springMVC拦截器从Request中获取Json格式并解决request的请求流只能读取一次的问题

背景

在使用SSM（你问我什么叫SSM，我一拳锤爆你的狗头）做开发的时候，经常会使用@RequestBody注解，这个注解是非常的好用。但是如果你想在请求参数传到后台的时候做一个参数检验，当然可以！使用SpringMVC的拦截器，在拦截器里把request的数据读取出来不就行了！！，但是在使用了拦截器的时候会出现一个问题！！！！你在拦截器读取了request的数据，在Controller里面@RequestBody注解获取Json就会失败就读取不到数据！！！！那就是RequestBody是流的形式读取的，流读取一次就没有了！！

为什么使用RequestBody只能读取一遍请求数据流？

那是因为流对应的是数据，数据放在内存中，有的是部分放在内存中。read 一次标记一次当前位置（mark position），第二次read就从标记位置继续读（从内存中copy）数据。 所以这就是为什么读了一次第二次是空了。 怎么让它不为空呢？只要inputstream 中的pos 变成0就可以重写读取当前内存中的数据。javaAPI中有一个方法public void reset() 这个方法就是可以重置pos为起始位置，但是不是所有的IO读取流都可以调用该方法！ServletInputStream是不能调用reset方法，这就导致了只能调用一次getInputStream()。

解决办法：重写HttpServletRequestWrapper方法

这种方法就是通过重写HttpServletRequestWrapper把request的保存下来，然后通过过滤器保存下来的request在填充进去，这样就可以多次读取request了

1.重写HttpServletRequestWrapper方法

public class RequestWrapper extends HttpServletRequestWrapper {     private final String body;     public RequestWrapper(HttpServletRequest request) throws IOException {         super(request);         StringBuilder stringBuilder = new StringBuilder();         BufferedReader bufferedReader = null;         try {             InputStream inputStream = request.getInputStream();             if (inputStream != null) {                 bufferedReader = new BufferedReader(new InputStreamReader(inputStream));                 char[] charBuffer = new char[128];                 int bytesRead = -1;                 while ((bytesRead = bufferedReader.read(charBuffer)) > 0) {                     stringBuilder.append(charBuffer, 0, bytesRead);                 }             } else {                 stringBuilder.append("");             }         } catch (IOException ex) {             throw ex;         } finally {             if (bufferedReader != null) {                 try {                     bufferedReader.close();                 } catch (IOException ex) {                     throw ex;                 }             }         }         body = stringBuilder.toString();     }      @Override     public ServletInputStream getInputStream() throws IOException {         final ByteArrayInputStream byteArrayInputStream = new ByteArrayInputStream(body.getBytes());         ServletInputStream servletInputStream = new ServletInputStream() {             public boolean isFinished() {                 return false;             }             public boolean isReady() {                 return false;             }             public void setReadListener(ReadListener readListener) {}             public int read() throws IOException {                 return byteArrayInputStream.read();             }         };         return servletInputStream;      }     @Override     public BufferedReader getReader() throws IOException {         return new BufferedReader(new InputStreamReader(this.getInputStream()));     }     public String getBody() {         return this.body;     }  }

2.拦截器CommonInterceptor

public class CommonInterceptor extends HandlerInterceptorAdapter {     private final Log log = LogFactory.getLog(CommonInterceptor.class);     public CommonInterceptor() {     }     public boolean preHandle(HttpServletRequest request, HttpServletResponse response, Object handler) throws Exception {         RequestWrapper myRequestWrapper = new RequestWrapper((HttpServletRequest) request);         String body = myRequestWrapper.getBody();         System.out.println("我是拦截器："+body);         // do something         return true;      }     public void postHandle(HttpServletRequest request, HttpServletResponse response, Object handler, ModelAndView modelAndView) throws Exception {         super.postHandle(request, response, handler, modelAndView);     }     public void afterCompletion(HttpServletRequest request, HttpServletResponse response, Object handler, Exception ex) throws Exception {         super.afterCompletion(request, response, handler, ex);     }     public void afterConcurrentHandlingStarted(HttpServletRequest request, HttpServletResponse response, Object handler) throws Exception {         super.afterConcurrentHandlingStarted(request, response, handler);     } }

3.在spring-mvc.xml声明springMVC的拦截器

<mvc:interceptors>     <mvc:interceptor>         <mvc:mapping path="/**"/>         <bean class="com.sdut.platform.core.CommonInterceptor"/>     </mvc:interceptor> </mvc:interceptors>

4.过滤器HttpServletFilter类

public class HttpServletFilter implements Filter {      public void init(FilterConfig filterConfig) throws ServletException {     }     public void doFilter(ServletRequest request, ServletResponse response, FilterChain chain) throws IOException, ServletException {         ServletRequest requestWrapper = null;         System.out.println("我是过滤器");         if(request instanceof HttpServletRequest) {             requestWrapper = new RequestWrapper((HttpServletRequest) request);         }         if(requestWrapper == null) {             chain.doFilter(request, response);         } else {             chain.doFilter(requestWrapper, response);         }     }     public void destroy() {      } }

5.在web.xml中注册过滤器

<filter>     <filter-name>requestFilter</filter-name>     <filter-class>com.sdut.platform.core.HttpServletFilter</filter-class> </filter> <filter-mapping>     <filter-name>requestFilter</filter-name>     <url-pattern>/*</url-pattern> </filter-mapping>

经过测试完全可以并且不出现其他错误。

解决办法：AOP切面获取request(一般做日志管理会经常使用这种办法)

这个办法我还没做测试

HttpServletRequest request = ((ServletRequestAttributes) RequestContextHolder.currentRequestAttributes()).getRequest(); HttpServletResponse response = ((ServletRequestAttributes) RequestContextHolder.currentRequestAttributes()).getResponse();