• 使用HttpServletRequestWrapper在filter修改request参数

    javax.servlet.ServletRequest中的
    Map<String, String[]> parameterMap = request.getParameterMap();不能被修改，原因如下：
    org/apache/tomcat/embed/tomcat-embed-core/8.0.32/tomcat-embed-core-8.0.32-sources.jar!/org/apache/catalina/util/ParameterMap.java
        /**
     * Associate the specified value with the specified key in this map.  If
     * the map previously contained a mapping for this key, the old value is
     * replaced.
     *
     * @param key Key with which the specified value is to be associated
     * @param value Value to be associated with the specified key
     *
     * @return The previous value associated with the specified key, or
     *  <code>null</code> if there was no mapping for key
     *
     * @exception IllegalStateException if this map is currently locked
     */
    @Override
    public V put(K key, V value) {

        if (locked)
            throw new IllegalStateException
                (sm.getString("parameterMap.locked"));
        return (super.put(key, value));

    }

    https://my.oschina.net/cwalet/blog/35431

     
    处理过程： 
    （1）页面提交请求“/sa?userid=123456789&username=rensanning” 
    （2）通过Filter处理加入新参数“name=newname” 
    （3）sa的Servlet中forward到“/sb?myname=rensanning&mycountry=china” 
    （4）sb的Servlet中生成页面输出所有参数：userid、username、myname、mycountry、name 

    第一步： 
    最简单，在页面上先输出一个href为改地址的链接即可。 
     
    1. <a href="<%=request.getContextPath()%>/sa?userid=123456789&username=rensanning">Click me!!!</a>  


    第二步： 
    新作Filter类：ParameterFilter，配置web.xml 
     
    1. <filter-mapping>  
    2.     <filter-name>ParameterFilter</filter-name>  
    3.     <url-pattern>/*</url-pattern>  
    4. </filter-mapping>  


    在doFilter方法中包装request，设置新参数值。 
     
    1. Map<String,String[]> m = new HashMap<String,String[]>(req.getParameterMap());  
    2. m.put("name", new String[]{"newname"});  
    3. req = new ParameterRequestWrapper((HttpServletRequest)req, m);  
    4.   
    5. chain.doFilter(req, res);  


    包装类代码如下： 
     
    1. class ParameterRequestWrapper extends HttpServletRequestWrapper {  
    2.   
    3.     private Map<String, String[]> params;  
    4.   
    5.     public ParameterRequestWrapper(HttpServletRequest request,  
    6.             Map<String, String[]> newParams) {  
    7.         super(request);  
    8.           
    9.         this.params = newParams;  
    10.     }  
    11.   
    12.     @Override  
    13.     public String getParameter(String name) {  
    14.         String result = "";  
    15.           
    16.         Object v = params.get(name);  
    17.         if (v == null) {  
    18.             result = null;  
    19.         } else if (v instanceof String[]) {  
    20.             String[] strArr = (String[]) v;  
    21.             if (strArr.length > 0) {  
    22.                 result =  strArr[0];  
    23.             } else {  
    24.                 result = null;  
    25.             }  
    26.         } else if (v instanceof String) {  
    27.             result = (String) v;  
    28.         } else {  
    29.             result =  v.toString();  
    30.         }  
    31.           
    32.         return result;  
    33.     }  
    34.   
    35.     @Override  
    36.     public Map getParameterMap() {  
    37.         return params;  
    38.     }  
    39.   
    40.     @Override  
    41.     public Enumeration getParameterNames() {  
    42.         return new Vector(params.keySet()).elements();  
    43.     }  
    44.   
    45.     @Override  
    46.     public String[] getParameterValues(String name) {  
    47.         String[] result = null;  
    48.           
    49.         Object v = params.get(name);  
    50.         if (v == null) {  
    51.             result =  null;  
    52.         } else if (v instanceof String[]) {  
    53.             result =  (String[]) v;  
    54.         } else if (v instanceof String) {  
    55.             result =  new String[] { (String) v };  
    56.         } else {  
    57.             result =  new String[] { v.toString() };  
    58.         }  
    59.           
    60.         return result;  
    61.     }  
    62.   
    63. }  


    第三步： 
    sa的Servlet中，doGet()方法做forward跳转。 
    Java代码  收藏代码
    1. RequestDispatcher rd = getServletContext().getRequestDispatcher("/sb?myname=rensanning&mycountry=china");  
    2.   
    3. rd.forward(request, response);  


    第四步： 
    sb的Servlet中生成页面输出所有QueryString和ParameterMap的参数。（代码略） 

    问题： 
    （1）Filter也只执行了一次 

    由于RequestDispatcher.forward是Servlet之间的跳转，所以默认不走Filter。在Servlet2.4规范中定义了可以在web.xml中配置： 
    Xml代码  收藏代码
    1. <filter-mapping>  
    2.     <filter-name>ParameterFilter</filter-name>  
    3.     <url-pattern>/*</url-pattern>  
    4.     <dispatcher>REQUEST</dispatcher>  
    5.     <dispatcher>FORWARD</dispatcher>  
    6. </filter-mapping>  


