过滤器Filter也具有生命周期：init()-doFilter()-destroy()，由部署文件中的filter元素驱动。在servlet2.4中，过滤器异样可以用于恳求分派器，但须在web.xml中声明，dispatcherINCLUDE或FORWARD或REQUEST或ERROR/dispatcher该元素位于filter-mapping中。
一、批量设置恳求编码
Java代码 public class EncodingFilter implements Filter { private String encoding = null; public void destroy() { encoding = null; } public void doFilter(ServletRequest request, ServletResponse response, FilterChain chain) throws IOException, ServletException { String encoding = getEncoding(); if (encoding == null){ encoding = "gb2312"; } request.setCharacterEncoding(encoding);// 在恳求里设置上指定的编码 chain.doFilter(request, response); } public void init(FilterConfig filterConfig) throws ServletException { this.encoding = filterConfig.getInitParameter("encoding"); } private String getEncoding() { return this.encoding; } }
public class EncodingFilter implements Filter {
private String encoding = null;
public void destroy() {encoding = null;}
public void doFilter(ServletRequest request, ServletResponse response,FilterChain chain) throws IOException, ServletException {String encoding = getEncoding();if (encoding == null){encoding = "gb2312";}request.setCharacterEncoding(encoding);// 在恳求里设置上指定的编码chain.doFilter(request, response);}
public void init(FilterConfig filterConfig) throws ServletException {this.encoding = filterConfig.getInitParameter("encoding");}
private String getEncoding() {return this.encoding;}
}
Xml代码 filter filter-nameEncodingFilter/filter-name filter-classcom.logcd.filter.EncodingFilter/filter-class init-param param-nameencoding/param-name param-valuegb2312/param-value /init-param /filter filter-mapping filter-nameEncodingFilter/filter-name url-pattern/*/url-pattern /filter-mapping
filter filter-nameEncodingFilter/filter-name filter-classcom.logcd.filter.EncodingFilter/filter-class init-param param-nameencoding/param-name param-valuegb2312/param-value /init-param/filter
filter-mapping filter-nameEncodingFilter/filter-name url-pattern/*/url-pattern/filter-mapping
二、用filter控制用户拜访权限
Java代码 public void doFilter(ServletRequest request, ServletResponse response, FilterChain chain) throws IOException, ServletException { HttpServletRequest req = (HttpServletRequest) request; HttpServletResponse res = (HttpServletResponse) response; HttpSession session = req.getSession(); if (session.getAttribute("username") != null) {//登录后才能拜访 chain.doFilter(request, response); } else { res.sendRedirect("../failure.jsp"); } }
public void doFilter(ServletRequest request, ServletResponse response, FilterChain chain) throws IOException, ServletException {
HttpServletRequest req = (HttpServletRequest) request; HttpServletResponse res = (HttpServletResponse) response;
HttpSession session = req.getSession(); if (session.getAttribute("username") != null) {//登录后才能拜访 chain.doFilter(request, response); } else { res.sendRedirect("../failure.jsp"); }}
Xml代码 filter filter-nameSecurityFilter/filter-name filter-classcom.logcd.filter.SecurityFilter/filter-class /filter filter-mapping filter-nameSecurityFilter/filter-name url-pattern/admin/*/url-pattern /filter-mapping
filter filter-nameSecurityFilter/filter-name filter-classcom.logcd.filter.SecurityFilter/filter-class/filterfilter-mapping filter-nameSecurityFilter/filter-name url-pattern/admin/*/url-pattern/filter-mapping
三、过滤链 两个过滤器，EncodingFilter担任设置编码，SecurityFilter担任控制权限，服务器会按照web.xml中过滤器定义的先后循序组装成一条链，然后一次执行其中的doFilter()方法。执行的顺序就如上图所示，执行第一个过滤器的chain.doFilter()之前的代码，第二个过滤器的chain.doFilter()之前的代码，恳求的资源，第二个过滤器的chain.doFilter()之后的代码，第一个过滤器的chain.doFilter()之后的代码，最后前往响应。 执行的代码顺序是：
