Java从入门到实战之（29）Java 异常处理之练习

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mb5fca0c87ea3a4 2020-11-10 11:28:00

文章标签 jar flink java apache scala 文章分类 Java 后端开发

1、异常处理的方法

使用 System 类的 System.err.println() 来展示异常的处理方法?

class ExceptionDemo
{
    public static void main(String[] args) {
        try {
            throw new Exception("My Exception");
        } catch (Exception e) {
            System.err.println("Caught Exception");
            System.err.println("getMessage():" + e.getMessage());
            System.err.println("getLocalizedMessage():" + e.getLocalizedMessage());
            System.err.println("toString():" + e);
            System.err.println("printStackTrace():");
            e.printStackTrace();
        }
    }
}

结果：

"C:\Program Files\Java\jdk1.8.0_221\bin\java.exe" "-javaagent:C:\Program Files\JetBrains\IntelliJ IDEA 2019.3.3\lib\idea_rt.jar=60857:C:\Program Files\JetBrains\IntelliJ IDEA 2019.3.3\bin" -Dfile.encoding=UTF-8 -classpath "C:\Program Files\Java\jdk1.8.0_221\jre\lib\charsets.jar;C:\Program Files\Java\jdk1.8.0_221\jre\lib\deploy.jar;C:\Program Files\Java\jdk1.8.0_221\jre\lib\ext\access-bridge-64.jar;C:\Program Files\Java\jdk1.8.0_221\jre\lib\ext\cldrdata.jar;C:\Program Files\Java\jdk1.8.0_221\jre\lib\ext\dnsns.jar;C:\Program Files\Java\jdk1.8.0_221\jre\lib\ext\jaccess.jar;C:\Program Files\Java\jdk1.8.0_221\jre\lib\ext\jfxrt.jar;C:\Program Files\Java\jdk1.8.0_221\jre\lib\ext\localedata.jar;C:\Program Files\Java\jdk1.8.0_221\jre\lib\ext\nashorn.jar;C:\Program Files\Java\jdk1.8.0_221\jre\lib\ext\sunec.jar;C:\Program Files\Java\jdk1.8.0_221\jre\lib\ext\sunjce_provider.jar;C:\Program Files\Java\jdk1.8.0_221\jre\lib\ext\sunmscapi.jar;C:\Program Files\Java\jdk1.8.0_221\jre\lib\ext\sunpkcs11.jar;C:\Program Files\Java\jdk1.8.0_221\jre\lib\ext\zipfs.jar;C:\Program Files\Java\jdk1.8.0_221\jre\lib\javaws.jar;C:\Program Files\Java\jdk1.8.0_221\jre\lib\jce.jar;C:\Program Files\Java\jdk1.8.0_221\jre\lib\jfr.jar;C:\Program Files\Java\jdk1.8.0_221\jre\lib\jfxswt.jar;C:\Program Files\Java\jdk1.8.0_221\jre\lib\jsse.jar;C:\Program Files\Java\jdk1.8.0_221\jre\lib\management-agent.jar;C:\Program Files\Java\jdk1.8.0_221\jre\lib\plugin.jar;C:\Program Files\Java\jdk1.8.0_221\jre\lib\resources.jar;C:\Program Files\Java\jdk1.8.0_221\jre\lib\rt.jar;C:\app\FlinkUdf\target\test-classes;C:\Users\defaultuser0\.m2\repository\junit\junit\4.11\junit-4.11.jar;C:\Users\defaultuser0\.m2\repository\org\hamcrest\hamcrest-core\1.3\hamcrest-core-1.3.jar;C:\Users\defaultuser0\.m2\repository\org\apache\flink\flink-table-api-java-bridge_2.11\1.11.1\flink-table-api-java-bridge_2.11-1.11.1.jar;C:\Users\defaultuser0\.m2\repository\org\apache\flink\flink-table-api-java\1.11.1\flink-table-api-java-1.11.1.jar;C:\Users\defaultuser0\.m2\repository\org\apache\flink\flink-java\1.11.1\flink-java-1.11.1.jar;C:\Users\defaultuser0\.m2\repository\org\apache\commons\commons-lang3\3.3.2\commons-lang3-3.3.2.jar;C:\Users\defaultuser0\.m2\repository\org\apache\commons\commons-math3\3.5\commons-math3-3.5.jar;C:\Users\defaultuser0\.m2\repository\org\apache\flink\flink-streaming-java_2.11\1.11.1\flink-streaming-java_2.11-1.11.1.jar;C:\Users\defaultuser0\.m2\repository\org\apache\flink\flink-runtime_2.11\1.11.1\flink-runtime_2.11-1.11.1.jar;C:\Users\defaultuser0\.m2\repository\org\apache\flink\flink-queryable-state-client-java\1.11.1\flink-queryable-state-client-java-1.11.1.jar;C:\Users\defaultuser0\.m2\repository\org\apache\flink\flink-hadoop-fs\1.11.1\flink-hadoop-fs-1.11.1.jar;C:\Users\defaultuser0\.m2\repository\commons-io\commons-io\2.4\commons-io-2.4.jar;C:\Users\defaultuser0\.m2\repository\org\apache\flink\flink-shaded-netty\4.1.39.Final-11.0\flink-shaded-netty-4.1.39.Final-11.0.jar;C:\Users\defaultuser0\.m2\repository\org\apache\flink\flink-shaded-jackson\2.10.1-11.0\flink-shaded-jackson-2.10.1-11.0.jar;C:\Users\defaultuser0\.m2\repository\org\apache\flink\flink-shaded-zookeeper-3\3.4.14-11.0\flink-shaded-zookeeper-3-3.4.14-11.0.jar;C:\Users\defaultuser0\.m2\repository\commons-cli\commons-cli\1.3.1\commons-cli-1.3.1.jar;C:\Users\defaultuser0\.m2\repository\com\typesafe\akka\akka-actor_2.11\2.5.21\akka-actor_2.11-2.5.21.jar;C:\Users\defaultuser0\.m2\repository\com\typesafe\config\1.3.3\config-1.3.3.jar;C:\Users\defaultuser0\.m2\repository\org\scala-lang\modules\scala-java8-compat_2.11\0.7.0\scala-java8-compat_2.11-0.7.0.jar;C:\Users\defaultuser0\.m2\repository\com\typesafe\akka\akka-stream_2.11\2.5.21\akka-stream_2.11-2.5.21.jar;C:\Users\defaultuser0\.m2\repository\org\reactivestreams\reactive-streams\1.0.2\reactive-streams-1.0.2.jar;C:\Users\defaultuser0\.m2\repository\com\typesafe\ssl-config-core_2.11\0.3.7\ssl-config-core_2.11-0.3.7.jar;C:\Users\defaultuser0\.m2\repository\com\typesafe\akka\akka-protobuf_2.11\2.5.21\akka-protobuf_2.11-2.5.21.jar;C:\Users\defaultuser0\.m2\repository\com\typesafe\akka\akka-slf4j_2.11\2.5.21\akka-slf4j_2.11-2.5.21.jar;C:\Users\defaultuser0\.m2\repository\org\clapper\grizzled-slf4j_2.11\1.3.2\grizzled-slf4j_2.11-1.3.2.jar;C:\Users\defaultuser0\.m2\repository\com\github\scopt\scopt_2.11\3.5.0\scopt_2.11-3.5.0.jar;C:\Users\defaultuser0\.m2\repository\org\xerial\snappy\snappy-java\1.1.4\snappy-java-1.1.4.jar;C:\Users\defaultuser0\.m2\repository\com\twitter\chill_2.11\0.7.6\chill_2.11-0.7.6.jar;C:\Users\defaultuser0\.m2\repository\com\twitter\chill-java\0.7.6\chill-java-0.7.6.jar;C:\Users\defaultuser0\.m2\repository\org\lz4\lz4-java\1.6.0\lz4-java-1.6.0.jar;C:\Users\defaultuser0\.m2\repository\org\apache\flink\flink-shaded-guava\18.0-11.0\flink-shaded-guava-18.0-11.0.jar;C:\Users\defaultuser0\.m2\repository\org\apache\flink\flink-streaming-java_2.11\1.11.1\flink-streaming-java_2.11-1.11.1-tests.jar;C:\Users\defaultuser0\.m2\repository\org\slf4j\slf4j-api\1.7.15\slf4j-api-1.7.15.jar;C:\Users\defaultuser0\.m2\repository\com\google\code\findbugs\jsr305\1.3.9\jsr305-1.3.9.jar;C:\Users\defaultuser0\.m2\repository\org\apache\flink\force-shading\1.11.1\force-shading-1.11.1.jar;C:\Users\defaultuser0\.m2\repository\org\apache\flink\flink-table-planner-blink_2.11\1.11.1\flink-table-planner-blink_2.11-1.11.1.jar;C:\Users\defaultuser0\.m2\repository\org\apache\flink\flink-table-api-scala_2.11\1.11.1\flink-table-api-scala_2.11-1.11.1.jar;C:\Users\defaultuser0\.m2\repository\org\apache\flink\flink-table-api-scala-bridge_2.11\1.11.1\flink-table-api-scala-bridge_2.11-1.11.1.jar;C:\Users\defaultuser0\.m2\repository\org\apache\flink\flink-table-runtime-blink_2.11\1.11.1\flink-table-runtime-blink_2.11-1.11.1.jar;C:\Users\defaultuser0\.m2\repository\org