JSON和全局处理异常

目录

一、SpringMVC对JSON的支持

导入pom依赖

配置springmvc-servlet.xml (配置适配器)

使用@ResponseBody

JOSN的各种场景 

二、SpringMVC 的全局异常处理

为什么要全局异常处理

异常处理思路

SpringMVC异常分类

1）Spring MVC提供的简单异常处理器

2）实现异常处理接口HandlerExceptionResolver

3）使用@ControllerAdvice + @ExceptionHandler

全局异常处理JSON返回 

---

一、SpringMVC对JSON的支持

导入pom依赖

pom.xml

<!-- 用来springmvc支持JSON数据转换-->
        <dependency>
            <groupId>com.fasterxml.jackson.core</groupId>
            <artifactId>jackson-databind</artifactId>
            <version>2.9.3</version>
        </dependency>
        <dependency>
            <groupId>com.fasterxml.jackson.core</groupId>
            <artifactId>jackson-core</artifactId>
            <version>2.9.3</version>
        </dependency>
        <dependency>
            <groupId>com.fasterxml.jackson.core</groupId>
            <artifactId>jackson-annotations</artifactId>
            <version>2.9.3</version>
        </dependency>

配置springmvc-servlet.xml (配置适配器)

springmvc-servlet.xml

<!--  支持JSON数据 返回的适配器 -->
<bean class="org.springframework.web.servlet.mvc.method.annotation.RequestMappingHandlerAdapter">
        <property name="messageConverters">
            <list>
                <ref bean="mappingJackson2HttpMessageConverter"/>
            </list>
        </property>
    </bean>
    <bean id="mappingJackson2HttpMessageConverter"
          class="org.springframework.http.converter.json.MappingJackson2HttpMessageConverter">
        <!--处理中文乱码以及避免IE执行AJAX时，返回JSON出现下载文件-->
        <property name="supportedMediaTypes">
            <list>
                <value>text/html;charset=UTF-8</value>
                <value>text/json;charset=UTF-8</value>
                <value>application/json;charset=UTF-8</value>
            </list>
        </property>
</bean>

使用@ResponseBody

凡是需要返回JSON数据的都要使用@responseBody

JsonController.java

package com.maomao.ssm.controller;

import org.springframework.stereotype.Controller;
import org.springframework.web.bind.annotation.RequestMapping;
import org.springframework.web.bind.annotation.ResponseBody;

@Controller
@RequestMapping("/clz/json")
public class JsonController {

    @ResponseBody
    @RequestMapping("/clzEdit")
    public String list(){
        System.out.println("JsonController.clzEdit");
        return "clzEdit";
    }
}

使用@ResponseBody后返回的不再是界面，而是直接返回 字符串

在地址栏输入：localhost:8080/clz/json/clzEdit运行后得到的就是字符串

 

JOSN的各种场景 

后台代码

ClazzMapper.xml

<select id="listMapPager" parameterType="java.util.Map" resultType="java.util.Map">
    select
    <include refid="Base_Column_List" />
    from t_struts_class
    <where>
      <if test="cname !=null and cname!=''">
        and cname like concat('%',#{cname},'%')
      </if>
      <if test="cid !=null and cid!=''">
        and cid =#{cid}
      </if>
    </where>
  </select>

JsonController.java

package com.maomao.ssm.controller;

import com.maomao.ssm.biz.ClazzBiz;
import com.maomao.ssm.model.Clazz;
import com.maomao.ssm.util.PageBean;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.stereotype.Controller;
import org.springframework.web.bind.annotation.RequestMapping;
import org.springframework.web.bind.annotation.ResponseBody;

import javax.servlet.http.HttpServletRequest;
import java.util.HashMap;
import java.util.List;
import java.util.Map;

@RestController
@RequestMapping("/clz/json")
public class JsonController {
    @Autowired
    private ClazzBiz clazzBiz;

    @RequestMapping("/clzEdit")
    public String list(){
        System.out.println("JsonController.clzEdit");
        return "clzEdit";
    }

    
   // 返回List<T>
    @RequestMapping("/list")
    public List<Clazz> list(HttpServletRequest request,Clazz clazz){
        PageBean pageBean=new PageBean();
        pageBean.setRequest(request);
        return this.clazzBiz.listPager(clazz, pageBean);
    }

