- 編寫子類,覆蓋需增強的方法。
- 使用Decorator設計模式對方法進行增強。
在閻宏博士的《JAVA與模式》一書中開頭是這樣描述裝飾(Decorator)模式的:裝飾模式又名包裝(Wrapper)模式。裝飾模式以對客戶端透明的方式擴展對象的功能,是繼承關係的一個替代方案。裝飾模式是在不必改變原類文件和使用繼承的情況下,動態的擴展一個對象的功能。它是通過創建一個包裝對象,也就是裝飾來包裹真實的對象。
那麼在實際應用中遇到需增強對象的方法時,到底選用哪種方式比較好呢?這個沒有具體的定式,只能是根據具體的需求來採用具體的方式,不過有一種情況下,必須使用Decorator設計模式:即被增強的對象,開發人員只能得到它的對象,無法得到它的class文件。比如request、response對象,開發人員之所以在servlet中能通過sun公司定義的HttpServletRequest\response接口去操作這些對象,是因爲Tomcat服務器廠商編寫了request、response接口的實現類。web服務器在調用servlet時,會用這些接口的實現類創建出對象,然後傳遞給servlet程序。此種情況下,由於開發人員根本不知道服務器廠商編寫的request、response接口的實現類是哪個?在程序中只能拿到服務器廠商提供的對象,因此就只能採用Decorator設計模式對這些對象進行增強。
1.2、Decorator設計模式的實現
1.首先看需要被增強對象繼承了什麼接口或父類,編寫一個類也去繼承這些接口或父類。
2.在類中定義一個變量,變量類型即需增強對象的類型。
3.在類中定義一個構造函數,接收需增強的對象。
4.覆蓋需增強的方法,編寫增強的代碼。
二、使用Decorator設計模式增強request對象
Servlet API 中提供了一個request對象的Decorator設計模式的默認實現類HttpServletRequestWrapper,HttpServletRequestWrapper 類實現了request 接口中的所有方法,但這些方法的內部實現都是僅僅調用了一下所包裝的的 request 對象的對應方法,以避免用戶在對request對象進行增強時需要實現request接口中的所有方法。
2.1、使用Decorator模式包裝request對象解決get和post請求方式下的中文亂碼問題
編寫一個用於處理中文亂碼的過濾器CharacterEncodingFilter,代碼如下:
import java.io.IOException;
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.http.HttpServletRequest;
import javax.servlet.http.HttpServletRequestWrapper;
import javax.servlet.http.HttpServletResponse;
/**
* @ClassName: CharacterEncodingFilter
* @Description: 此過濾器用來解決解決get、post請求方式下的中文亂碼問題
* @author: 孤傲蒼狼
* @date: 2014-8-31 下午11:09:37
*
*/
public class CharacterEncodingFilter implements Filter {
private FilterConfig filterConfig = null;
//設置默認的字符編碼
private String defaultCharset = "UTF-8";
public void doFilter(ServletRequest req, ServletResponse resp,
FilterChain chain) throws IOException, ServletException {
HttpServletRequest request = (HttpServletRequest) req;
HttpServletResponse response = (HttpServletResponse) resp;
//得到在web.xml中配置的字符編碼
String charset = filterConfig.getInitParameter("charset");
if(charset==null){
charset = defaultCharset;
}
request.setCharacterEncoding(charset);
response.setCharacterEncoding(charset);
response.setContentType("text/html;charset="+charset);
MyCharacterEncodingRequest requestWrapper = new MyCharacterEncodingRequest(request);
chain.doFilter(requestWrapper, response);
}
public void init(FilterConfig filterConfig) throws ServletException {
//得到過濾器的初始化配置信息
this.filterConfig = filterConfig;
}
public void destroy() {
}
}
/**
* @ClassName: MyCharacterEncodingRequest
* @Description: Servlet API中提供了一個request對象的Decorator設計模式的默認實現類HttpServletRequestWrapper,
* (HttpServletRequestWrapper類實現了request接口中的所有方法,但這些方法的內部實現都是僅僅調用了一下所包裝的的 request對象的對應方法)
* 以避免用戶在對request對象進行增強時需要實現request接口中的所有方法。
* 所以當需要增強request對象時,只需要寫一個類繼承HttpServletRequestWrapper類,然後在重寫需要增強的方法即可
* @author: 孤傲蒼狼
* @date: 2014-9-2 下午10:42:57
* 1.實現與被增強對象相同的接口
2、定義一個變量記住被增強對象
3、定義一個構造函數,接收被增強對象
4、覆蓋需要增強的方法
5、對於不想增強的方法,直接調用被增強對象(目標對象)的方法
*/
class MyCharacterEncodingRequest extends HttpServletRequestWrapper{
//定義一個變量記住被增強對象(request對象是需要被增強的對象)
private HttpServletRequest request;
//定義一個構造函數,接收被增強對象
public MyCharacterEncodingRequest(HttpServletRequest request) {
super(request);
this.request = request;
}
/* 覆蓋需要增強的getParameter方法
* @see javax.servlet.ServletRequestWrapper#getParameter(java.lang.String)
*/
@Override