\codehaus\janino\janino\3.0.9\janino-3.0.9.jar;C:\Users\defaultuser0\.m2\repository\org\codehaus\janino\commons-compiler\3.0.9\commons-compiler-3.0.9.jar;C:\Users\defaultuser0\.m2\repository\org\apache\calcite\avatica\avatica-core\1.16.0\avatica-core-1.16.0.jar;C:\Users\defaultuser0\.m2\repository\org\reflections\reflections\0.9.10\reflections-0.9.10.jar;C:\Users\defaultuser0\.m2\repository\org\javassist\javassist\3.19.0-GA\javassist-3.19.0-GA.jar;C:\Users\defaultuser0\.m2\repository\org\apache\flink\flink-streaming-scala_2.11\1.11.1\flink-streaming-scala_2.11-1.11.1.jar;C:\Users\defaultuser0\.m2\repository\org\apache\flink\flink-scala_2.11\1.11.1\flink-scala_2.11-1.11.1.jar;C:\Users\defaultuser0\.m2\repository\org\scala-lang\scala-reflect\2.11.12\scala-reflect-2.11.12.jar;C:\Users\defaultuser0\.m2\repository\org\scala-lang\scala-library\2.11.12\scala-library-2.11.12.jar;C:\Users\defaultuser0\.m2\repository\org\scala-lang\scala-compiler\2.11.12\scala-compiler-2.11.12.jar;C:\Users\defaultuser0\.m2\repository\org\scala-lang\modules\scala-xml_2.11\1.0.5\scala-xml_2.11-1.0.5.jar;C:\Users\defaultuser0\.m2\repository\org\scala-lang\modules\scala-parser-combinators_2.11\1.0.4\scala-parser-combinators_2.11-1.0.4.jar;C:\Users\defaultuser0\.m2\repository\org\apache\flink\flink-table-common\1.11.1\flink-table-common-1.11.1.jar;C:\Users\defaultuser0\.m2\repository\org\apache\flink\flink-core\1.11.1\flink-core-1.11.1.jar;C:\Users\defaultuser0\.m2\repository\org\apache\flink\flink-annotations\1.11.1\flink-annotations-1.11.1.jar;C:\Users\defaultuser0\.m2\repository\org\apache\flink\flink-metrics-core\1.11.1\flink-metrics-core-1.11.1.jar;C:\Users\defaultuser0\.m2\repository\com\esotericsoftware\kryo\kryo\2.24.0\kryo-2.24.0.jar;C:\Users\defaultuser0\.m2\repository\com\esotericsoftware\minlog\minlog\1.2\minlog-1.2.jar;C:\Users\defaultuser0\.m2\repository\org\objenesis\objenesis\2.1\objenesis-2.1.jar;C:\Users\defaultuser0\.m2\repository\org\apache\commons\commons-compress\1.20\commons-compress-1.20.jar;C:\Users\defaultuser0\.m2\repository\org\apache\flink\flink-shaded-asm-7\7.1-11.0\flink-shaded-asm-7-7.1-11.0.jar;C:\Users\defaultuser0\.m2\repository\com\alibaba\fastjson\1.2.73\fastjson-1.2.73.jar;C:\Users\defaultuser0\.m2\repository\org\slf4j\slf4j-log4j12\1.7.7\slf4j-log4j12-1.7.7.jar;C:\Users\defaultuser0\.m2\repository\log4j\log4j\1.2.17\log4j-1.2.17.jar;C:\Users\defaultuser0\.m2\repository\net\sf\json-lib\json-lib\2.4\json-lib-2.4-jdk15.jar;C:\Users\defaultuser0\.m2\repository\commons-beanutils\commons-beanutils\1.8.0\commons-beanutils-1.8.0.jar;C:\Users\defaultuser0\.m2\repository\commons-collections\commons-collections\3.2.1\commons-collections-3.2.1.jar;C:\Users\defaultuser0\.m2\repository\commons-lang\commons-lang\2.5\commons-lang-2.5.jar;C:\Users\defaultuser0\.m2\repository\commons-logging\commons-logging\1.1.1\commons-logging-1.1.1.jar;C:\Users\defaultuser0\.m2\repository\net\sf\ezmorph\ezmorph\1.0.6\ezmorph-1.0.6.jar;C:\Users\defaultuser0\.m2\repository\org\json\json\20180813\json-20180813.jar" Practice.Test1
Caught Exception
getMessage():My Exception
getLocalizedMessage():My Exception
toString():java.lang.Exception: My Exception
printStackTrace():
java.lang.Exception: My Exception
    at Practice.Test1.main(Test1.java:11)