    // 返回List<Map>
    @RequestMapping("/listMap")
    public List<Map> listMap(HttpServletRequest request,Clazz clazz){
        PageBean pageBean=new PageBean();
        pageBean.setRequest(request);
        return this.clazzBiz.listMapPager(clazz, pageBean);
    }

    //返回Map
    @RequestMapping("/map")
    public Map map(HttpServletRequest request,Clazz clazz){
       PageBean pageBean=new PageBean();
       pageBean.setRequest(request);
       return this.clazzBiz.listMapPager(clazz,pageBean).get(0);
    }

//    返回T
    @RequestMapping("/load")
    public Clazz load(HttpServletRequest request, Clazz clazz){
//        http://localhost:8080/clz/json/load?cid=1
        PageBean pageBean=new PageBean();
        pageBean.setRequest(request);
        return this.clazzBiz.listPager(clazz, pageBean).get(0);
    }

    // 混合混合对象
    @RequestMapping("/hunhe")
    public Map hunhe(HttpServletRequest request, Clazz clazz) {
        PageBean pageBean = new PageBean();
        pageBean.setRequest(request);
        List<Clazz> lst = this.clazzBiz.listPager(clazz, pageBean);
        Map map = new HashMap();
        map.put("data",lst);
        map.put("pageBean",pageBean);
        return map;
    }

}

前台代码

index,jsp

<%--
  Created by IntelliJ IDEA.
  User: Administrator
  Date: 2022/8/22
  Time: 18:20
  To change this template use File | Settings | File Templates.
--%>
<%@ page contentType="text/html;charset=UTF-8" language="java" %>
<html>
<head>
    <title>测试json数据返回</title>
</head>
<body>
<h3>JSON</h3>
<a href="${pageContext.request.contextpath}/clz/json/list">返回List&lt;T&gt;</a><hr>
<a href="${pageContext.request.contextpath}/clz/json/listMap">返回List&lt;Map&gt;</a><hr>
<a href="${pageContext.request.contextpath}/clz/json/load?cid=1">返回T</a><hr>
<a href="${pageContext.request.contextpath}/clz/json/map?cid=1">返回Map</a><hr>
<a href="${pageContext.request.contextpath}/clz/json/hunhe">返回混合</a><hr>
</body>

</html>

运行效果 

 

 

二、SpringMVC 的全局异常处理

为什么要全局异常处理

我们知道，系统中异常包括：编译时异常和运行时异常RuntimeException，前者通过捕获异常从而获取异常信息，后者主要通过规范代码开发、测试通过手段减少运行时异常的发生。在开发中，不管是dao层、service层还是controller层，都有可能抛出异常，在springmvc中，能将所有类型的异常处理从各处理过程解耦出来，既保证了相关处理过程的功能较单一，也实现了异常信息的统一处理和维护。

异常处理思路

系统的dao、service、controller出现异常都通过throws Exception向上抛出，最后由springmvc前端控制器交由异常处理器进行异常处理。springmvc提供全局异常处理器（一个系统只有一个异常处理器）进行统一异常处理。

SpringMVC异常分类

1）Spring MVC提供的简单异常处理器

SimpleMappingExceptionResolver

springmvc-servlet.xml

<!-- springmvc提供的简单异常处理器 -->
    <bean class="org.springframework.web.servlet.handler.SimpleMappingExceptionResolver">
        <!-- 定义默认的异常处理页面 -->
        <property name="defaultErrorView" value="error"/>
        <!-- 定义异常处理页面用来获取异常信息的变量名，也可不定义，默认名为exception -->
        <property name="exceptionAttribute" value="ex"/>
        <!-- 定义需要特殊处理的异常，这是重要点 -->
        <property name="exceptionMappings">
            <props>
                <prop key="java.lang.RuntimeException">error</prop>
            </props>
            <!-- 还可以定义其他的自定义异常 -->
        </property>
    </bean>

 error.jsp 

<%--
  Created by IntelliJ IDEA.
  User: Administrator
  Date: 2022/8/23
  Time: 20:10
  To change this template use File | Settings | File Templates.
--%>
<%@ page contentType="text/html;charset=UTF-8" language="java" %>
<html>
<head>
    <title>错误信息页面</title>
</head>
<body>
${ex}
</body>
</html>

 JsonControler.java

    @RequestMapping("/list")
    public List<Clazz> list(Clazz clazz, HttpServletRequest req){
        PageBean pageBean = new PageBean();
        pageBean.setRequest(req);
        if(true) {
            throw new RuntimeException("查询班级的信息异常，异常处在于JsonController.list方法中");
        }
        List<Clazz> lst = this.clazzBiz.listPager(clazz, pageBean);
        return lst;
    }

