使用HttpServletRequestWrapper在filter修改request参数

javax.servlet.ServletRequest中的

Map 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
     *  null 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。 

"<%=request.getContextPath()%>/sa?userid=123456789&username=rensanning">Click me!!!

第二步： 
新作Filter类：ParameterFilter，配置web.xml 

<filter-mapping>
    <filter-name>ParameterFilterfilter-name>
    <url-pattern>/*url-pattern>
filter-mapping>

在doFilter方法中包装request，设置新参数值。 

Map m = new HashMap(req.getParameterMap());
m.put("name", new String[]{"newname"});
req = new ParameterRequestWrapper((HttpServletRequest)req, m);

chain.doFilter(req, res);

包装类代码如下： 

class ParameterRequestWrapper extends HttpServletRequestWrapper {

    private Map params;

    public ParameterRequestWrapper(HttpServletRequest request,
            Map newParams) {
        super(request);

        this.params = newParams;
    }

    @Override
    public String getParameter(String name) {
        String result = "";

        Object v = params.get(name);
        if (v == null) {
            result = null;
        } else if (v instanceof String[]) {
            String[] strArr = (String[]) v;
            if (strArr.length > 0) {
                result =  strArr[0];
            } else {
                result = null;
            }
        } else if (v instanceof String) {
            result = (String) v;
        } else {
            result =  v.toString();
        }

        return result;
    }

    @Override
    public Map getParameterMap() {
        return params;
    }

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

    @Override
    public String[] getParameterValues(String name) {
        String[] result = null;

        Object v = params.get(name);
        if (v == null) {
            result =  null;
        } else if (v instanceof String[]) {
            result =  (String[]) v;
        } else if (v instanceof String) {
            result =  new String[] { (String) v };
        } else {
            result =  new String[] { v.toString() };
        }

        return result;
    }

}

第三步： 
sa的Servlet中，doGet()方法做forward跳转。 

RequestDispatcher rd = getServletContext().getRequestDispatcher("/sb?myname=rensanning&mycountry=china");

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： 

<filter-mapping>
    <filter-name>ParameterFilterfilter-name>
    <url-pattern>/*url-pattern>
    <dispatcher>REQUESTdispatcher>
    <dispatcher>FORWARDdispatcher>
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： 

class ParameterRequestWrapper extends HttpServletRequestWrapper {

    private Map params;

    public ParameterRequestWrapper(HttpServletRequest request,
            Map newParams) {
        super(request);

        this.params = newParams;

        // RequestDispatcher.forward parameter
        renewParameterMap(request);
    }

    @Override
    public String getParameter(String name) {
        String result = "";

        Object v = params.get(name);
        if (v == null) {
            result = null;
        } else if (v instanceof String[]) {
            String[] strArr = (String[]) v;
            if (strArr.length > 0) {
                result =  strArr[0];
            } else {
                result = null;
            }
        } else if (v instanceof String) {
            result = (String) v;
        } else {
            result =  v.toString();
        }

        return result;
    }

    @Override
    public Map getParameterMap() {
        return params;
    }

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

    @Override
    public String[] getParameterValues(String name) {
        String[] result = null;

        Object v = params.get(name);
        if (v == null) {
            result =  null;
        } else if (v instanceof String[]) {
            result =  (String[]) v;
        } else if (v instanceof String) {
            result =  new String[] { (String) v };
        } else {
            result =  new String[] { v.toString() };
        }

        return result;
    }

    private void renewParameterMap(HttpServletRequest req) {

        String queryString = req.getQueryString();

        if (queryString != null && queryString.trim().length() > 0) {
            String[] params = queryString.split("&");

            for (int i = 0; i < params.length; i++) {
                int splitIndex = params[i].indexOf("=");
                if (splitIndex == -1) {
                    continue;
                }

                String key = params[i].substring(0, splitIndex);

                if (!this.params.containsKey(key)) {
                    if (splitIndex < params[i].length()) {
                        String value = params[i].substring(splitIndex + 1);
                        this.params.put(key, new String[] { value });
                    }
                }
            }
        }
    }

}

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 params;

    public ParameterRequestWrapper(HttpServletRequest request, Map 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 getParameterMap() {
        return params;
    }

    @Override
    public Enumeration 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 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, 

• ForwardParameter.rar (4.8 KB)

 

http://rensanning.iteye.com/blog/1706208