public String getParameter(String name) {
try{
//獲取參數的值
String value= this.request.getParameter(name);
if(value==null){
return null;
}
//如果不是以get方式提交數據的,就直接返回獲取到的值
if(!this.request.getMethod().equalsIgnoreCase("get")) {
return value;
}else{
//如果是以get方式提交數據的,就對獲取到的值進行轉碼處理
value = new String(value.getBytes("ISO8859-1"),this.request.getCharacterEncoding());
return value;
}
}catch (Exception e) {
throw new RuntimeException(e);
}
}
}
在web.xml文件中配置CharacterEncodingFilter:
<!--配置字符過濾器,解決get、post請求方式下的中文亂碼問題-->
<filter>
<filter-name>CharacterEncodingFilter</filter-name>
<filter-class>di.cha.filter.CharacterEncodingFilter</filter-class>
</filter>
<filter-mapping>
<filter-name>CharacterEncodingFilter</filter-name>
<url-pattern>/*</url-pattern>
</filter-mapping>
2.2、使用Decorator模式包裝request對象實現html標籤轉義功能
編寫一個html轉義過濾器,代碼如下:
import java.io.IOException;
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.http.HttpServletRequest;
import javax.servlet.http.HttpServletRequestWrapper;
import javax.servlet.http.HttpServletResponse;
/**
* @ClassName: HtmlFilter
* @Description: html轉義過濾器
* @author: 孤傲蒼狼
* @date: 2014-9-2 下午11:28:41
*
*/
public class HtmlFilter implements Filter {
public void doFilter(ServletRequest req, ServletResponse resp,
FilterChain chain) throws IOException, ServletException {
HttpServletRequest request = (HttpServletRequest) req;
HttpServletResponse response = (HttpServletResponse) resp;
MyHtmlRequest myrequest = new MyHtmlRequest(request);
chain.doFilter(myrequest, response);
}
public void destroy() {
}
public void init(FilterConfig filterConfig) throws ServletException {
}
}
/**
* @ClassName: MyHtmlRequest
* @Description: 使用Decorator模式包裝request對象,實現html標籤轉義功能
* @author: 孤傲蒼狼
* @date: 2014-9-2 下午11:29:09
*
*/
class MyHtmlRequest extends HttpServletRequestWrapper {
private HttpServletRequest request;
public MyHtmlRequest(HttpServletRequest request) {
super(request);
this.request = request;
}
/* 覆蓋需要增強的getParameter方法
* @see javax.servlet.ServletRequestWrapper#getParameter(java.lang.String)
*/
@Override
public String getParameter(String name) {
String value = this.request.getParameter(name);
if (value == null) {
return null;
}
//調用filter轉義value中的html標籤
return filter(value);
}
/**
* @Method: filter
* @Description: 過濾內容中的html標籤
* @Anthor:孤傲蒼狼
* @param message
* @return
*/
public String filter(String message) {
if (message == null){
return null;
}
char content[] = new char[message.length()];
message.getChars(0, message.length(), content, 0);
StringBuffer result = new StringBuffer(content.length + 50);
for (int i = 0; i < content.length; i++) {
switch (content[i]) {
case '<':
result.append("<");
break;
case '>':
result.append(">");
break;
case '&':
result.append("&");
break;
case '"':
result.append(""");
break;
default:
result.append(content[i]);
}
}
return result.toString();
}
}
在web.xml文件中配置HtmlFilter:
<!--配置Html過濾器,轉義內容中的html標籤-->
<filter>
<filter-name>HtmlFilter</filter-name>
<filter-class>di.cha.filter.HtmlFilter</filter-class>
</filter>
<filter-mapping>
<filter-name>HtmlFilter</filter-name>
<url-pattern>/*</url-pattern>
</filter-mapping>
編寫jsp測試頁面,如下:
<%@ page language="java" import="java.util.*" pageEncoding="UTF-8"%>
<!DOCTYPE HTML>
<html>
<head>
<title>html過濾器測試</title>
