Spring MVC annotation (二)

@ExceptionHandler

Spring注解，改变了我的开发思路。前段时间，用@RequestBody，@ResponseBody，不费吹灰之力就解决了JSon自动绑定。接着就发现，如果遇到RuntimeException，需要给出一个默认返回JSON。 

以前都是用SimpleMappingExceptionResolver拦截实现，今天偶尔看下资料，@ExceptionHandler，就把这个异常给拦截了，太方便了！ 

直接上代码： 

1. @Controller  
2. public class AccessController {  
3.   
4.     /** 
5.      * 异常页面控制 
6.      *  
7.      * @param runtimeException 
8.      * @return 
9.      */  
10.     @ExceptionHandler(RuntimeException.class)  
11.     public @ResponseBody  
12.     Map<String,Object> runtimeExceptionHandler(RuntimeException runtimeException) {  
13.         logger.error(runtimeException.getLocalizedMessage());  
14.   
15.         Map model = new TreeMap();  
16.         model.put("status", false);  
17.         return model;  
18.     }  
19.   
20. }  

当这个Controller中任何一个方法发生异常，一定会被这个方法拦截到。然后，输出日志。封装Map并返回，页面上得到status为false。就这么简单。
或者这个有些有些复杂，来个简单易懂的，上代码： 

1. @Controller  
2. public class AccessController {  
3.     /** 
4.      * 异常页面控制 
5.      *  
6.      * @param runtimeException 
7.      * @return 
8.      */  
9.     @ExceptionHandler(RuntimeException.class)  
10.     public String runtimeExceptionHandler(RuntimeException runtimeException,  
11.             ModelMap modelMap) {  
12.         logger.error(runtimeException.getLocalizedMessage());  
13.   
14.         modelMap.put("status", IntegralConstant.FAIL_STATUS);  
15.         return "exception";  
16.     }  
17. }  

================================================================

（http://www.mkyong.com/spring-mvc/spring-mvc-exceptionhandler-example/）

In this tutorial, we show you how to do exception handling in Spring MVC frameworks. Normally, we use@ExceptionHandler to decide which “view” should be returned back if certain exception is raised.

P.S This @ExceptionHandler class is available since Spring 3.0

1. Project Structure

Review the project directory structure, a standard Maven project.

2. Custom Exception

A custom exception, with custom error code and error description.

public class CustomGenericException extends RuntimeException {private static final long serialVersionUID = 1L;private String errCode;private String errMsg;public String getErrCode() {return errCode;}public void setErrCode(String errCode) {this.errCode = errCode;}public String getErrMsg() {return errMsg;}public void setErrMsg(String errMsg) {this.errMsg = errMsg;}public CustomGenericException(String errCode, String errMsg) {this.errCode = errCode;this.errMsg = errMsg;}}

3. Spring Controller

A Spring controller, review the execution-flows below :

1. If user provide a /error request, it throws “CustomGenericException”, and the handleCustomException() method will be fired.
2. If user provide a /io-error request, it throws “IOException”, and the handleAllException() method will be fired.

import java.io.IOException;import org.springframework.stereotype.Controller;import org.springframework.web.bind.annotation.ExceptionHandler;import org.springframework.web.bind.annotation.PathVariable;import org.springframework.web.bind.annotation.RequestMapping;import org.springframework.web.bind.annotation.RequestMethod;import org.springframework.web.servlet.ModelAndView;import com.mkyong.web.exception.CustomGenericException;@Controllerpublic class MainController {@RequestMapping(value = "/{type:.+}", method = RequestMethod.GET)public ModelAndView getPages(@PathVariable("type") String type)throws Exception {  if ("error".equals(type)) {// go handleCustomExceptionthrow new CustomGenericException("E888", "This is custom message");  } else if ("io-error".equals(type)) {// go handleAllExceptionthrow new IOException();  } else {return new ModelAndView("index").addObject("msg", type);  }}@ExceptionHandler(CustomGenericException.class)public ModelAndView handleCustomException(CustomGenericException ex) {ModelAndView model = new ModelAndView("error/generic_error");model.addObject("errCode", ex.getErrCode());model.addObject("errMsg", ex.getErrMsg());return model;}@ExceptionHandler(Exception.class)public ModelAndView handleAllException(Exception ex) {ModelAndView model = new ModelAndView("error/generic_error");model.addObject("errMsg", "this is Exception.class");return model;}}

4. JSP Pages

pages/index.jsp

<%@taglib prefix="c" uri="http://java.sun.com/jsp/jstl/core"%><html><body><h2>Spring MVC @ExceptionHandler Example</h2><c:if test="${not empty msg}"><h2>${msg}</h2></c:if></body></html>

pages/error/generic_error.jsp

<%@taglib prefix="c" uri="http://java.sun.com/jsp/jstl/core"%><html><body><c:if test="${not empty errCode}"><h1>${errCode} : System Errors</h1></c:if><c:if test="${empty errCode}"><h1>System Errors</h1></c:if><c:if test="${not empty errMsg}"><h2>${errMsg}</h2></c:if></body></html>

5. Testing

Review following 3 test cases :

1. http://localhost:8080/SpringMvcExample/anything

2. http://localhost:8080/SpringMvcExample/error

3. http://localhost:8080/SpringMvcExample/io-error

6. @ControllerAdvice Example

The above @ExceptionHandler example is only apply to a single controller, to apply it globally (all controllers), annotate a class with @ControllerAdvice.

import org.springframework.web.bind.annotation.ControllerAdvice;import org.springframework.web.bind.annotation.ExceptionHandler;import org.springframework.web.servlet.ModelAndView;import com.mkyong.web.exception.CustomGenericException;@ControllerAdvicepublic class GlobalExceptionController {@ExceptionHandler(CustomGenericException.class)public ModelAndView handleCustomException(CustomGenericException ex) {ModelAndView model = new ModelAndView("error/generic_error");model.addObject("errCode", ex.getErrCode());model.addObject("errMsg", ex.getErrMsg());return model;}@ExceptionHandler(Exception.class)public ModelAndView handleAllException(Exception ex) {ModelAndView model = new ModelAndView("error/generic_error");model.addObject("errMsg", "this is Exception.class");return model;}}