javaweb之压缩过滤器

过滤器是提高网站性能的必须之物 下面就是一个过滤器的简单demon

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.HttpServletRequestWrapper;
import javax.servlet.http.HttpServletResponse;
import javax.servlet.http.HttpServletResponseWrapper;

public class GzipFilter implements Filter {

@Override
public void destroy() {
// TODO Auto-generated method stub

}

@Override
public void doFilter(ServletRequest req, ServletResponse resp,
FilterChain chain) throws IOException, ServletException {
// TODO Auto-generated method stub
HttpServletRequest request = (HttpServletRequest) req;
HttpServletResponse response = (HttpServletResponse) resp;
//response.getOutputStream().writer   respnose.getWriter().writer();
//定义自己的增强版 response
Myresponse myresponse = new Myresponse(response);
chain.doFilter(request, myresponse);

byte[] bout= myresponse.getBuffer();
System.out.println("压之前"+bout.length);
byte[] gzipb = gzip(bout);
System.out.println("压之后"+gzipb.length);

//原理相当与 原本由普通的response 直接输出给了浏览器 但被我增强一把之后 数据就被我截获了
//保存在我的那个 byteArrayOutputStream 中了 然后我取出来处理了下 不过最后还是要物归原主 返回给浏览器
response.setHeader("content-encoding", "gzip");
response.setHeader("content-length", gzipb.length+"");
response.getOutputStream().write(gzipb);

}

public byte[] gzip(byte[] bout){

ByteArrayOutputStream out= new ByteArrayOutputStream();
try{
GZIPOutputStream gzipout= new GZIPOutputStream(out);
gzipout.write(bout);
gzipout.close();		//因为GZIPOutputStream是缓冲流
return out.toByteArray();
}catch (Exception e) {
// TODO: handle exception
throw new RuntimeException(e);
}

}

class Myresponse extends HttpServletResponseWrapper{
private ByteArrayOutputStream bout= new ByteArrayOutputStream();
private HttpServletResponse response;
private PrintWriter pw;
public Myresponse(HttpServletResponse response) {
super(response);
// TODO Auto-generated constructor stub
this.response = response;
}
@Override
public ServletOutputStream getOutputStream() throws IOException {
// TODO Auto-generated method stub
//看返回类型  得知 它是个抽象类 所以没办法治好自己实现它了 然后再将数据写到定义到到的那个流中

return  new MyServletOutputStream(bout) ;
}

@Override
public PrintWriter getWriter() throws IOException {
// TODO Auto-generated method stub
// PrintWriter(OutputStream out) 虽然有这个方法 但是并不能指定码表编码所以容易造成乱码
//必须用一个能支持编码的流作为传递的依赖 所以才有了以下这个写法
pw = new PrintWriter(new OutputStreamWriter(bout,"utf-8"));
return pw;
}
public byte[] getBuffer(){
if(pw !=null){
pw.close();	//因为 PrintWriter 是个包装流 所以也要关闭
}
return bout.toByteArray();
}
}

class MyServletOutputStream extends ServletOutputStream{
private ByteArrayOutputStream bout= new ByteArrayOutputStream();

public MyServletOutputStream(ByteArrayOutputStream bout) {
// TODO Auto-generated constructor stub
this.bout = bout;
}
@Override
public void write(int b) throws IOException {
// TODO Auto-generated method stub

//每个字有自己的字节码 比如 a 的ascii码为97
bout.write(b);

}

}

@Override
public void init(FilterConfig filterConfig) throws ServletException {
// TODO Auto-generated method stub

}

}

当然写完这些之后这个过滤肯定是不能用的 我们必须还要去web.xml中配置 配置的时候还是有个小细节需要捋捋

<filter>
<filter-name>gzipFilter</filter-name>
<filter-class>com.tb.bookshoop.web.Filter.GzipFilter
</filter-class>
</filter>
<filter-mapping>
<filter-name>gzipFilter</filter-name>
<url-pattern>*.jsp</url-pattern>
<dispatcher>FORWARD</dispatcher>
<dispatcher>REQUEST</dispatcher>
</filter-mapping>

<filter-mapping>
<filter-name>gzipFilter</filter-name>
<url-pattern>*.html</url-pattern>
<dispatcher>FORWARD</dispatcher>
<dispatcher>REQUEST</dispatcher>
</filter-mapping>

<filter-mapping>
<filter-name>gzipFilter</filter-name>
<url-pattern>*.css</url-pattern>
<dispatcher>FORWARD</dispatcher>
<dispatcher>REQUEST</dispatcher>
</filter-mapping>

<filter-mapping>
<filter-name>gzipFilter</filter-name>
<url-pattern>*.js</url-pattern>
<dispatcher>FORWARD</dispatcher>
<dispatcher>REQUEST</dispatcher>
</filter-mapping>

首先 gzip是对文本有比较高的压缩率 所以路径就配了 jsp html css js 的了 其次 由于在服务器内部 我们访问这些资源的时候可能是采取转发的形式来访问 所以dispatcher必须也要配上FORWORD 这样一个简单的压缩过滤器就做好了 下面是测试额压缩率