</head>
<body>
<form action="${pageContext.request.contextPath}/servlet/ServletDemo2" method="post">
留言:
<textarea rows="8" cols="70" name="message">
<script type="text/javascript">
while(true){
alert("死循環了,我會不停地彈出了");
}
</script>
<a href="http://www.cnblogs.com">訪問博客園</a>
</textarea>
<input type="submit" value="發表">
</form>
</body>
</html>
編寫處理用戶請求的ServletDemo2:
import java.io.IOException;
import javax.servlet.ServletException;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
public class ServletDemo2 extends HttpServlet {
public void doGet(HttpServletRequest request, HttpServletResponse response)
throws ServletException, IOException {
//獲取用戶輸入的內容
String message = request.getParameter("message");
response.getWriter().write("您上次的留言是:<br/>" + message);
}
public void doPost(HttpServletRequest request, HttpServletResponse response)
throws ServletException, IOException {
doGet(request, response);
}
}
測試結果如下:
從運行結果中可以看到,所有的html標籤都被轉義輸出了。
2.3、使用Decorator模式包裝request對象實現敏感字符過濾功能
編寫一個敏感字符過濾器,代碼如下:
import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStream;
import java.io.InputStreamReader;
import java.io.UnsupportedEncodingException;
import java.util.ArrayList;
import java.util.List;
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.http.HttpServletRequest;
import javax.servlet.http.HttpServletRequestWrapper;
import javax.servlet.http.HttpServletResponse;
/**
* @ClassName: DirtyFilter
* @Description: 敏感詞過濾器
* @author: 孤傲蒼狼
* @date: 2014-9-6 上午10:43:11
*
*/
public class DirtyFilter implements Filter {
private FilterConfig config = null;
@Override
public void init(FilterConfig filterConfig) throws ServletException {
this.config = filterConfig;
}
@Override
public void doFilter(ServletRequest req, ServletResponse resp,
FilterChain chain) throws IOException, ServletException {
HttpServletRequest request = (HttpServletRequest) req;
HttpServletResponse response = (HttpServletResponse) resp;
DirtyRequest dirtyrequest = new DirtyRequest(request);
chain.doFilter(dirtyrequest, response);
}
@Override
public void destroy() {
}
/**
* @Method: getDirtyWords
* @Description: 獲取敏感字符
* @Anthor:孤傲蒼狼
*
* @return
*/
private List<String> getDirtyWords(){
List<String> dirtyWords = new ArrayList<String>();
String dirtyWordPath = config.getInitParameter("dirtyWord");
InputStream inputStream = config.getServletContext().getResourceAsStream(dirtyWordPath);
InputStreamReader is = null;
try {
is = new InputStreamReader(inputStream,"UTF-8");
} catch (UnsupportedEncodingException e2) {
e2.printStackTrace();
}
BufferedReader reader = new BufferedReader(is);
String line;
try {
while ((line = reader.readLine())!= null) {//如果 line爲空說明讀完了
dirtyWords.add(line);
}
} catch (IOException e) {
e.printStackTrace();
}
return dirtyWords;
}
/**
* @ClassName: DirtyRequest
* @Description: 使用Decorator模式包裝request對象,實現敏感字符過濾功能
* @author: 孤傲蒼狼
* @date: 2014-9-6 上午11:56:35
*
*/
class DirtyRequest extends HttpServletRequestWrapper{
private List<String> dirtyWords = getDirtyWords();
private HttpServletRequest request;
public DirtyRequest(HttpServletRequest request) {
super(request);
this.request = request;
}
/* 重寫getParameter方法,實現對敏感字符的過濾
* @see javax.servlet.ServletRequestWrapper#getParameter(java.lang.String)
