HttpServletRequestWrapper 用法

HttpServletRequestWrapper

 

Filter能在request到达servlet的服务方法之前拦截HttpServletRequest对象，而在服务方 法转移控制后又能拦截HttpServletResponse对象。

你可以使用filter来实现特定的任务，比如验证用户输入，以及压缩web内容。但HttpServletRequest对象的参数是不可改变的，这极大地缩减了filter的应用范围。至少在一半的时间里，你希望可以改变准备传送给 filter的对象。
幸运的是，尽管你不能改变不变对象本身，但你却可以通过使用装饰模式来改变其状态。 

 

Example1：
一个删除空白字符的Filter 

 

HttpServerletRequest装饰类

 

import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletRequestWrapper;

public final class MyRequestWrapper extends HttpServletRequestWrapper {
    public MyRequestWrapper(HttpServletRequest servletRequest) {
        super(servletRequest);
    }

    public String[] getParameterValues(String parameter) {
        String[] results = super.getParameterValues(parameter);
        if (results == null) {
            return null;
        }
        int count = results.length;
        String[] trimResults = new String[count];

        for (int i = 0; i < count; i++) {
            trimResults[i] = results[i].trim();
        }
        return trimResults;
    }
}

 

如何载获Http请求并装饰HttpServletRequest对象

public class MyFilter implements Filter {
    private FilterConfig filterConfig;

    public void init(FilterConfig filterConfig) throws ServletException {
        System.out.println("Filter initialized");
        this.filterConfig = filterConfig;
    }

    public void destroy() {
        System.out.println("Filter destroyed");
        this.filterConfig = null;
    }

    public void doFilter(ServletRequest request, ServletResponse response,
        FilterChain chain) throws IOException, ServletException {
        chain.doFilter(new MyRequestWrapper((HttpServletRequest) request),
            response);
    }
}

 

 

Example2：

通过HttpServletRequestWrapper（装饰模式的应用）来解决中文乱码问题

自定义请求包装器包装请求，将字符编码转换的工作添加到getParameter()方法中

mport java.io.UnsupportedEncodingException;  
import java.net.URLDecoder;  
  
import javax.servlet.http.HttpServletRequest;  
import javax.servlet.http.HttpServletRequestWrapper;  
  
public class GetHttpServletRequestWrapper extends HttpServletRequestWrapper {  
  
    private String charset = "UTF-8";  
  
    public GetHttpServletRequestWrapper(HttpServletRequest request) {  
        super(request);  
    }  
  
    /** 
     * 获得被装饰对象的引用和采用的字符编码 
     * @param request 
     * @param charset 
     */  
    public GetHttpServletRequestWrapper(HttpServletRequest request,  
            String charset) {  
        super(request);  
        this.charset = charset;  
    }  
  
    /** 
     * 实际上就是调用被包装的请求对象的getParameter方法获得参数，然后再进行编码转换 
     */  
    public String getParameter(String name) {  
        String value = super.getParameter(name);  
        value = value == null ? null : convert(value);  
        return value;  
    }  
  
    public String convert(String target) {  
        System.out.println("编码转换之前：" + target);  
        try {  
            return new String(target.trim().getBytes("ISO-8859-1"), charset);  
        } catch (UnsupportedEncodingException e) {  
            return target;  
        }  
    }  
  
} 

 

    public void doFilter(ServletRequest request, ServletResponse response,  
                FilterChain chain) throws IOException, ServletException {  
            //设置请求响应字符编码  
            request.setCharacterEncoding(charset);  
            response.setCharacterEncoding(charset);  
            //新增加的代码          
            HttpServletRequest req = (HttpServletRequest)request;  
              
            if(req.getMethod().equalsIgnoreCase("get"))  
            {  
                req = new GetHttpServletRequestWrapper(req,charset);  
            }  
              
            System.out.println("----请求被"+config.getFilterName()+"过滤");  
            //传递给目标servlet或jsp的实际上时包装器对象的引用，而不是原始的HttpServletRequest对象  
            chain.doFilter(req, response);  
              
            System.out.println("----响应被"+config.getFilterName()+"过滤");  
      
        }  

 这样一来，在servlet中调用包装器的getParameters方法来获取参数，就已经完成了字符编码的转换过程，我们就不需要在每次获取参数时来进行字符编码转换了。

例子来源：http://www.iteye.com/topic/483158