（022）Spring Boot之异常处理的两种方式

　　第一种方式，实现ErrorPageRegistrar接口，指定异常状态码或者异常类和对应的跳转页面，如下：

　　pom.xml

<?xml version="1.0" encoding="UTF-8"?>

<project xmlns="http://maven.apache.org/POM/4.0.0" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
    xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd">
    <modelVersion>4.0.0</modelVersion>

    <groupId>com.edu.spring</groupId>
    <artifactId>springboot_web</artifactId>
    <version>1.0.0</version>

    <name>springboot_web</name>
    <!-- FIXME change it to the project's website -->
    <url>http://www.example.com</url>
    <parent> 
        <groupId>org.springframework.boot</groupId> 
        <artifactId>spring-boot-starter-parent</artifactId> 
        <version>2.0.4.RELEASE</version> 
    </parent>
    <properties>
        <project.build.sourceEncoding>UTF-8</project.build.sourceEncoding>
        <maven.compiler.source>1.8</maven.compiler.source>
        <maven.compiler.target>1.8</maven.compiler.target>
    </properties>

    <dependencies>
        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter-web</artifactId>
        </dependency>
    </dependencies>

</project>

　　CommonErrorPageRegistrar.java，实现ErrorPageRegistrar接口，并且装配到spring容器中

package com.edu.spring.springboot;

import org.springframework.boot.web.server.ErrorPage;
import org.springframework.boot.web.server.ErrorPageRegistrar;
import org.springframework.boot.web.server.ErrorPageRegistry;
import org.springframework.http.HttpStatus;
import org.springframework.stereotype.Component;

@Component
public class CommonErrorPageRegistrar implements ErrorPageRegistrar{

    @Override
    public void registerErrorPages(ErrorPageRegistry registry) {
        
        ErrorPage e404=new ErrorPage(HttpStatus.NOT_FOUND,"/404.html");
        ErrorPage e500=new ErrorPage(HttpStatus.INTERNAL_SERVER_ERROR,"/500.html");
        ErrorPage args=new ErrorPage(IllegalArgumentException.class,"/args.html");
        ErrorPage nullpoint=new ErrorPage(NullPointerException.class,"/nullpoint.html");

        registry.addErrorPages(e404,e500,args,nullpoint);
    }

    
}

　　异常跳转页面如下：

 　　UserController.java测试类

package com.edu.spring.springboot;

import org.springframework.web.bind.annotation.RequestMapping;
import org.springframework.web.bind.annotation.RestController;

@RestController
public class UserController {
    
    @RequestMapping("/user/innererror")
    public String innererror(){
        System.out.println("============innererror=============");
        int a=10/0;
        return "innererror" +a;
    }

    @RequestMapping("/user/index")
    public String index(){
        System.out.println("============index=============");
        throw new IllegalArgumentException("IllegalArgumentException抛出的异常");
    }
    
    @RequestMapping("/user/empty")
    public String empty(){
        System.out.println("============empty=============");
        throw new NullPointerException("NullPointerException抛出的异常");
    }
}

　　App.java，排除掉默认的处理类：ErrorMvcAutoConfiguration（高版本不用排除，本示例可以不排除）

package com.edu.spring.springboot;

import org.springframework.boot.SpringApplication;
import org.springframework.boot.autoconfigure.SpringBootApplication;
import org.springframework.boot.autoconfigure.web.servlet.error.ErrorMvcAutoConfiguration;

@SpringBootApplication(exclude=ErrorMvcAutoConfiguration.class)
public class App 
{
    public static void main(String[] args) {
         SpringApplication.run(App.class, args);
    }
}

　　浏览器输入：http://localhost:8080/user/aaa ，该url不存在，跳转404页面，如下：

 　　浏览器输入：http://localhost:8080/user/innererror ，跳转500页面，如下：

 　　浏览器输入：http://localhost:8080/user/index ，跳转args页面，如下：

 　　浏览器输入：http://localhost:8080/user/empty ，跳转空指针页面，如下：

 　　假如程序抛出的异常满足多个匹配，到底匹配会匹配哪个，尚未看源码。

　　第二种方式，使用@ControllerAdvice、@ExceptionHandler注解，如下

　　BookController.java

package com.edu.spring.springboot;

import java.io.FileNotFoundException;

import org.springframework.web.bind.annotation.ExceptionHandler;
import org.springframework.web.bind.annotation.RequestMapping;
import org.springframework.web.bind.annotation.RestController;

@RestController
public class BookController {

    @ExceptionHandler(value=Exception.class)
    public String error(Exception e){
        return "found exception:"+e.getMessage();
    }
    
    @RequestMapping("/book/error1")
    public String error1 () throws FileNotFoundException{
        throw new FileNotFoundException(" book.txt not found");
    }
    
    @RequestMapping("/book/error2")
    public String error2 () throws ClassNotFoundException{
        throw new ClassNotFoundException(" Book class not found");
    }
}

　　UserController.java

package com.edu.spring.springboot;

import org.springframework.web.bind.annotation.RequestMapping;
import org.springframework.web.bind.annotation.RestController;

@RestController
public class UserController {

    @RequestMapping("/user/index")
    public String index(){
        System.out.println("============index=============");
        throw new IllegalArgumentException("IllegalArgumentException抛出的异常");
    }
}

　　GlobalExceptionHandler.java

package com.edu.spring.springboot;

import org.springframework.web.bind.annotation.ControllerAdvice;
import org.springframework.web.bind.annotation.ExceptionHandler;
import org.springframework.web.bind.annotation.ResponseBody;

@ControllerAdvice
public class GlobalExceptionHandler {

    @ExceptionHandler(value=Exception.class)
    @ResponseBody
    public String error(Exception e){
        return "global exception:"+e.getClass().getName();
    }
}

　　App.java

package com.edu.spring.springboot;

import org.springframework.boot.SpringApplication;
import org.springframework.boot.autoconfigure.SpringBootApplication;

@SpringBootApplication
public class App 
{
    public static void main(String[] args) {
         SpringApplication.run(App.class, args);
    }
}

　　浏览器输入：http://localhost:8080/book/error1 ，被方法所在类中的@ExceptionHandler注解捕获，如下：

 　　浏览器输入：http://localhost:8080/book/error2 ，被方法所在类中的@ExceptionHandler注解捕获，如下：

 　　浏览器输入：http://localhost:8080/user/index ，被全局异常类GlobalExceptionHandler中的@ExceptionHandler注解捕获，如下：

 　　说明：程序抛出的异常优先在本类中处理，如果本类中没有处理的方法，则全局异常会处理