*/
@Override
public String getParameter(String name) {
String value = this.request.getParameter(name);
if(value==null){
return null;
}
for(String dirtyWord : dirtyWords){
if(value.contains(dirtyWord)){
System.out.println("內容中包含敏感詞:"+dirtyWord+",將會被替換成****");
//替換敏感字符
value = value.replace(dirtyWord, "****");
}
}
return value;
}
}
}
在web.xml文件中配置DirtyFilter:
<!--配置敏感字符過濾器-->
<filter>
<filter-name>DirtyFilter</filter-name>
<filter-class>di.cha.filter.DirtyFilter</filter-class>
<!-- 配置要過濾的敏感字符文件 -->
<init-param>
<param-name>dirtyWord</param-name>
<param-value>/WEB-INF/DirtyWord.txt</param-value>
</init-param>
</filter>
<filter-mapping>
<filter-name>DirtyFilter</filter-name>
<url-pattern>/*</url-pattern>
</filter-mapping>
當用戶填寫的內容包含一些敏感字符時,在DirtyFilter過濾器中就會將這些敏感字符替換掉。
我們如果將上述的CharacterEncodingFilter、HtmlFilter、DirtyFilter這三個過濾器聯合起來使用,那麼就相當於是把request對象包裝了3次,request對象的getParameter方法經過3次重寫,使得getParameter方法的功能大大增強,可以同時解決中文亂碼,html標籤轉義,敏感字符過濾這些需求。
在實際開發中完全可以將上述的三個過濾器合併成一個,讓合併後的過濾器具有解決中文亂碼,html標籤轉義,敏感字符過濾這些功能,例如:
import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStream;
import java.io.InputStreamReader;
import java.io.UnsupportedEncodingException;
import java.util.ArrayList;
import java.util.List;
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.http.HttpServletRequest;
import javax.servlet.http.HttpServletRequestWrapper;
import javax.servlet.http.HttpServletResponse;
/**
* @ClassName: AdvancedFilter
* @Description: 這個過濾器是用來解決中文亂碼,轉義內容中的html標籤,過濾內容中的敏感字符的
* @author: 孤傲蒼狼
* @date: 2014-9-6 下午6:17:37
*
*/
public class AdvancedFilter implements Filter {
private FilterConfig filterConfig = null;
//設置默認的字符編碼
private String defaultCharset = "UTF-8";
@Override
public void init(FilterConfig filterConfig) throws ServletException {
//得到過濾器的初始化配置信息
this.filterConfig = filterConfig;
}
@Override
public void doFilter(ServletRequest req, ServletResponse resp,
FilterChain chain) throws IOException, ServletException {
HttpServletRequest request = (HttpServletRequest) req;
HttpServletResponse response = (HttpServletResponse) resp;
//得到在web.xml中配置的字符編碼
String charset = filterConfig.getInitParameter("charset");
if(charset==null){
charset = defaultCharset;
}
request.setCharacterEncoding(charset);
response.setCharacterEncoding(charset);
response.setContentType("text/html;charset="+charset);
AdvancedRequest requestWrapper = new AdvancedRequest(request);
chain.doFilter(requestWrapper, response);
}
@Override
public void destroy() {
}
class AdvancedRequest extends HttpServletRequestWrapper{
private List<String> dirtyWords = getDirtyWords();
//定義一個變量記住被增強對象(request對象是需要被增強的對象)
private HttpServletRequest request;
//定義一個構造函數,接收被增強對象
public AdvancedRequest(HttpServletRequest request) {
super(request);
this.request = request;
}
/* 覆蓋需要增強的getParameter方法
* @see javax.servlet.ServletRequestWrapper#getParameter(java.lang.String)
*/
@Override
public String getParameter(String name) {
try{
//獲取參數的值
String value= this.request.getParameter(name);
if(value==null){
return null;
}
//如果不是以get方式提交數據的,就直接返回獲取到的值
if(!this.request.getMethod().equalsIgnoreCase("get")) {
//調用filter轉義value中的html標籤
value= filter(value);
}else{
//如果是以get方式提交數據的,就對獲取到的值進行轉碼處理
value = new String(value.getBytes("ISO8859-1"),this.request.getCharacterEncoding());
