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

@Testpublic 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