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?package?com.techsboy.filter; 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.annotation.WebFilter; import?javax.servlet.http.HttpServletRequest; import?javax.servlet.http.HttpServletResponse; import?javax.servlet.http.HttpServletResponseWrapper;/** *?tip:?PrintWriter，ServletOutputStream，JspWriter的輸出過程*?response對(duì)象getOutputSteam()和getWriter()方法分別獲得ServletOutputStream?out*?和PrintWriter?writer輸出對(duì)象，out.write(..),out.print(..)和out.println(..)方法*?最終都要使用out的write(int?b)方法來輸出數(shù)據(jù)。writer.write(..),writer.print(..),*?writer.println(..)方法可以自定義指定的流（通過PrintWriter的構(gòu)造方法注入指定的流）*?來將字符流轉(zhuǎn)換成字節(jié)流輸出。JspWriter的輸出最終是輸出到PrintWriter的緩存的前面， *?（因此總是優(yōu)先輸出PrintWriter的數(shù)據(jù)，在輸出JspWriter的數(shù)據(jù)，除非調(diào)用flush()），*?因此在調(diào)用JspWriter輸出前會(huì)使用response獲得PrintWriter對(duì)象，將數(shù)據(jù)輸出到該對(duì)象*?指定的緩存中，然后再用PrintWriter對(duì)象輸出客戶端。*?由上可見，解決全站壓縮問題要把住前兩個(gè)輸出對(duì)象的最后輸出關(guān)口，在關(guān)口處獲得數(shù)據(jù)*?壓縮處理，然后在把壓縮后的數(shù)據(jù)輸出。（注意?struts2會(huì)獲取兩次PrintWriter對(duì)象）*?全站壓縮過濾器類，負(fù)責(zé)將所有輸出都經(jīng)過壓縮后反饋給客戶端*/ @WebFilter("/*") public?class?GZIPCompressFilter?implements?Filter?{/***?@see?Filter#doFilter(ServletRequest,?ServletResponse,?FilterChain)*/public?void?doFilter(ServletRequest?req,?ServletResponse?resp,?FilterChain?chain)?throws?IOException,?ServletException?{HttpServletRequest?request?=?(HttpServletRequest)req;HttpServletResponse?response?=?(HttpServletResponse)resp;//在壓縮前對(duì)response方法進(jìn)行改寫，采用繼承包裝類的方法實(shí)現(xiàn)MyHttpServletResponse?myResponse?=?new?MyHttpServletResponse(response);chain.doFilter(request,?myResponse);//提取源數(shù)據(jù)進(jìn)行壓縮，使用源輸出流輸出//獲取源數(shù)據(jù)byte[]?b?=?myResponse.getSourceData();if(b.length!=0){//帶緩存的字節(jié)數(shù)組輸出流，存放壓縮后的數(shù)據(jù)ByteArrayOutputStream?byteOut?=?new?ByteArrayOutputStream();//對(duì)源數(shù)據(jù)進(jìn)行壓縮GZIPOutputStream?gzip?=?new?GZIPOutputStream(byteOut);gzip.write(b);gzip.close();//將壓縮的數(shù)據(jù)輸出給客戶端，同時(shí)通知客戶端解壓縮格式和內(nèi)容長(zhǎng)度byteOut.flush();b?=?byteOut.toByteArray();response.setHeader("Content-Encoding",?"gzip");response.setContentLength(b.length);response.getOutputStream().write(b);}}/***?@see?Filter#init(FilterConfig)*/public?void?init(FilterConfig?fConfig)?throws?ServletException?{}@Overridepublic?void?destroy()?{} }/***?自定義類繼承HttpServletResponse包裝類，改寫父類response獲得輸出流的兩個(gè)方法，從而*?實(shí)現(xiàn)所有輸出的數(shù)據(jù)被指定到一個(gè)帶緩存的字節(jié)數(shù)組輸出流中，以便可以方便的獲得輸出的*?源數(shù)據(jù)，來進(jìn)行壓縮操作。*/ class?MyHttpServletResponse?extends?HttpServletResponseWrapper?{private?ByteArrayOutputStream?byteOut?=?new?ByteArrayOutputStream();private?PrintWriter?writer?=?null;public?MyHttpServletResponse(HttpServletResponse?response)?{super(response);}/***?改寫父類的方法，創(chuàng)建一個(gè)類繼承ServletOutputStream（并注入一個(gè)帶緩存的字節(jié)數(shù)組輸出流對(duì)象），*?該類改寫父類的write(int?b)方法，使得使用該類對(duì)象的方法輸出的數(shù)據(jù)都將輸出到字節(jié)數(shù)組輸出流的*?緩存中?*/@Overridepublic?ServletOutputStream?getOutputStream()?throws?IOException?{MyServletOutputStream?myOut?=?new?MyServletOutputStream(byteOut);return?myOut;}/***?改寫父類的方法，返回一個(gè)帶自己設(shè)定輸出流的PrintWriter對(duì)象*/@Overridepublic?PrintWriter?getWriter()?throws?IOException?{//?這是錯(cuò)的，該輸出流將字符流轉(zhuǎn)換成字節(jié)流使用的是平臺(tái)默認(rèn)字符集編碼ISO-8859-1 //??PrintWriter?writer?=?new?PrintWriter(byteOut);//下面才是正解,不過要注意判斷writer是否已經(jīng)被創(chuàng)建過，創(chuàng)建過就不要再創(chuàng)建了， //否則第一個(gè)writer的內(nèi)容就得不到輸出。 //struts2就是這種情形，他會(huì)調(diào)用該方法兩次生成兩次writerif(writer==null)writer?=?new?PrintWriter(new?OutputStreamWriter(byteOut,super.getCharacterEncoding()),true);return?writer;}/***?獲取源數(shù)據(jù)的字節(jié)數(shù)組*?@return?源數(shù)據(jù)的一個(gè)字節(jié)數(shù)組*/public?byte[]?getSourceData(){try?{if(writer!=null){writer.close();}byteOut.flush();}?catch?(IOException?e)?{throw?new?RuntimeException(e);}return?byteOut.toByteArray();} }/***?實(shí)現(xiàn)ServletOutputStream的輸出流（注入一個(gè)帶緩存的字節(jié)數(shù)組輸出流），*?改寫了父類的write(int?b)方法，實(shí)現(xiàn)該輸出流輸出數(shù)據(jù)統(tǒng)一指定到字節(jié)數(shù)組輸出流緩存中。*/ class?MyServletOutputStream?extends?ServletOutputStream{private?ByteArrayOutputStream?byteOut;public?MyServletOutputStream(ByteArrayOutputStream?byteOut){this.byteOut?=?byteOut;}@Overridepublic?void?write(int?b)?throws?IOException?{byteOut.write(b);} }

轉(zhuǎn)載于:https://my.oschina.net/techsboy/blog/221988

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