//調用filter轉義value中的html標籤
value= filter(value);
}
for(String dirtyWord : dirtyWords){
if(value.contains(dirtyWord)){
System.out.println("內容中包含敏感詞:"+dirtyWord+",將會被替換成****");
//替換敏感字符
value = value.replace(dirtyWord, "****");
}
}
return value;
}catch (Exception e) {
throw new RuntimeException(e);
}
}
}
/**
* @Method: filter
* @Description: 過濾內容中的html標籤
* @Anthor:孤傲蒼狼
* @param value
* @return
*/
public String filter(String value) {
if (value == null){
return null;
}
char content[] = new char[value.length()];
value.getChars(0, value.length(), content, 0);
StringBuffer result = new StringBuffer(content.length + 50);
for (int i = 0; i < content.length; i++) {
switch (content[i]) {
case '<':
result.append("<");
break;
case '>':
result.append(">");
break;
case '&':
result.append("&");
break;
case '"':
result.append(""");
break;
default:
result.append(content[i]);
}
}
return (result.toString());
}
/**
* @Method: getDirtyWords
* @Description: 獲取敏感字符
* @Anthor:孤傲蒼狼
*
* @return
*/
private List<String> getDirtyWords(){
List<String> dirtyWords = new ArrayList<String>();
String dirtyWordPath = filterConfig.getInitParameter("dirtyWord");
InputStream inputStream = filterConfig.getServletContext().getResourceAsStream(dirtyWordPath);
InputStreamReader is = null;
try {
is = new InputStreamReader(inputStream,defaultCharset);
} catch (UnsupportedEncodingException e2) {
e2.printStackTrace();
}
BufferedReader reader = new BufferedReader(is);
String line;
try {
while ((line = reader.readLine())!= null) {//如果 line爲空說明讀完了
dirtyWords.add(line);
}
} catch (IOException e) {
e.printStackTrace();
}
return dirtyWords;
}
}
在web.xml文件中配置AdvancedFilter:
<filter>
<filter-name>AdvancedFilter</filter-name>
<filter-class>di.cha.filter.AdvancedFilter</filter-class>
<init-param>
<param-name>charset</param-name>
<param-value>UTF-8</param-value>
</init-param>
<init-param>
<param-name>dirtyWord</param-name>
<param-value>/WEB-INF/DirtyWord.txt</param-value>
</init-param>
</filter>
<filter-mapping>
<filter-name>AdvancedFilter</filter-name>
<url-pattern>/*</url-pattern>
</filter-mapping>
AdvancedFilter過濾器同時具有解決中文亂碼,轉義內容中的html標籤,過濾內容中的敏感字符這些功能。
三、使用Decorator設計模式增強response對象
Servlet API 中提供了response對象的Decorator設計模式的默認實現類HttpServletResponseWrapper ,HttpServletResponseWrapper類實現了response接口中的所有方法,但這些方法的內部實現都是僅僅調用了一下所包裝的的 response對象的對應方法,以避免用戶在對response對象進行增強時需要實現response接口中的所有方法。
3.1、response增強案例——壓縮響應正文內容
應用HttpServletResponseWrapper對象,壓縮響應正文內容。
具體思路:通過filter向目標頁面傳遞一個自定義的response對象。在自定義的response對象中,重寫getOutputStream方法和getWriter方法,使目標資源調用此方法輸出頁面內容時,獲得的是我們自定義的ServletOutputStream對象。在我們自定義的ServletOuputStream對象中,重寫write方法,使寫出的數據寫出到一個buffer中。當頁面完成輸出後,在filter中就可得到頁面寫出的數據,從而我們可以調用GzipOuputStream對數據進行壓縮後再寫出給瀏覽器,以此完成響應正文件壓縮功能。
編寫壓縮過濾器,代碼如下:
import java.io.ByteArrayOutputStream;
import java.io.IOException;
import java.io.OutputStreamWriter;
import java.io.PrintWriter;
import java.util.zip.GZIPOutputStream;
import javax.servlet.Filter;
import javax.servlet.FilterChain;
import javax.servlet.FilterConfig;
import javax.servlet.ServletException;
import javax.servlet.ServletOutputStream;
import javax.servlet.ServletRequest;