执行EncodingFilter.doFilter()中chain.doFilter()之前的部分：request.setCharacterEncoding("gb2312"); 执行SecurityFilter.doFilter()中chain.doFilter()之前的部分：判断用户是否已登录。 假如用户已登录，则拜访恳求的资源：/admin/index.jsp。 假如用户未登录，则页面重定向到：/failure.jsp。 执行SecurityFilter.doFilter()中chain.doFilter()之后的部分：这里没有代码。 执行EncodingFilter.doFilter()中chain.doFilter()之后的部分：这里也没有代码。
过滤链的益处是，执行进程中任何时候都可以打断，只需不执行chain.doFilter()就不会再执行前面的过滤器和恳求的内容。而在实际使用时，就要特别留意过滤链的执行顺序问题，像EncodingFilter就一定要放在一切Filter之前，这样才能确保在使用恳求中的数据前设置正确的编码。
四、使用filter,结合gzip 压缩技术,解决web使用中网络传输数据量大的问题 gzip是http协议中使用的一种加密算法,客户端向web服务器端发出了恳求后，通常情况下服务器端会将页面文件和其他资源，前往到客户端，客户端加载后渲染呈现，这种情况文件普通都比较大，假如开启Gzip ，那么服务器端响应后，会将页面，JS,CSS等文本文件或许其他文件经过高压缩算法将其压缩，然后传输到客户端，由客户端的阅读器担任解压缩与呈现。通常能节省40%以上的流量（普通都有60%左右），一些PHP，JSP文件也能够停止压缩。 1.Tomcat 直接开启Gzip 打开Tomcat 目录下的conf下的server.xml，并找到如下信息: Xml代码 !-- Note : To use gzip compression you could set the following properties : compression="on" compressionMinSize="2048" noCompressionUserAgents="gozilla, traviata" compressableMimeType="text/html,text/xml" --
!-- Note : To use gzip compression you could set the following properties : compression="on" compressionMinSize="2048" noCompressionUserAgents="gozilla, traviata" compressableMimeType="text/html,text/xml"--
把它们加入到你配置的Connector port="80" .../中去。假如要压缩css 和 js，加入compressableMimeType="text/html,text/xml,text/css,text/javascript"。还要压缩图片,加入compressableMimeType="text/html,text/xml,text/css,text/javascript,image/gif,image/jpg"。 开启后重启Tomcat ，经过阅读器查看headers信息就能看到是否开启。
2.使用filter,在代码级别完成web使用的gzip压缩的开启。
(1).CachedResponseWrapper类 实现定制输入的关键是对HttpServletResponse 停止包装，截获一切的输入，等到过滤器链处理终了后，再对截获的输入停止处理，并写入到真正的HttpServletResponse 对象中。JavaEE 框架已经定义了一个HttpServletResponseWrapper 类使得包装HttpServletResponse 愈加容易。我们扩展这个HttpServletResponseWrapper，截获一切的输入，并保管到ByteArrayOutputStream 中。 定制的包装响应能方便地从帮助类 HttpServletResponseWrapper 中导出。这一类粗略地执行许多方法，允许我们简单地覆盖 getOutputStream() 方法以及 getWriter() 方法，提供了定制输入流的实例。 HttpServletResponseWrapper这个类的使用包括以下五个步骤： 1）建立一个响应包装器。扩展javax.servlet.http.HttpServletResponseWrapper。 2）提供一个缓存输入的PrintWriter。重载getWriter方法，前往一个保管发送给它的一切东西的PrintWriter，并把结果存进一个可以稍后拜访的字段中。 3）传递该包装器给doFilter。此调用是合法的，因为HttpServletResponseWrapper实现HttpServletResponse。 4）提取和修正输入。在调用FilterChain的doFilter方法后，原资源的输入只需应用步骤2中提供的机制就可以得到。只需对你的使用适宜，就可以修正或替换它。 5）发送修正过的输入到客户机。因为原资源不再发送输入到客户机（这些输入已经寄存到你的响应包装器中了），所以必需发送这些输入。这样，你的过滤器需求从原响应对象中获得PrintWriter或OutputStream，并传递修正过的输入到该流中。 Java代码 /** * Wrapper:在内存中开拓一个ByteOutputStream，然后将阻拦的响应写入byte[]， * 写入终了后，再将wrapper的byte[]写入真正的response对象 * This class is used for wrapped response for getting cached data. */ class CachedResponseWrapper extends HttpServletResponseWrapper { /** * Indicate that getOutputStream() or getWriter() is not called yet. */ public static final int OUTPUT_NONE = 0; /** * Indicate that getWriter() is already called. */ public static final int OUTPUT_WRITER = 1; /** * Indicate that getOutputStream() is already called. */ public static final int OUTPUT_STREAM = 2; private int outputType = OUTPUT_NONE; private int status = SC_OK; private ServletOutputStream output = null; private PrintWriter writer = null; private ByteArrayOutputStream buffer = null; public CachedResponseWrapper(HttpServletResponse resp) throws IOException { super(resp); buffer = new ByteArrayOutputStream(); } public int getStatus() { return status; } public void setStatus(int status) { super.setStatus(status); this.status = status; } public void setStatus(int status, String string) { super.setStatus(status, string); this.status = status; } public void sendError(int status, String string) throws IOException { super.sendError(status, string); this.status = status; } public void sendError(int status) throws IOException { super.sendError(status); this.status = status; } public void