014-Spring Boot web【三】拦截器HandlerInterceptor、异常处理页面，全局异常处理ControllerAdvice

一、拦截器HandlerInterceptor

1.1、HandlerInterceptor接口说明

　　preHandle，congtroller执行前，如果返回false请求终端

　　postHandle，controller执行之后，页面渲染前

　　afterCompletion，整个请求结束后，页面也渲染完毕，一般是资源清理操作

　　同时提供异步拦截器AsyncHandlerInterceptor

1.2、拦截器使用步骤

　　1》写一个拦截器，实现HandlerInterceptor 接口

　　2》写一个类，继承WebMvcConfigurerAdapter抽象类，然后重写addInterceptors方法，把上一步的拦截器加入registry.addInterceptor(new LogHandlerInterceptor());

1.3、示例

　　启动类

package com.lhx.spring.springboot_web;

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

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

　　建立UserController

package com.lhx.spring.springboot_web;

import org.springframework.stereotype.Controller;
import org.springframework.web.bind.annotation.GetMapping;

@Controller
public class UserController {

    @GetMapping(value = "/user/home")
    public String home() {
        System.out.println("--------user home--------");
        return "user home";
    }    
}

　　增加拦截器LogHandlerInterceptor 

package com.lhx.spring.springboot_web;

import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;

import org.springframework.web.servlet.HandlerInterceptor;
import org.springframework.web.servlet.ModelAndView;

public class LogHandlerInterceptor implements HandlerInterceptor {

    @Override
    public boolean preHandle(HttpServletRequest request, HttpServletResponse response, Object handler)
            throws Exception {
        System.out.println("----------preHandle----------"+handler.getClass());
        
        
        return true;
    }

    @Override
    public void postHandle(HttpServletRequest request, HttpServletResponse response, Object handler,
            ModelAndView modelAndView) throws Exception {
        System.out.println("----------postHandle----------");

    }

    @Override
    public void afterCompletion(HttpServletRequest request, HttpServletResponse response, Object handler, Exception ex)
            throws Exception {
        System.out.println("----------afterCompletion----------");

    }

}

　　增加配置类WebConfiguration 

package com.lhx.spring.springboot_web;

import org.springframework.boot.SpringBootConfiguration;
import org.springframework.context.annotation.Configuration;
import org.springframework.web.servlet.config.annotation.InterceptorRegistry;
import org.springframework.web.servlet.config.annotation.WebMvcConfigurerAdapter;

@SpringBootConfiguration
public class WebConfiguration extends WebMvcConfigurerAdapter {

    @Override
    public void addInterceptors(InterceptorRegistry registry) {
        registry.addInterceptor(new LogHandlerInterceptor());
    }

}

二、异常处理

2.1、编码抛出异常代码

    @GetMapping(value = "/user/help")
    @ResponseBody
    public String help() {
        throw new IllegalArgumentException("args is empty");
    }    

2.2、分析代码

　　查看：org.springframework.boot.autoconfigure.web.ErrorMvcAutoConfiguration，发现默认已经被springboot定制。

　　去除springboot默认异常显示，只需在启动类添加：@SpringBootApplication(exclude=ErrorMvcAutoConfiguration.class)即可。则返回错误就会变成Tomcat提供的

2.3、添加自定义错误页

　　1》去除springboot默认的：@SpringBootApplication(exclude=ErrorMvcAutoConfiguration.class)

　　2》在src/main/resources下增加public，在pulic中增加404.html，500.html

　　3》增加CommonErrorPageRegistry实现ErrorPageRegistrar增加@Component注解，可以针对错误码处理或者具体异常处理

package com.lhx.spring.springboot_web;

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

@Component
public class CommonErrorPageRegistry 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");
        registry.addErrorPages(e404);
        registry.addErrorPages(e500);
        registry.addErrorPages(args);
    }

}

　　　　以上将404,500逻辑添加

 三、全局异常处理

3.1、局部异常处理

　　当前Controller使用，可以在当前Controller中使用ExceptionHandler注解

如下代码

package com.lhx.spring.springboot_web;

import java.io.FileNotFoundException;

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

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

　　其中：@ExceptionHandler(value = Exception.class) 代表所有；也可指代具体异常，如文件没有发现@ExceptionHandler(value = FileNotException.class)

3.2、全局异常处理

　　1》写一个GlobalExceptionHandler异常处理类，并且使用@ControllerAdvice注解

　　2》写一个方法，需要添加@ExceptionHandler(value = Exception.class)注解，在方法中编写具体代码逻辑

package com.lhx.spring.springboot_web;

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 errorHandler(Exception e) {
        return "global error:" + e.getClass().getName();
    }
}

　　可以有多个不同的异常处理。

3.3、就近原则

　　局部异常优先级高于全局异常处理

一个比较通用的写法

@ControllerAdvice
@ResponseBody
public class ResponseExceptionHandler {
    Logger logger=LoggerFactory.getLogger(ResponseExceptionHandler.class);

    @ExceptionHandler(ResponseException.class)
    public ResponseEntity<ResponseResult> handleException(Exception e) {
        logger.error("请求异常信息",e);
        ResponseException cex = (ResponseException) e;
        return new ResponseEntity(ResponseResult.error(cex.getResponseCode()), HttpStatus.OK);
    }

}