import javax.servlet.ServletResponse;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import javax.servlet.http.HttpServletResponseWrapper;
/**
* @ClassName: GzipFilter
* @Description: 壓縮過濾器,將web應用中的文本都經過壓縮後再輸出到瀏覽器
* @author: 孤傲蒼狼
* @date: 2014-9-7 上午10:52:42
*
*/
public class GzipFilter implements Filter {
public void doFilter(ServletRequest req, ServletResponse resp,
FilterChain chain) throws IOException, ServletException {
HttpServletRequest request = (HttpServletRequest) req;
HttpServletResponse response = (HttpServletResponse) resp;
BufferResponse myresponse = new BufferResponse(response);
chain.doFilter(request, myresponse);
//拿出緩存中的數據,壓縮後再打給瀏覽器
byte out[] = myresponse.getBuffer();
System.out.println("原始大小:" + out.length);
ByteArrayOutputStream bout = new ByteArrayOutputStream();
//壓縮輸出流中的數據
GZIPOutputStream gout = new GZIPOutputStream(bout);
gout.write(out);
gout.close();
byte gzip[] = bout.toByteArray();
System.out.println("壓縮後的大小:" + gzip.length);
response.setHeader("content-encoding", "gzip");
response.setContentLength(gzip.length);
response.getOutputStream().write(gzip);
}
public void destroy() {
}
public void init(FilterConfig filterConfig) throws ServletException {
}
}
class BufferResponse extends HttpServletResponseWrapper{
private ByteArrayOutputStream bout = new ByteArrayOutputStream();
private PrintWriter pw;
private HttpServletResponse response;
public BufferResponse(HttpServletResponse response) {
super(response);
this.response = response;
}
@Override
public ServletOutputStream getOutputStream() throws IOException {
return new MyServletOutputStream(bout);
}
@Override
public PrintWriter getWriter() throws IOException {
pw = new PrintWriter(new OutputStreamWriter(bout,this.response.getCharacterEncoding()));
return pw;
}
public byte[] getBuffer(){
try{
if(pw!=null){
pw.close();
}
if(bout!=null){
bout.flush();
return bout.toByteArray();
}
return null;
}catch (Exception e) {
throw new RuntimeException(e);
}
}
}
class MyServletOutputStream extends ServletOutputStream{
private ByteArrayOutputStream bout;
public MyServletOutputStream(ByteArrayOutputStream bout){
this.bout = bout;
}
@Override
public void write(int b) throws IOException {
this.bout.write(b);
}
}
在web.xml中配置壓縮過濾器:
<filter>
<description>配置壓縮過濾器</description>
<filter-name>GzipFilter</filter-name>
<filter-class>di.cha.filter.GzipFilter</filter-class>
</filter>
<!--jsp文件的輸出的內容都經過壓縮過濾器壓縮後才輸出 -->
<filter-mapping>
<filter-name>GzipFilter</filter-name>
<url-pattern>*.jsp</url-pattern>
<!-- 配置過濾器的攔截方式-->
<!-- 對於在Servlet中通過
request.getRequestDispatcher("jsp頁面路徑").forward(request, response)
方式訪問的Jsp頁面的要進行攔截 -->
<dispatcher>FORWARD</dispatcher>
<!--對於直接以URL方式訪問的jsp頁面進行攔截,過濾器的攔截方式默認就是 REQUEST-->
<dispatcher>REQUEST</dispatcher>
</filter-mapping>
<!--js文件的輸出的內容都經過壓縮過濾器壓縮後才輸出 -->
<filter-mapping>
<filter-name>GzipFilter</filter-name>
<url-pattern>*.js</url-pattern>
</filter-mapping>
<!--css文件的輸出的內容都經過壓縮過濾器壓縮後才輸出 -->
<filter-mapping>
<filter-name>GzipFilter</filter-name>
<url-pattern>*.css</url-pattern>
</filter-mapping>
<!--html文件的輸出的內容都經過壓縮過濾器壓縮後才輸出 -->
<filter-mapping>
<filter-name>GzipFilter</filter-name>
<url-pattern>*.html</url-pattern>
</filter-mapping>
3.2、response增強案例——緩存數據到內存
對於頁面中很少更新的數據,例如商品分類,爲避免每次都要從數據庫查詢分類數據,因此可把分類數據緩存在內存或文件中,以此來減輕數據庫壓力,提高系統響應速度。