Process finished with exit code 0

2、多个异常处理（多个catch)

对异常的处理：

1，声明异常时，建议声明更为具体的异常，这样可以处理的更具体

2,对方声明几个异常，就对应几个catch块，如果多个catch块中的异常出现继承关系，父类异常catch块放在最下面

class Demo  
{  
    int div(int a,int b) throws ArithmeticException,ArrayIndexOutOfBoundsException//在功能上通过throws的关键字声明该功能可能出现问题  
    {  
        int []arr = new int [a];  
  
        System.out.println(arr[4]);//制造的第一处异常  
  
        return a/b;//制造的第二处异常  
    }  
}  
  
  
class ExceptionDemo  
{  
    public static void main(String[]args) //throws Exception  
    {  
        Demo d = new Demo();  
  
        try  
            {  
                int x = d.div(4,0);//程序运行截图中的三组示例 分别对应此处的三行代码  
                //int x = d.div(5,0);  
                //int x = d.div(4,1);  
                System.out.println("x="+x);   
        }  
        catch (ArithmeticException e)  
        {  
            System.out.println(e.toString());  
        }  
        catch (ArrayIndexOutOfBoundsException e)  
        {  
            System.out.println(e.toString());  
        }  
        catch (Exception e)//父类 写在此处是为了捕捉其他没预料到的异常 只能写在子类异常的代码后面  
                            //不过一般情况下是不写的   
        {  
            System.out.println(e.toString());  
        }  
          