sendRedirect(String location) throws IOException { super.sendRedirect(location); this.status = SC_MOVED_TEMPORARILY; } public PrintWriter getWriter() throws IOException { if (outputType == OUTPUT_STREAM) throw new IllegalStateException(); else if (outputType == OUTPUT_WRITER) return writer; else { outputType = OUTPUT_WRITER; writer = new PrintWriter(new OutputStreamWriter(buffer, getCharacterEncoding())); return writer; } } public ServletOutputStream getOutputStream() throws IOException { if (outputType == OUTPUT_WRITER) throw new IllegalStateException(); else if (outputType == OUTPUT_STREAM) return output; else { outputType = OUTPUT_STREAM; output = new WrappedOutputStream(buffer); return output; } } public void flushBuffer() throws IOException { if (outputType == OUTPUT_WRITER) writer.flush(); if (outputType == OUTPUT_STREAM) output.flush(); } public void reset() { outputType = OUTPUT_NONE; buffer.reset(); } /** * Call this method to get cached response data. * * @return byte array buffer. * @throws IOException */ public byte[] getResponseData() throws IOException { flushBuffer(); return buffer.toByteArray(); } /** * This class is used to wrap a ServletOutputStream and store output stream * in byte[] buffer. */ class WrappedOutputStream extends ServletOutputStream { private ByteArrayOutputStream buffer; public WrappedOutputStream(ByteArrayOutputStream buffer) { this.buffer = buffer; } public void write(int b) throws IOException { buffer.write(b); } public byte[] toByteArray() { return buffer.toByteArray(); } } }
/*** Wrapper:在内存中开拓一个ByteOutputStream，然后将阻拦的响应写入byte[]，* 写入终了后，再将wrapper的byte[]写入真正的response对象* This class is used for wrapped response for getting cached data.*/ class CachedResponseWrapper extends HttpServletResponseWrapper {
/** * Indicate that getOutputStream() or getWriter() is not called yet. */public static final int OUTPUT_NONE = 0;
/** * Indicate that getWriter() is already called. */public static final int OUTPUT_WRITER = 1;
/** * Indicate that getOutputStream() is already called. */public static final int OUTPUT_STREAM = 2;
private int outputType = OUTPUT_NONE;
private int status = SC_OK;
private ServletOutputStream output = null;
private PrintWriter writer = null;
private ByteArrayOutputStream buffer = null;
public CachedResponseWrapper(HttpServletResponse resp) throws IOException {super(resp);buffer = new ByteArrayOutputStream();}
public int getStatus() {return status;}
public void setStatus(int status) {super.setStatus(status);this.status = status;}
public void setStatus(int status, String string) {super.setStatus(status, string);this.status = status;}
public void sendError(int status, String string) throws IOException {super.sendError(status, string);this.status = status;}
public void sendError(int status) throws IOException {super.sendError(status);this.status = status;}
public void sendRedirect(String location) throws IOException {super.sendRedirect(location);this.status = SC_MOVED_TEMPORARILY;}
public PrintWriter getWriter() throws IOException {if (outputType == OUTPUT_STREAM)throw new IllegalStateException();else if (outputType == OUTPUT_WRITER)return writer;else {outputType = OUTPUT_WRITER;writer = new PrintWriter(new OutputStreamWriter(buffer,getCharacterEncoding()));return writer;}}
public ServletOutputStream getOutputStream() throws IOException {if (outputType == OUTPUT_WRITER)throw new IllegalStateException();else if (outputType == OUTPUT_STREAM)return output;else {outputType = OUTPUT_STREAM;output = new WrappedOutputStream(buffer);return output;}}
public void flushBuffer() throws IOException {if (outputType == OUTPUT_WRITER)writer.flush();if (outputType == OUTPUT_STREAM)output.flush();}