編寫緩存數據的過濾器,代碼如下:
import java.io.ByteArrayOutputStream;
import java.io.IOException;
import java.io.OutputStreamWriter;
import java.io.PrintWriter;
import java.util.HashMap;
import java.util.Map;
import javax.servlet.Filter;
import javax.servlet.FilterChain;
import javax.servlet.FilterConfig;
import javax.servlet.ServletException;
import javax.servlet.ServletOutputStream;
import javax.servlet.ServletRequest;
import javax.servlet.ServletResponse;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import javax.servlet.http.HttpServletResponseWrapper;
/**
* @ClassName: WebResourceCachedFilter
* @Description: Web資源緩存過濾器
* @author: 孤傲蒼狼
* @date: 2014-9-8 上午12:20:16
*
*/
public class WebResourceCachedFilter implements Filter {
/**
* @Field: map
* 緩存Web資源的Map容器
*/
private Map<String,byte[]> map = new HashMap<String,byte[]>();
@Override
public void init(FilterConfig filterConfig) throws ServletException {
}
@Override
public void doFilter(ServletRequest req, ServletResponse resp,
FilterChain chain) throws IOException, ServletException {
HttpServletRequest request = (HttpServletRequest) req;
HttpServletResponse response = (HttpServletResponse) resp;
//1.得到用戶請求的uri
String uri = request.getRequestURI();
//2.看緩存中有沒有uri對應的數據
byte b[] = map.get(uri);
//3.如果緩存中有,直接拿緩存的數據打給瀏覽器,程序返回
if(b!=null){
//根據字節數組和指定的字符編碼構建字符串
String webResourceHtmlStr = new String(b,response.getCharacterEncoding());
System.out.println(webResourceHtmlStr);
response.getOutputStream().write(b);
return;
}
//4.如果緩存沒有,讓目標資源執行,並捕獲目標資源的輸出
BufferResponse myresponse = new BufferResponse(response);
chain.doFilter(request, myresponse);
//獲取緩衝流中的內容的字節數組
byte out[] = myresponse.getBuffer();
//5.把資源的數據以用戶請求的uri爲關鍵字保存到緩存中
map.put(uri, out);
//6.把數據打給瀏覽器
response.getOutputStream().write(out);
}
@Override
public void destroy() {
}
class BufferResponse extends HttpServletResponseWrapper{
private ByteArrayOutputStream bout = new ByteArrayOutputStream(); //捕獲輸出的緩存
private PrintWriter pw;
private HttpServletResponse response;
public BufferResponse(HttpServletResponse response) {
super(response);
this.response = response;
}
@Override
public ServletOutputStream getOutputStream() throws IOException {
return new MyServletOutputStream(bout);
}
@Override
public PrintWriter getWriter() throws IOException {
pw = new PrintWriter(new OutputStreamWriter(bout,this.response.getCharacterEncoding()));
return pw;
}
public byte[] getBuffer(){
try{
if(pw!=null){
pw.close();
}
return bout.toByteArray();
}catch (Exception e) {
throw new RuntimeException(e);
}
}
}
class MyServletOutputStream extends ServletOutputStream{
private ByteArrayOutputStream bout;
public MyServletOutputStream(ByteArrayOutputStream bout){ //接收數據寫到哪裏
this.bout = bout;
}
@Override
public void write(int b) throws IOException {
bout.write(b);
}
}
}
<filter>
<description>Web資源緩存過濾器</description>
<filter-name>WebResourceCachedFilter</filter-name>
<filter-class>di.cha.filter.WebResourceCachedFilter</filter-class>
</filter>
<filter-mapping>
<filter-name>WebResourceCachedFilter</filter-name>
<!-- 映射需要緩存輸出的JSP頁面,這幾個頁面都只是單純作爲輸入UI,不會有太多的變化,因此可以緩存輸出 -->
<url-pattern>/login.jsp</url-pattern>
<url-pattern>/test.jsp</url-pattern>
<url-pattern>/test2.jsp</url-pattern>
</filter-mapping>