关于过滤器的一个例子（涉及到装饰模式）

全站压缩问题的GZIP过滤器实现

最新推荐文章于 2025-08-19 20:43:24 发布

原创最新推荐文章于 2025-08-19 20:43:24 发布 · 662 阅读

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本文介绍了一个解决全站压缩问题的GZIP过滤器实现过程，包括类继承、构造函数定义、方法覆盖及GZIP压缩操作。

Decorator设计模式的实现

•1.首先看需要被增强对象继承了什么接口或父类，编写一个类也去继承这些接口或父类。

•2.在类中定义一个变量，变量类型即需增强对象的类型。

•3.在类中定义一个构造函数，接收需增强的对象。

•4.覆盖需增强的方法，编写增强的代码。

下面是一个解决全站压缩问题的一个过滤器，关于过滤器的执行过程我就不多说了。

package com.why.web.filter;

import java.io.ByteArrayOutputStream;
import java.io.IOException;
import java.io.OutputStream;
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;

import com.sun.org.apache.bcel.internal.generic.NEW;


//解决全站压缩问题
public class GzipFilter implements Filter {

	public void init(FilterConfig filterConfig) throws ServletException {
		

	}

	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);
		
		
		//拿出缓存中的数据，压缩后再打给浏览器
		byte[] bytes = myresponse.getBuffer();
		
		ByteArrayOutputStream bout = new ByteArrayOutputStream();
		GZIPOutputStream gzip = new GZIPOutputStream(bout);
		gzip.write(bytes);
		gzip.close();
		
		
		
		byte[] gzipbyte = bout.toByteArray();
		
		
		response.setHeader("content-encoding", "gzip");
		response.setContentLength(gzipbyte.length);
		response.getOutputStream().write(gzipbyte);
		
	}

	public void destroy() {
		

	}
}

class BufferResponse extends HttpServletResponseWrapper{
	
	private HttpServletResponse response;
	private ByteArrayOutputStream bout = new ByteArrayOutputStream();
	private PrintWriter pw;

	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,response.getCharacterEncoding()));
		//pw = new PrintWriter(bout);
		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) {
		super();
		this.bout = bout;
	}

	@Override
	public void write(int b) throws IOException {
		
		this.bout.write(b);
		
	}
	
}