    （2）结果的QueryString中存在forward时URL的两个参数（myname、mycountry），而ParameterMap中没有。

    forward时QueryString中的参数未被放入ParameterMap？？？ 

    如下修改wrapper类： 
    Java代码  收藏代码
    1. class ParameterRequestWrapper extends HttpServletRequestWrapper {  
    2.   
    3.     private Map<String, String[]> params;  
    4.   
    5.     public ParameterRequestWrapper(HttpServletRequest request,  
    6.             Map<String, String[]> newParams) {  
    7.         super(request);  
    8.           
    9.         this.params = newParams;  
    10.   
    11.         // RequestDispatcher.forward parameter  
    12.         renewParameterMap(request);  
    13.     }  
    14.   
    15.     @Override  
    16.     public String getParameter(String name) {  
    17.         String result = "";  
    18.           
    19.         Object v = params.get(name);  
    20.         if (v == null) {  
    21.             result = null;  
    22.         } else if (v instanceof String[]) {  
    23.             String[] strArr = (String[]) v;  
    24.             if (strArr.length > 0) {  
    25.                 result =  strArr[0];  
    26.             } else {  
    27.                 result = null;  
    28.             }  
    29.         } else if (v instanceof String) {  
    30.             result = (String) v;  
    31.         } else {  
    32.             result =  v.toString();  
    33.         }  
    34.           
    35.         return result;  
    36.     }  
    37.   
    38.     @Override  
    39.     public Map getParameterMap() {  
    40.         return params;  
    41.     }  
    42.   
    43.     @Override  
    44.     public Enumeration getParameterNames() {  
    45.         return new Vector(params.keySet()).elements();  
    46.     }  
    47.   
    48.     @Override  
    49.     public String[] getParameterValues(String name) {  
    50.         String[] result = null;  
    51.           
    52.         Object v = params.get(name);  
    53.         if (v == null) {  
    54.             result =  null;  
    55.         } else if (v instanceof String[]) {  
    56.             result =  (String[]) v;  
    57.         } else if (v instanceof String) {  
    58.             result =  new String[] { (String) v };  
    59.         } else {  
    60.             result =  new String[] { v.toString() };  
    61.         }  
    62.           
    63.         return result;  
    64.     }  
    65.   
    66.     private void renewParameterMap(HttpServletRequest req) {  
    67.   
    68.         String queryString = req.getQueryString();  
    69.   
    70.         if (queryString != null && queryString.trim().length() > 0) {  
    71.             String[] params = queryString.split("&");  
    72.   
    73.             for (int i = 0; i < params.length; i++) {  
    74.                 int splitIndex = params[i].indexOf("=");  
    75.                 if (splitIndex == -1) {  
    76.                     continue;  
    77.                 }  
    78.                   
    79.                 String key = params[i].substring(0, splitIndex);  
    80.   
    81.                 if (!this.params.containsKey(key)) {  
    82.                     if (splitIndex < params[i].length()) {  
    83.                         String value = params[i].substring(splitIndex + 1);  
    84.                         this.params.put(key, new String[] { value });  
    85.                     }  
    86.                 }  
    87.             }  
    88.         }  
    89.     }  
    90.   
    91. }  
    import javax.servlet.ServletRequest;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletRequestWrapper;
import java.util.Enumeration;
import java.util.Map;
import java.util.Vector;

/**
 * Created by MyWorld on 2016/9/25.
 */
public class ParameterRequestWrapper extends HttpServletRequestWrapper {
    /**
     * Constructs a request object wrapping the given request.
     *
     * @param request The request to wrap
     * @throws IllegalArgumentException if the request is null
     * http://www.cnblogs.com/softidea/p/5903873.html
     *
     */
    private Map<String, String[]> params;

    public ParameterRequestWrapper(HttpServletRequest request, Map<String, String[]> params) {
        super(request);
        this.params = params;
        addHeaderInfoToParams(request);
    }

    private void addHeaderInfoToParams(HttpServletRequest request) {
        request.getHeader("_pid");

    }

    @Override
    public String getParameter(String name) {
        String[] values = getParameterValues(name);
        if (values == null || values.length == 0) {
            return null;
        } else {
            return values[0];
        }
    }

    @Override
    public Map<String, String[]> getParameterMap() {
        return params;
    }

    @Override
    public Enumeration<String> getParameterNames() {
        return new Vector(params.keySet()).elements();
    }

    @Override
    public String[] getParameterValues(String name) {
        String[] values = params.get(name);
        if (values == null) {
            return null;
        } else {
            return values;
        }
    }


}
    import javax.servlet.*;
import javax.servlet.http.HttpServletRequest;
import java.io.IOException;
import java.util.HashMap;
import java.util.Map;

/**
 * Created by MyWorld on 2016/9/25.
 */
public class AddExtraToParamsFilter implements Filter {
    @Override
    public void init(FilterConfig filterConfig) throws ServletException {
    }

    @Override
    public void doFilter(ServletRequest request, ServletResponse response, FilterChain chain) throws IOException, ServletException {
        Map<String, String[]> params = new HashMap<>(request.getParameterMap());

        HttpServletRequest httpServletRequest = (HttpServletRequest) request;
        String pid = httpServletRequest.getHeader("_pid");
        if (pid != null) {
            params.put("pid", new String[]{pid});
        }
        request = new ParameterRequestWrapper(httpServletRequest, params);
        chain.doFilter(request, response);
    }

    @Override
    public void destroy() {
    }
}
     

    再次运行代码： 
    （1）Filter进入两次： 
    引用
    URL:http://localhost:8080/t/sa 
    ***-----From QueryString-----*** 
    userid=123456789 
    username=rensanning 
    ***-----From ParameterMap-----*** 
    username=rensanning, 
    userid=123456789,


    引用
    URL:http://localhost:8080/t/sb 
    ***-----From QueryString-----*** 
    myname=rensanning 
    mycountry=china 
    ***-----From ParameterMap-----*** 
    username=rensanning, 
    name=newname, 
    userid=123456789,


    （2）最终页面结果： 
    引用

    ***-----From QueryString-----*** 

    myname=rensanning 

    mycountry=china 




    ***-----From ParameterMap-----*** 

    username=rensanning, 

    name=newname, 

    userid=123456789, 

    mycountry=china, 

    myname=rensanning, 

    http://rensanning.iteye.com/blog/1706208
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  • 原文地址：https://www.cnblogs.com/softidea/p/5904831.html
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