java detach java detach方法

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mob64ca13f587aa 2023-09-20 17:03:40

文章标签 java detach catch throw Exception 异常 文章分类 Java 后端开发

一、问题

最近，简单研究了下Exception的一些问题，现总结如下；

二、分析

首先，我想说的是，catch异常和throw异常；

throw是抛出异常，往哪里抛？往上层抛。上层是哪里？哪个调用我的这个方法，我就抛给谁；
catch是方法内抓取异常，然后处理；当然，处理的方法，也包含往上抛，或者说往外抛；

我们先来看一段代码：

import org.junit.Test;

import java.text.ParseException;
import java.text.SimpleDateFormat;
import java.util.Date;

/**
 * @author Auther
 * @title: TestException
 * @projectName generatorSqlmapCustom
 * @description: TODO
 * @date 27/03/201909:50
 */
public class TestException {

    @Test
    public void testTryCatch(){
        try {
            getRead();
        }catch (Exception e){
            e.printStackTrace();
            System.out.println("顶层：");
        }
    }


    public static void getRead() {
        SimpleDateFormat dateFormat = new SimpleDateFormat("yyyy-MM-dd");
        try {
            Date date = dateFormat.parse("2018-1a 3-01");
            System.out.println("date:"+date);
        } catch (ParseException e) {
            e.printStackTrace();
            System.out.println("【解析异常】");
        }catch (Exception e) {
            System.out.println("【异常】");
            //throw new Exception();
        }
    }
}

1、这里，我们写了一个测试方法，一个静态方法；测试方法作为父方法，调用子静态方法；
我们看到，子静态方法解析日期格式时，可能会有【解析异常】（ParseExcetpion）,所以，我们通过catch来抓取异常，并且，抓取异常是有顺序要求的，范围小的要写在前面（上面），越大的，写的越靠后，从上而下，一层层筛异常；因为Exception是所有异常的父类，他可以拦截所有的异常，如果把Exception作为catch的第一项，则后面具体的异常将无法匹配到；测试结果如下：

【解析异常】
java.text.ParseException: Unparseable date: "2018-1a 3-01"
	at java.text.DateFormat.parse(DateFormat.java:366)
	at TestException.getRead(TestException.java:33)
	at TestException.testTryCatch(TestException.java:22)
	at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
	at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
	at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
	at java.lang.reflect.Method.invoke(Method.java:498)
	at org.junit.runners.model.FrameworkMethod$1.runReflectiveCall(FrameworkMethod.java:50)
	at org.junit.internal.runners.model.ReflectiveCallable.run(ReflectiveCallable.java:12)
	at org.junit.runners.model.FrameworkMethod.invokeExplosively(FrameworkMethod.java:47)
	at org.junit.internal.runners.statements.InvokeMethod.evaluate(InvokeMethod.java:17)
	at org.junit.runners.ParentRunner.runLeaf(ParentRunner.java:325)
	at org.junit.runners.BlockJUnit4ClassRunner.runChild(BlockJUnit4ClassRunner.java:78)
	at org.junit.runners.BlockJUnit4ClassRunner.runChild(BlockJUnit4ClassRunner.java:57)
	at org.junit.runners.ParentRunner$3.run(ParentRunner.java:290)
	at org.junit.runners.ParentRunner$1.schedule(ParentRunner.java:71)
	at org.junit.runners.ParentRunner.runChildren(ParentRunner.java:288)
	at org.junit.runners.ParentRunner.access$000(ParentRunner.java:58)
	at org.junit.runners.ParentRunner$2.evaluate(ParentRunner.java:268)
	at org.junit.runners.ParentRunner.run(ParentRunner.java:363)
	at org.junit.runner.JUnitCore.run(JUnitCore.java:137)
	at com.intellij.junit4.JUnit4IdeaTestRunner.startRunnerWithArgs(JUnit4IdeaTestRunner.java:68)
	at com.intellij.rt.execution.junit.IdeaTestRunner$Repeater.startRunnerWithArgs(IdeaTestRunner.java:47)
	at com.intellij.rt.execution.junit.JUnitStarter.prepareStreamsAndStart(JUnitStarter.java:242)
	at com.intellij.rt.execution.junit.JUnitStarter.main(JUnitStarter.java:70)

Process finished with exit code 0

2、接下来，我们把所有的异常都catch住，然后再抛出去，为什么不直接throw呢？其实可以直接抛的，这么做是为了打印下日志，让大家看的更清楚，子方法被那个catch抓住了；代码如下：

import org.junit.Test;

import java.text.ParseException;
import java.text.SimpleDateFormat;
import java.util.Date;

/**
 * @author Auther
 * @title: TestException
 * @projectName generatorSqlmapCustom
 * @description: TODO
 * @date 27/03/201909:50
 */
public class TestException {