public void reset() {outputType = OUTPUT_NONE;buffer.reset();}
/** * Call this method to get cached response data. * * @return byte array buffer. * @throws IOException */public byte[] getResponseData() throws IOException {flushBuffer();return buffer.toByteArray();}
/** * This class is used to wrap a ServletOutputStream and store output stream * in byte[] buffer. */class WrappedOutputStream extends ServletOutputStream {
private ByteArrayOutputStream buffer;
public WrappedOutputStream(ByteArrayOutputStream buffer) {this.buffer = buffer;}
public void write(int b) throws IOException {buffer.write(b);}
public byte[] toByteArray() {return buffer.toByteArray();}}
}
(2).GZipFilter类 Java代码 public class GZipFilter implements Filter { public void init(FilterConfig arg0) throws ServletException { } public void doFilter(ServletRequest request, ServletResponse response, FilterChain chain) throws IOException, ServletException { HttpServletResponse httpResponse = (HttpServletResponse) response; CachedResponseWrapper wrapper = new CachedResponseWrapper(httpResponse); // 写入wrapper: chain.doFilter(request, wrapper); // 对响应停止处理，这里是停止GZip压缩: byte[] data = GZipUtil.gzip(wrapper.getResponseData()); httpResponse.setHeader("Content-Encoding", "gzip"); httpResponse.setContentLength(data.length); ServletOutputStream output = response.getOutputStream(); output.write(data); output.flush(); } public void destroy() { } }
public class GZipFilter implements Filter {public void init(FilterConfig arg0) throws ServletException {}
public void doFilter(ServletRequest request, ServletResponse response,FilterChain chain) throws IOException, ServletException {
HttpServletResponse httpResponse = (HttpServletResponse) response;CachedResponseWrapper wrapper = new CachedResponseWrapper(httpResponse);// 写入wrapper:chain.doFilter(request, wrapper);// 对响应停止处理，这里是停止GZip压缩:byte[] data = GZipUtil.gzip(wrapper.getResponseData());httpResponse.setHeader("Content-Encoding", "gzip");httpResponse.setContentLength(data.length);ServletOutputStream output = response.getOutputStream();output.write(data);output.flush();}
public void destroy() {
}
}
(3).GZipUtil类 Java代码 public final class GZipUtil { /** * Do a gzip operation. */ public static byte[] gzip(byte[] data) { ByteArrayOutputStream byteOutput = new ByteArrayOutputStream(10240); GZIPOutputStream output = null; try { output = new GZIPOutputStream(byteOutput); output.write(data); } catch (IOException e) { throw new RuntimeException("G-Zip failed.", e); } finally { if (output != null) { try { output.close(); } catch (IOException e) { } } } return byteOutput.toByteArray(); } }
public final class GZipUtil {/** * Do a gzip operation. */public static byte[] gzip(byte[] data) {ByteArrayOutputStream byteOutput = new ByteArrayOutputStream(10240);GZIPOutputStream output = null;try {output = new GZIPOutputStream(byteOutput);output.write(data);} catch (IOException e) {throw new RuntimeException("G-Zip failed.", e);} finally {if (output != null) {try {output.close();} catch (IOException e) {}}}return byteOutput.toByteArray();}}
(4).在web.xml中配置 GZipFilter Xml代码 filter filter-nameGZipFilter/filter-name filter-classcom.logcd.filter.GZipFilter/filter-class /filter filter-mapping filter-nameGZipFilter/filter-name url-pattern*.html/url-pattern /filter-mapping
filter filter-nameGZipFilter/filter-name filter-classcom.logcd.filter.GZipFilter/filter-class /filter filter-mapping filter-nameGZipFilter/filter-name url-pattern*.html/url-pattern /filter-mapping
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斐格整理，收集辛苦，希望能保留出处，谢谢斑竹大哥。