  
  
        System.out.println("Over");  
    }  
  
}

结果：

java.lang.ArrayIndexOutOfBoundsException: 4
Over

3、Finally的用法

Java 中的 Finally 关键一般与try一起使用，在程序进入try块之后，无论程序是因为异常而中止或其它方式返回终止的，finally块的内容一定会被执行。

以下实例演示了如何使用 finally 通过 e.getMessage() 来捕获异常（非法参数异常）？

public class ExceptionDemo2 {
   public static void main(String[] argv) {
      new ExceptionDemo2().doTheWork();
   }
   public void doTheWork() {
      Object o = null;
      for (int i=0; i<5; i++) {
         try {
            o = makeObj(i);
         }
         catch (IllegalArgumentException e) {
            System.err.println
            ("Error: ("+ e.getMessage()+").");
            return;   
         }
         finally {
            System.err.println("都已执行完毕");
            if (o==null)
            System.exit(0);
        }
        System.out.println(o); 
      }
   }
   public Object makeObj(int type) 
   throws IllegalArgumentException {
      if (type == 1)  
      throw new IllegalArgumentException
      ("不是指定的类型： " + type);
      return new Object();
   }
}

结果：

都已执行完毕
java.lang.Object@7852e922
Error: (不是指定的类型：1).
都已执行完毕

4、使用catch处理异常

使用 catch 来处理异常的方法？

public class Main {
    public static void main (String args[]) {
        int array[]={20,20,40};
        int num1=15,num2=10;
        int result=10;
        try{
            result = num1/num2;
            System.out.println("结果为 " +result);
            for(int i =5;i >=0; i--) {
                System.out.println ("数组的元素值为 " +array[i]);
            }
        }
        catch (Exception e) {
            System.out.println("触发异常 : "+e);
        }
    }
}

结果：

结果为 1
触发异常 : java.lang.ArrayIndexOutOfBoundsException: 5

5、多线程异常处理

package Practice;
/**
 * @program: FlinkUdf
 * @description: 文件目录
 * @author: BigData
 * @create: 2020-11-09 14:19
 **/
class  MyThread extends Thread
{
    @Override
    public void run() {
        System.out.println("Throwing in " +"MyThread");
        throw new RuntimeException();
    }
}
public class Test1 {
    public static void main(String[] args) {
        MyThread t=new MyThread();
        t.start();
        try {
            Thread.sleep(1000);
        }
        catch (Exception x)
        {
            System.out.println("Caught it" + x);
        }
    }
}

