Filter 常用代码

1. 压缩 Filter

// GZIPFilter.java

package org.demo.filter;

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.HttpServletResponse;
/**
 * Filter that compress output with gzip.
 * Code from http://www.onjava.com/pub/a/onjava/2003/11/19/filters.html
 * @author dycc
 *
 */
public class GZIPFilter implements Filter{
	@Override
	public void init(FilterConfig arg0) throws ServletException {
		// No operation.
	}
	
	@Override
	public void doFilter(ServletRequest req, ServletResponse resp,
			FilterChain chain) throws IOException, ServletException {
		if (req instanceof HttpServletRequest){
			HttpServletRequest request = (HttpServletRequest)req;
			HttpServletResponse response = (HttpServletResponse)resp;
			// check for gzip capability
			String ac = request.getHeader("accept-encoding");
			if (ac == null || ac.indexOf("gzip") == -1){
				// not support gzip.
				chain.doFilter(request, response);				
			} else {
			    // support gzip.
				GZIPResponseWrapper wrappedResp = new GZIPResponseWrapper(response);
				chain.doFilter(request, wrappedResp);
				wrappedResp.finish();
			}
		}
		
	}
	
	@Override
	public void destroy() {
		// No operation.
	}
}

 

// GZIPResponseWrapper.java

package org.demo.filter;

import java.io.IOException;
import java.io.OutputStreamWriter;
import java.io.PrintWriter;

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

/**
 * Wrap for GZIPFilter
 * @author dycc
 *
 */
public class GZIPResponseWrapper extends HttpServletResponseWrapper{
	protected HttpServletResponse original_resp = null;
	protected ServletOutputStream stream = null;
	protected PrintWriter writer = null;
	
	public GZIPResponseWrapper(HttpServletResponse response) {
		super(response);
		this.original_resp = response;
	}
	
	@Override
	public ServletOutputStream getOutputStream() throws IOException {
		if (writer != null){
			throw new IllegalStateException("getWriter() has already been called.");
		}
		if (stream == null){
			stream = new GZIPResponseStream(original_resp);
		}
		return stream;
	}
	
	@Override
	public PrintWriter getWriter() throws IOException {
		if (stream != null){
			throw new IllegalStateException("getOutputStream() has already been called.");
		}
		if (writer == null){
			writer = new PrintWriter(
					   new OutputStreamWriter(
				         new GZIPResponseStream(original_resp),"UTF-8"));
		}
		return writer;
	}
	
	@Override
	public void flushBuffer() throws IOException {
		if (stream != null){
			stream.flush();
		} else if (writer != null){
		    writer.flush();
		}
	}
	
	public void finish(){
		try {
			if (stream != null){
				stream.close();
			} else if (writer != null){
				writer.close();
			}
		} catch (IOException e){
			// Ignore.
		}
	}
}

 

 

// GZIPResponseStream.java

package org.demo.filter;

import java.io.ByteArrayOutputStream;
import java.io.IOException;
import java.util.zip.GZIPOutputStream;

import javax.servlet.ServletOutputStream;
import javax.servlet.http.HttpServletResponse;

/**
 * Wrap response stream for GZIPFilter
 * @author dycc
 *
 */
public class GZIPResponseStream extends ServletOutputStream{

	protected HttpServletResponse response = null;
	protected ServletOutputStream out = null;
	protected ByteArrayOutputStream baos = null;
	protected GZIPOutputStream gzipos = null;
	protected boolean closed = false;
	
	public GZIPResponseStream(HttpServletResponse response)throws IOException{
		super();
		this.response = response;
		this.out = response.getOutputStream();
		this.baos = new ByteArrayOutputStream();
		this.gzipos = new GZIPOutputStream(this.baos);
		this.closed = false;
	}
	@Override
	public void write(int b) throws IOException {
		if (closed){
			throw new IOException("Cannot write to a closed output stream.");
		}
		gzipos.write(b);
	}
	@Override
	public void write(byte[] b) throws IOException {
		write(b,0,b.length);
	}
	@Override
	public void write(byte[] buf, int off, int len) throws IOException {
		if (closed){
			throw new IOException("Cannot write to a closed output stream.");
		}
		gzipos.write(buf, off, len);
	}
	@Override
	public void flush() throws IOException {
		if (closed){
			throw new IOException("Cannot flush a closed output stream.");
		}
		gzipos.flush();
	}
	@Override
	public void close() throws IOException {
		if (closed){
			return;
		}
		gzipos.finish();
		byte[] buf = this.baos.toByteArray();
		response.addHeader("Content-Length", Integer.toString(buf.length));
		response.addHeader("Content-Encoding", "gzip");
		out.write(buf);
		out.flush();
		out.close();
		closed = true;
	}
}

 

2. END