
        logger.info("end catch");
        return testResult;
    } finally {
        logger.info("start finally");
        testResult = new TryCatchFinallyTestClass();
        testResult.setInfo("text changed by finally");
        logger.info("end finally");
    }
}

如果finally中不设置return， 果然抛出异常java.lang.NullPointerException

那我在finally中设置return会怎么样？设置return后结果：

17:51:38.243 [main] INFO com.study.javaweb.test1.methodTest.JavaMethodTest - start test, current time : 1505469098243
17:51:38.245 [main] INFO com.study.javaweb.test1.methodTest.JavaMethodTest - start try
17:51:38.245 [main] INFO com.study.javaweb.test1.methodTest.JavaMethodTest - start catch
17:51:38.245 [main] INFO com.study.javaweb.test1.methodTest.JavaMethodTest - start finally
17:51:38.245 [main] INFO com.study.javaweb.test1.methodTest.JavaMethodTest - end finally
17:51:38.245 [main] INFO com.study.javaweb.test1.methodTest.JavaMethodTest - return info : text changed by finally
17:51:38.245 [main] INFO com.study.javaweb.test1.methodTest.JavaMethodTest - end test, current time : 1505469098245
17:51:38.245 [main] INFO com.study.javaweb.test1.methodTest.JavaMethodTest - total run time : 2 milSec

catch被中断了，但是函数正常返回

测试2：

在catch中return但是在finally中引发异常，会不会影响返回

private TryCatchFinallyTestClass tryCatchFinallyTestFun() {
        TryCatchFinallyTestClass testResult = new TryCatchFinallyTestClass();
        testResult.setInfo("origin text before change");
        try {
            logger.info("start try");
            throw new Exception("test exception");
        } catch (Exception e) {
            logger.info("start catch");
            testResult.setInfo("text changed by catch");
            logger.info("end catch");
            return testResult;
        } finally {
            logger.info("start finally");
//            testResult = new TryCatchFinallyTestClass();
//            testResult.setInfo("text changed by finally");
            testResult = new TryCatchFinallyTestClass();
            testResult.getInfo().getBytes();//throws exception here
            logger.info("end finally");
            return testResult;

        }

} 结果：java.lang.NullPointerException，异常并影响返回

运行环境：http://blog.csdn.net/leean950806/article/details/77994864