    @Test
    public void testTryCatch(){
        try {
            getRead();
        }catch (ParseException e){
            e.printStackTrace();
            System.out.println("【顶层解析异常】");
        }catch (Exception e){
            e.printStackTrace();
            System.out.println("【顶层异常】");
        }
    }


    public static void getRead() throws Exception,ParseException {
        SimpleDateFormat dateFormat = new SimpleDateFormat("yyyy-MM-dd");
        try {
            Date date = dateFormat.parse("2018-1a 3-01");
            System.out.println("date:"+date);
        } catch (ParseException e) {
            e.printStackTrace();
            System.out.println("【解析异常】");
            throw new ParseException("解析异常",e.getErrorOffset());
        }catch (Exception e) {
            System.out.println("【异常】");
            throw new Exception();
        }
    }
}

console控制台输出信息：

【解析异常】
java.text.ParseException: Unparseable date: "2018-1a 3-01"
【顶层解析异常】

	at java.text.DateFormat.parse(DateFormat.java:366)
	at TestException.getRead(TestException.java:33)
	at TestException.testTryCatch(TestException.java:19)
	at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
	at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
	at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
	at java.lang.reflect.Method.invoke(Method.java:498)
	at org.junit.runners.model.FrameworkMethod$1.runReflectiveCall(FrameworkMethod.java:50)
	at org.junit.internal.runners.model.ReflectiveCallable.run(ReflectiveCallable.java:12)
	at org.junit.runners.model.FrameworkMethod.invokeExplosively(FrameworkMethod.java:47)
	at org.junit.internal.runners.statements.InvokeMethod.evaluate(InvokeMethod.java:17)
	at org.junit.runners.ParentRunner.runLeaf(ParentRunner.java:325)
	at org.junit.runners.BlockJUnit4ClassRunner.runChild(BlockJUnit4ClassRunner.java:78)
	at org.junit.runners.BlockJUnit4ClassRunner.runChild(BlockJUnit4ClassRunner.java:57)
	at org.junit.runners.ParentRunner$3.run(ParentRunner.java:290)
	at org.junit.runners.ParentRunner$1.schedule(ParentRunner.java:71)
	at org.junit.runners.ParentRunner.runChildren(ParentRunner.java:288)
	at org.junit.runners.ParentRunner.access$000(ParentRunner.java:58)
	at org.junit.runners.ParentRunner$2.evaluate(ParentRunner.java:268)
	at org.junit.runners.ParentRunner.run(ParentRunner.java:363)
	at org.junit.runner.JUnitCore.run(JUnitCore.java:137)
	at com.intellij.junit4.JUnit4IdeaTestRunner.startRunnerWithArgs(JUnit4IdeaTestRunner.java:68)
	at com.intellij.rt.execution.junit.IdeaTestRunner$Repeater.startRunnerWithArgs(IdeaTestRunner.java:47)
	at com.intellij.rt.execution.junit.JUnitStarter.prepareStreamsAndStart(JUnitStarter.java:242)
	at com.intellij.rt.execution.junit.JUnitStarter.main(JUnitStarter.java:70)
java.text.ParseException: 解析异常
	at TestException.getRead(TestException.java:38)
	at TestException.testTryCatch(TestException.java:19)
	at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
	at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
	at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
	at java.lang.reflect.Method.invoke(Method.java:498)
	at org.junit.runners.model.FrameworkMethod$1.runReflectiveCall(FrameworkMethod.java:50)
	at org.junit.internal.runners.model.ReflectiveCallable.run(ReflectiveCallable.java:12)
	at org.junit.runners.model.FrameworkMethod.invokeExplosively(FrameworkMethod.java:47)
	at org.junit.internal.runners.statements.InvokeMethod.evaluate(InvokeMethod.java:17)
	at org.junit.runners.ParentRunner.runLeaf(ParentRunner.java:325)
	at org.junit.runners.BlockJUnit4ClassRunner.runChild(BlockJUnit4ClassRunner.java:78)
	at org.junit.runners.BlockJUnit4ClassRunner.runChild(BlockJUnit4ClassRunner.java:57)
	at org.junit.runners.ParentRunner$3.run(ParentRunner.java:290)
	at org.junit.runners.ParentRunner$1.schedule(ParentRunner.java:71)
	at org.junit.runners.ParentRunner.runChildren(ParentRunner.java:288)
	at org.junit.runners.ParentRunner.access$000(ParentRunner.java:58)
	at org.junit.runners.ParentRunner$2.evaluate(ParentRunner.java:268)
	at org.junit.runners.ParentRunner.run(ParentRunner.java:363)
	at org.junit.runner.JUnitCore.run(JUnitCore.java:137)
	at com.intellij.junit4.JUnit4IdeaTestRunner.startRunnerWithArgs(JUnit4IdeaTestRunner.java:68)
	at com.intellij.rt.execution.junit.IdeaTestRunner$Repeater.startRunnerWithArgs(IdeaTestRunner.java:47)
	at com.intellij.rt.execution.junit.JUnitStarter.prepareStreamsAndStart(JUnitStarter.java:242)
	at com.intellij.rt.execution.junit.JUnitStarter.main(JUnitStarter.java:70)

Process finished with exit code 0

我们发现，子方法中的【解析异常】被ParseException的catch抓取，然后抛出ParseException；父方法抓住了这个ParseException；