12.1、Decorator模式
即使没有某一个对象的类的源代码，甚至即便这个类是声明为final的，Decorator模式和Wrapper模式都允许装饰或包装这个对象。
Decorator模式适用于无法使用继承的情况（比如，所指对象的类为final），或者你不想亲自创建对象，而是想从另一个子系统中获取。例如，Servlet容器创建了一个ServletRequest和一个ServletResponse，并将他们传给Servlet的service方法。改变ServletRequest和ServletResponse行为的唯一方法是将他们包在其他对象中。唯一必须满足的条件是，被装饰对象的类要实现一个接口，并且要包装的方法必须从这个接口处继承。
12.2、Servlet Wrapper类
Servlet API中提供了4个类，他们很少用到，但是功能非常强大，分别是：ServletRequestWrapper、ServletResponseWrapper，以及HttpServletRequestWrapper和HttpServletResponseWrapper。
ServletRequestWrapper使用起来非常方便，由于它为调用被包装ServletRequest中的对等方法的每一个方法都提供了默认实现。通过继承则只好直接实现ServletRequest，并为接口中的每一个方法都提供实现。
12.3、范例：AutoCorrect过滤器
在web应用程序中，用户经常会在输入值时，在其前面或者后面添加一些空格，甚至在词与词之间也会有多余空格。你又不想到应用程序的逐个Servlet中进行检查并删除多余的空格。那么本届介绍的AutoCorrect过滤器的特性就可以帮你完成这些工作。这个过滤器中包含一个HttpServletRequestWrapper的子类，命名为AutoCorrectHttpServletRequestWrapper，并覆盖返回一个或多个参数值的下列方法：getParameter、getParameterValues和getParameterMap。
AutoCorrectFilter.java
package 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() {
// TODO Auto-generated method stub
}
@Override
public void init(FilterConfig arg0) throws ServletException {
// TODO Auto-generated method stub
}
@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{
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) {
// TODO Auto-generated method stub
return autoCorrect(httpServletRequest.getParameterValues(name));
}
@Override
public Map<String, String[]> getParameterMap() {
// TODO Auto-generated method stub
final Map<String, String[]> parameterMap = httpServletRequest.getParameterMap() ;
Map<String, String[]> newMap = new Map<String, String[]>(){
@Override
public int size() {
return parameterMap.size();
}
@Override
public boolean isEmpty() {
return parameterMap.isEmpty();
}
@Override
public boolean containsKey(Object key) {
return parameterMap.containsKey(key);
}
@Override
public boolean containsValue(Object value) {
return parameterMap.containsValue(value);
}
@Override
public String[] get(Object key) {
return autoCorrect(parameterMap.get(key));
}
@Override
public String[] put(String key, String[] value) {
return parameterMap.put(key, value);
}
@Override
public String[] remove(Object key) {
return parameterMap.remove(key);
}
@Override
public void putAll(Map<? extends String, ? extends String[]> m) {
parameterMap.putAll(m);
}
@Override
public void clear() {
parameterMap.clear();
}
@Override
public Set<String> keySet() {
return parameterMap.keySet();
}
@Override
public Collection<String[]> values() {
return autoCorrect(parameterMap.values());
}
@Override
public Set<java.util.Map.Entry<String, String[]>> entrySet() {
return autoCorrect(parameterMap.entrySet());
}
} ;
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 ;
}
@SuppressWarnings("unused")
private Collection<String[]> autoCorrect(Collection<String[]> valueCollection){
Collection<String[]> newCollection = new ArrayList<String[]>() ;
for(String[] values : valueCollection){
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" import="java.util.*" pageEncoding="UTF-8"%>
<%
String path = request.getContextPath();
String basePath = request.getScheme()+"://"+request.getServerName()+":"+request.getServerPort()+path+"/";
%>
<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN">
<html>
<head>
<base href="<%=basePath%>">
<title>User Form</title>
<meta http-equiv="pragma" content="no-cache">
<meta http-equiv="cache-control" content="no-cache">
<meta http-equiv="expires" content="0">
<meta http-equiv="keywords" content="keyword1,keyword2,keyword3">
<meta http-equiv="description" content="This is my page">
<!--
<link rel="stylesheet" type="text/css" href="styles.css">
-->
</head>
<body>
<form action="test2.jsp" method="post">
<table>
<tr>
<td>Name:</td>
<td><input name="name"/></td>
</tr>
<tr>
<td>Address:</td>
<td><input name="address"/></td>
</tr>
<tr>
<td colspan="2">
<input type="submit" value="Login"/>
</td>
</tr>
</table>
</form>
</body>
</html>
test2.jsp
<%@ page language="java" import="java.util.*" pageEncoding="UTF-8"%>
<%@ taglib prefix="fn" uri="http://java.sun.com/jsp/jstl/functions" %>
<%
String path = request.getContextPath();
String basePath = request.getScheme()+"://"+request.getServerName()+":"+request.getServerPort()+path+"/";
%>
<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN">
<html>
<head>
<base href="<%=basePath%>">
<title>Form Values</title>
<meta http-equiv="pragma" content="no-cache">
<meta http-equiv="cache-control" content="no-cache">
<meta http-equiv="expires" content="0">
<meta http-equiv="keywords" content="keyword1,keyword2,keyword3">
<meta http-equiv="description" content="This is my page">
<!--
<link rel="stylesheet" type="text/css" href="styles.css">
-->
</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>
运行结果：
时间： 2024-11-05 15:57:23