ClazzBizImpl.java 

@Override
    public List<Map> MaplistPager(Clazz clazz,PageBean pageBean) {
        if (true)
            throw new RuntimeException("错误出现在 ClazzBizImpl.mapListPager...");
        return clazzMapper.listMapPager(clazz);
    }

 

2）实现异常处理接口HandlerExceptionResolver

自定义自己的异常处理器

先将上面SpringMVC中关于异常处理的配置取消掉

GlobalException.java

package com.maomao.ssm.exception;

public class GlobalException extends RuntimeException {
    public GlobalException() {
    }

    public GlobalException(String message) {
        super(message);
    }

    public GlobalException(String message, Throwable cause) {
        super(message, cause);
    }

    public GlobalException(Throwable cause) {
        super(cause);
    }

    public GlobalException(String message, Throwable cause, boolean enableSuppression, boolean writableStackTrace) {
        super(message, cause, enableSuppression, writableStackTrace);
    }
    
}

  异常处理器 GlobalExceptionHandler

package com.maomao.ssm.exception;

import org.springframework.stereotype.Component;
import org.springframework.web.servlet.HandlerExceptionResolver;
import org.springframework.web.servlet.ModelAndView;

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

@Component
public class GlobalExceptionHandler implements HandlerExceptionResolver {
    @Override
    public ModelAndView resolveException(HttpServletRequest httpServletRequest,
                                         HttpServletResponse httpServletResponse,
                                         Object o, Exception e) {
        ModelAndView mv = new ModelAndView();
        mv.setViewName("error");
        if (e instanceof GlobalException){
            GlobalException globalException = (GlobalException) e;
            mv.addobject("ex",globalException.getMessage());
            mv.addobject("msg","全局异常,错误码501....");
        }else if (e instanceof RuntimeException){
            RuntimeException runtimeException = (RuntimeException) e;
            mv.addobject("ex",runtimeException.getMessage());
            mv.addobject("msg","运行时异常,错误码601....");
        }

        return mv;
    }
}

测试代码controller层

    @RequestMapping("/load")
    public Clazz load(HttpServletRequest req, Clazz clazz){
        if(clazz.getCid() != null){
            List<Clazz> lst = this.clazzBiz.listPager(clazz, null);
            if (true)
                throw new GlobalException("错误出现在 JsonController.load...");
            return lst.get(0);
        }
        return null;
    }

结果

 

3）使用@ControllerAdvice + @ExceptionHandler

package com.cxy.Exception;
 
import org.springframework.web.bind.annotation.ControllerAdvice;
import org.springframework.web.bind.annotation.ExceptionHandler;
import org.springframework.web.servlet.ModelAndView;
 
 
public class GlobalExceptionResovler {
 
    @ExceptionHandler
    public ModelAndView handler(Exception e){
        ModelAndView mv = new ModelAndView();
        mv.setViewName("error");
        if (e instanceof GlobalException){
            GlobalException globalException = (GlobalException) e;
            mv.addobject("ex",globalException.getMessage());
            mv.addobject("msg","全局异常....");
        }else if (e instanceof RuntimeException){
            RuntimeException runtimeException = (RuntimeException) e;
            mv.addobject("ex",runtimeException.getMessage());
            mv.addobject("msg","运行时异常....");
        }
        return mv;
    }
}

 

全局异常处理JSON返回 

package com.maomao.ssm.exception;

import org.springframework.web.bind.annotation.ExceptionHandler;
import org.springframework.web.bind.annotation.RestControllerAdvice;

import java.util.HashMap;
import java.util.Map;

@RestControllerAdvice
public class GlobalExceptionjsonResolver {
    @ExceptionHandler
    public Map handler(Exception e) {
        Map map = new HashMap();
        if (e instanceof GlobalException) {
            GlobalException globalException = (GlobalException) e;
            map.put("ex", globalException.getMessage());
            map.put("msg", "全局异常 GlobalExceptionResolver,错误码501....");
        } else if (e instanceof RuntimeException) {
            RuntimeException runtimeException = (RuntimeException) e;
            map.put("ex", runtimeException.getMessage());
            map.put("msg", "运行时异常 GlobalExceptionResolver,错误码601....");
        }
        return map;
    }
}