public class ServletRequestWrapper extends java.lang.Object implements ServletRequest  //

public class ServletResponseWrapper extends java.lang.Object implements ServletResponse  //

public class HttpServletRequestWrapper extends ServletRequestWrapper implements HttpServletRequest  //

public class HttpServletResponseWrapper extends ServletResponseWrapper implements HttpServletResponse  // 

package app10a.filter;

import java.io.IOException;

import java.util.ArrayList;

import java.util.Collection;

import java.util.HashSet;

import java.util.Map;

import java.util.Set;

import javax.servlet.Filter;

import javax.servlet.FilterChain;

import javax.servlet.FilterConfig;

import javax.servlet.ServletException;

import javax.servlet.ServletRequest;

import javax.servlet.ServletResponse;

import javax.servlet.annotation.WebFilter;

import javax.servlet.http.HttpServletRequest;

import javax.servlet.http.HttpServletRequestWrapper;

@WebFilter(filterName = "AutoCorrectFilter", urlPatterns = { "/*" })

public class AutoCorrectFilter implements Filter {

    @Override

    public void destroy() {

    }

    @Override

    public void init(FilterConfig filterConfig) throws ServletException {

    }

    @Override

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

        HttpServletRequest httpServletRequest = (HttpServletRequest) request;

        AutoCorrectHttpServletRequestWrapper wrapper = new AutoCorrectHttpServletRequestWrapper(httpServletRequest);

        filterChain.doFilter(wrapper, response);

    }

    class AutoCorrectHttpServletRequestWrapper extends HttpServletRequestWrapper{  // 内部类

        private HttpServletRequest httpServletRequest;

        public AutoCorrectHttpServletRequestWrapper(HttpServletRequest httpServletRequest) {

            super(httpServletRequest);

            this.httpServletRequest = httpServletRequest;

        }

        @Override

        public String getParameter(String name) {

            return autoCorrect(httpServletRequest.getParameter(name));

        }

        @Override

        public String[] getParameterValues(String name) {

            return autoCorrect(httpServletRequest.getParameterValues(name));

        }

        @Override

        public Map<String, String[]> getParameterMap() {

            final Map<String, String[]> parameterMap = httpServletRequest.getParameterMap();

            Map<String, String[]> newMap = new Map<String, String[]>(){

                @Override

                public void clear() {

                    parameterMap.clear();

                }

                @Override

                public boolean containsKey(Object key) {

                    return parameterMap.containsKey(key);

                }

                @Override

                public boolean containsValue(Object value) {

                    return parameterMap.containsValue(value);

                }

                @Override

                public Set<Entry<String, String[]>> entrySet() {

                    return autoCorrect(parameterMap.entrySet());

                }

                @Override

                public String[] get(Object key) {

                    return autoCorrect(parameterMap.get(key));

                }

                @Override

                public boolean isEmpty() {

                    return parameterMap.isEmpty();

                }

                @Override

                public Set<String> keySet() {

                    return parameterMap.keySet();

                }

                @Override

                public String[] put(String key, String[] value) {

                    return parameterMap.put(key, value);

                }

                @Override

                public void putAll(Map<? extends String, ? extends String[]> map) {

                    parameterMap.putAll(map);

                }

                @Override

                public String[] remove(Object key) {

                    return parameterMap.remove(key);

                }

                @Override

                public int size() {

                    return parameterMap.size();

                }

                @Override

                public Collection<String[]> values() {

                    return autoCorrect(parameterMap.values());

                }

            };

            return newMap;

        }

    }

    private String autoCorrect(String value) {

        if (value == null) {

            return null;

        }

        value = value.trim();

        int length = value.length();

        StringBuilder temp = new StringBuilder();

        boolean lastCharWasSpace = false;

        for (int i = 0; i < length; i++) {

            char c = value.charAt(i);

            if (c == ' ') {

                if (!lastCharWasSpace) {

                    temp.append(c);

                }

                lastCharWasSpace = true;

            } else {

                temp.append(c);

                lastCharWasSpace = false;

            }

        }

        return temp.toString();

    }

    private String[] autoCorrect(String[] values) {

        if (values != null) {

            int length = values.length;

            for (int i = 0; i < length; i++) {

                values[i] = autoCorrect(values[i]);

            }

            return values;

        }

        return null;

    }

    private Collection<String[]> autoCorrect(Collection<String[]> valueCollection){

        Collection<String[]> newCollection = new ArrayList<String[]>();

        for (String[] values : newCollection) {

            newCollection.add(autoCorrect(values));

        }

        return newCollection;

    }

    private Set<Map.Entry<String, String[]>> autoCorrect(Set<Map.Entry<String, String[]>> entrySet){

        Set<Map.Entry<String, String[]>> newSet = new HashSet<Map.Entry<String, String[]>>();

        for (final Map.Entry<String, String[]> entry : entrySet) {

            Map.Entry<String, String[]> newEntry = new Map.Entry<String, String[]>(){

                @Override

                public String getKey() {

                    return entry.getKey();

                }

                @Override

                public String[] getValue() {

                    return autoCorrect(entry.getValue());

                }

                @Override

                public String[] setValue(String[] value) {

                    return entry.setValue(value);

                }

            };

            newSet.add(newEntry);

        }

        return newSet;

    }

}

<!-- test1.jsp -->

<%@ page language="java" contentType="text/html; charset=UTF-8" pageEncoding="UTF-8"%>

<!DOCTYPE html>

<html>

<head>

    <meta charset="UTF-8">

    <title>User Form</title>

</head>

<body>

    <form action="test2.jsp" method="post">

        <table>

            <tr>

                <td>Name: </td>

                <td><input type="text" name="name" /></td>

            </tr>

            <tr>

                <td>Address: </td>

                <td><input type="text" name="address" /></td>

            </tr>

            <tr>

                <td colspan="2"><input type="submit" value="Login"></td>

            </tr>

        </table>

    </form>

</body>

</html>

<!-- test2.jsp -->

<%@ page language="java" contentType="text/html; charset=UTF-8" pageEncoding="UTF-8"%>

<%@ taglib uri="http://java.sun.com/jsp/jstl/functions" prefix="fn" %>

<!DOCTYPE html>

<html>

<head>

    <meta charset="UTF-8">

    <title>Form values</title>

</head>

<body>

    <table>

        <tr>

            <td>Name: </td>

            <td>${param.name } (length: ${fn:length(param.name) })</td>

        </tr>

        <tr>

            <td>Address: </td>

            <td>${param.address } (length:${fn:length(param.address) })</td>

        </tr>

    </table>

</body>

</html>