修改Request 中的數據

攔截器修改參數

今天一位網友開發中遇到一個需求，他需要在Request中修改傳遞過來的數據。開始的時候他在攔截器中修改，在攔截器中可以獲取到從前台request中
傳遞過來的數據。他寫法大致如下：自定義攔截器繼承HandlerInterceptorAdapter

    @Override
    public boolean preHandle(HttpServletRequest request,
            HttpServletResponse response, Object handler) throws Exception {
        //在這里request中獲取參數並修改。
        return true;
    }
 
    @Override
    public void postHandle(HttpServletRequest request,
            HttpServletResponse response, Object handler,
            ModelAndView modelAndView) throws Exception {
       
    }
 
    @Override
    public void afterCompletion(HttpServletRequest request,
            HttpServletResponse response, Object handler, Exception ex)
            throws Exception {
      
    }

不過在controller 中獲取在攔截器中修改的參數，發現參數還是以前老的數據，也就是說在攔截器中修改request中出傳遞過來的數據並沒有生效。
數據沒有生效 參考

於是我看了 HttpServletRequestWrapper 源碼，在Filter中測試了，發現可以成功修改傳遞過來的參數

public class HTMLFilter implements Filter {

	public void doFilter(ServletRequest request, ServletResponse response, FilterChain chain)
			throws IOException, ServletException {

		FilteredRequest requestWrapper = new FilteredRequest((HttpServletRequest) request);
		requestWrapper.getParameter("paramName");
		chain.doFilter(new FilteredRequest(request), response);
	}

	static class FilteredRequest extends HttpServletRequestWrapper {

		public FilteredRequest(ServletRequest request) {
			super((HttpServletRequest) request);
		}

		public String getParameter(String paramName) {
			String value = super.getParameter(paramName);
			return value + "modify";
		}

	}

	public void destroy() {
		// TODO Auto-generated method stub
	}

	public void init(FilterConfig paramFilterConfig) throws ServletException {
		// TODO Auto-generated method stub

	}

}

測試結果如下圖

• URL請求地址
  

• 自定義過濾器修改傳遞參數的數據
  

• Controller中查看傳遞過來的數據
  

接下來我們分析下代碼

Controller 中的 request.getParameter("paramName") 這個調用的是什么？我們看下源碼發現調用的是
package javax.servlet 包 下面的 ServletRequest 抽象接口ServletRequest 中的
public abstract String getParameter(String paramString);

package javax.servlet;

import java.io.BufferedReader;
import java.io.IOException;
import java.io.UnsupportedEncodingException;
import java.util.Enumeration;
import java.util.Locale;
import java.util.Map;

public abstract interface ServletRequest
{
  public abstract Object getAttribute(String paramString);
  
  public abstract Enumeration<String> getAttributeNames();
  
  public abstract String getCharacterEncoding();
  
  public abstract void setCharacterEncoding(String paramString)  throws UnsupportedEncodingException;
  
  public abstract int getContentLength();
  
  public abstract String getContentType();
  
  public abstract ServletInputStream getInputStream()   throws IOException;
  
  public abstract String getParameter(String paramString);
  
  public abstract Enumeration<String> getParameterNames();
  
  public abstract String[] getParameterValues(String paramString);
  
  public abstract Map<String, String[]> getParameterMap();
  
  public abstract String getProtocol();
  
  public abstract String getScheme();
  
  public abstract String getServerName();
  
  public abstract int getServerPort();
  
  public abstract BufferedReader getReader()   throws IOException;
  
  public abstract String getRemoteAddr();
  
  public abstract String getRemoteHost();
  
  public abstract void setAttribute(String paramString, Object paramObject);
  
  public abstract void removeAttribute(String paramString);
  
  public abstract Locale getLocale();
  
  public abstract Enumeration<Locale> getLocales();
  
  public abstract boolean isSecure();
  
  public abstract RequestDispatcher getRequestDispatcher(String paramString);
  