结果：

"C:\Program Files\Java\jdk1.8.0_221\bin\java.exe" "-javaagent:C:\Program Files\JetBrains\IntelliJ IDEA 2019.3.3\lib\idea_rt.jar=61117:C:\Program Files\JetBrains\IntelliJ IDEA 2019.3.3\bin" -Dfile.encoding=UTF-8 -classpath "C:\Program Files\Java\jdk1.8.0_221\jre\lib\charsets.jar;C:\Program Files\Java\jdk1.8.0_221\jre\lib\deploy.jar;C:\Program Files\Java\jdk1.8.0_221\jre\lib\ext\access-bridge-64.jar;C:\Program Files\Java\jdk1.8.0_221\jre\lib\ext\cldrdata.jar;C:\Program Files\Java\jdk1.8.0_221\jre\lib\ext\dnsns.jar;C:\Program Files\Java\jdk1.8.0_221\jre\lib\ext\jaccess.jar;C:\Program Files\Java\jdk1.8.0_221\jre\lib\ext\jfxrt.jar;C:\Program Files\Java\jdk1.8.0_221\jre\lib\ext\localedata.jar;C:\Program Files\Java\jdk1.8.0_221\jre\lib\ext\nashorn.jar;C:\Program Files\Java\jdk1.8.0_221\jre\lib\ext\sunec.jar;C:\Program Files\Java\jdk1.8.0_221\jre\lib\ext\sunjce_provider.jar;C:\Program Files\Java\jdk1.8.0_221\jre\lib\ext\sunmscapi.jar;C:\Program Files\Java\jdk1.8.0_221\jre\lib\ext\sunpkcs11.jar;C:\Program Files\Java\jdk1.8.0_221\jre\lib\ext\zipfs.jar;C:\Program Files\Java\jdk1.8.0_221\jre\lib\javaws.jar;C:\Program Files\Java\jdk1.8.0_221\jre\lib\jce.jar;C:\Program Files\Java\jdk1.8.0_221\jre\lib\jfr.jar;C:\Program Files\Java\jdk1.8.0_221\jre\lib\jfxswt.jar;C:\Program Files\Java\jdk1.8.0_221\jre\lib\jsse.jar;C:\Program Files\Java\jdk1.8.0_221\jre\lib\management-agent.jar;C:\Program Files\Java\jdk1.8.0_221\jre\lib\plugin.jar;C:\Program Files\Java\jdk1.8.0_221\jre\lib\resources.jar;C:\Program 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Practice.Test1
Exception in thread "Thread-0" java.lang.RuntimeException
    at Practice.MyThread.run(Test1.java:13)
Throwing in MyThread

Process finished with exit code 0

6、获取异常的堆栈信息

如何使用异常类的 printStack() 方法来获取堆栈信息？

public class Main{
    public static void main (String args[]){
        int array[]={20,20,40};
        int num1=15,num2=10;
        int result=10;
        try{
            result = num1/num2;
            System.out.println("The result is" +result);
            for(int i =5; i>=0; i--) {
                System.out.println("The value of array is" +array[i]);
            }
        }
        catch (Exception e) {
            e.printStackTrace();
        }
    }
}

结果：

The result is1
java.lang.ArrayIndexOutOfBoundsException: 5
        at testapp.Main.main(Main.java:28)

7、重载方法异常处理

public class Main {
    double method(int i) throws Exception{
        return i/0;
    }
    boolean method(boolean b) {
        return !b;
    }
    static double method(int x, double y) throws Exception  {
        return x + y ;
    }
    static double method(double x, double y) {
        return x + y - 3;
    }   
    public static void main(String[] args) {
        Main mn = new Main();
        try{
            System.out.println(method(10, 20.0));
            System.out.println(method(10.0, 20));
            System.out.println(method(10.0, 20.0));
            System.out.println(mn.method(10));
        }
        catch (Exception ex){
            System.out.println("exception occoure: "+ ex);
        }
    }
}

结果：

30.0
27.0
27.0
exception occoure: java.lang.ArithmeticException: / by zero

8、链式异常

public class Main {
    public static void main (String args[])throws Exception  {
        int n=20,result=0;
        try{
            result=n/0;
            System.out.println("结果为"+result);
        }
        catch(ArithmeticException ex){
            System.out.println("发算术异常: "+ex);
            try {
                throw new NumberFormatException();
            }
            catch(NumberFormatException ex1) {
                System.out.println("手动抛出链试异常 : "+ex1);
            }
        }
    }
}

结果：

发算术异常: java.lang.ArithmeticException: / by zero
手动抛出链试异常 : java.lang.NumberFormatException

9、自定义异常

通过继承 Exception 来实现自定义异常？

class WrongInputException extends Exception {  // 自定义的类
    WrongInputException(String s) {
        super(s);
    }
}
class Input {
    void method() throws WrongInputException {
        throw new WrongInputException("Wrong input"); // 抛出自定义的类
    }
}
class TestInput {
    public static void main(String[] args){
        try {
            new Input().method();
        }
        catch(WrongInputException wie) {
            System.out.println(wie.getMessage());
        }
    } 
}