  /**
   * @deprecated
   */
  public abstract String getRealPath(String paramString);
  
  public abstract int getRemotePort();
  
  public abstract String getLocalName();
  
  public abstract String getLocalAddr();
  
  public abstract int getLocalPort();
  
  public abstract ServletContext getServletContext();
  
  public abstract AsyncContext startAsync()  throws IllegalStateException;
  
  public abstract AsyncContext startAsync(ServletRequest paramServletRequest, ServletResponse paramServletResponse)   throws IllegalStateException;
  
  public abstract boolean isAsyncStarted();
  
  public abstract boolean isAsyncSupported();
  
  public abstract AsyncContext getAsyncContext();
  
  public abstract DispatcherType getDispatcherType();
}

接下來我們看下Filter的實現類，

public String getParameter(String paramName) {
	String value = super.getParameter(paramName);
	return value + "modify";
}

我們着重看super.getParameter 這個方法，我們點進去看源碼發現的是 ServletRequestWrapper 類下面的

 public String getParameter(String name)
{
    return request.getParameter(name);
}

然而 public class ServletRequestWrapper implements ServletRequest

綜上所述源頭來源於 ServletRequest 我們在Controller 中的 request.getParameter("paramName") 最后就是找的 ServletRequest

我們來看看HttpServletRequestWrapper 類

public class HttpServletRequestWrapper   extends ServletRequestWrapper   implements HttpServletRequest
 {
   public HttpServletRequestWrapper(HttpServletRequest request)
   {
     super(request);
   }
   
   private HttpServletRequest _getHttpServletRequest() {
   return (HttpServletRequest)super.getRequest();
   }
 
   public String getAuthType()
   {
      return _getHttpServletRequest().getAuthType();
   }
 
   public Cookie[] getCookies()
   {
   return _getHttpServletRequest().getCookies();
   }
 
   public long getDateHeader(String name)
   {
     return _getHttpServletRequest().getDateHeader(name);
   }
  
   public String getHeader(String name)
   {
   return _getHttpServletRequest().getHeader(name);
   }
 
   public Enumeration<String> getHeaders(String name)
   {
     return _getHttpServletRequest().getHeaders(name);
   }
  
   public Enumeration<String> getHeaderNames()
   {
    return _getHttpServletRequest().getHeaderNames();
   }
 
   public int getIntHeader(String name)
   {
   return _getHttpServletRequest().getIntHeader(name);
   }
   
   public String getMethod()
   {
      return _getHttpServletRequest().getMethod();
   }
 
   public String getPathInfo()
   {
     return _getHttpServletRequest().getPathInfo();
   }
   
   public String getPathTranslated()
   {
     return _getHttpServletRequest().getPathTranslated();
   }
 
   public String getContextPath()
   {
   return _getHttpServletRequest().getContextPath();
   }
  
 
   public String getQueryString()
   {
    return _getHttpServletRequest().getQueryString();
   }
 
   public String getRemoteUser()
   {
   return _getHttpServletRequest().getRemoteUser();
   }
 
   public boolean isUserInRole(String role)
   {
   return _getHttpServletRequest().isUserInRole(role);
   }
   
   public Principal getUserPrincipal()
   {
      return _getHttpServletRequest().getUserPrincipal();
   }
   
   public String getRequestedSessionId()
   {
      return _getHttpServletRequest().getRequestedSessionId();
   }
   
   public String getRequestURI()
   {
   return _getHttpServletRequest().getRequestURI();
   }
   
   public StringBuffer getRequestURL()
   {
   return _getHttpServletRequest().getRequestURL();
   }
   
   public String getServletPath()
   {
      return _getHttpServletRequest().getServletPath();
   }
   
 
   public HttpSession getSession(boolean create)
   {
     return _getHttpServletRequest().getSession(create);
   }
   
   public HttpSession getSession()
   {
      return _getHttpServletRequest().getSession();
   }
 
   public boolean isRequestedSessionIdValid()
   {
    return _getHttpServletRequest().isRequestedSessionIdValid();
   }
  
   public boolean isRequestedSessionIdFromCookie()
   {
     return _getHttpServletRequest().isRequestedSessionIdFromCookie();
   }

//省略底下的方法