java servlet Filter实现gzip压缩机制的源代码分享

在java提供接口给客户端开发中，可以启动gzip压缩机制来达到减小文件大小的目的。

相关java代码如下：

GZIPFilter.java

package com.zuidaima.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;

public class GZIPFilter implements Filter {

	public void doFilter(ServletRequest req, ServletResponse res,
			FilterChain chain) throws IOException, ServletException {
		if (req instanceof HttpServletRequest) {
			HttpServletRequest request = (HttpServletRequest) req;
			HttpServletResponse response = (HttpServletResponse) res;
			boolean isGzip = false;
			String gzip = request.getParameter("gzip");//根据请求参数启用gzip机制
			if (gzip != null && gzip.equals("true")) {
				isGzip = true;
			}

			String ae = request.getHeader("Accept-Encoding");
			if (ae != null && ae.indexOf("gzip") != -1) {//根据客户端agent请求参数来启用gzip机制
				isGzip = true;
			}
			if (isGzip) {
				GZIPResponseWrapper wrappedResponse = new GZIPResponseWrapper(
						response);
				chain.doFilter(req, wrappedResponse);
				wrappedResponse.finishResponse();
				return;
			}
			chain.doFilter(req, res);
		}
	}

	public void init(FilterConfig filterConfig) {
	}

	public void destroy() {
	}
}

GZIPResponseStream.java

package com.zuidaima.filter;

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

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

public class GZIPResponseStream extends ServletOutputStream {
	protected ByteArrayOutputStream baos = null;
	protected GZIPOutputStream gzipstream = null;
	protected boolean closed = false;
	protected HttpServletResponse response = null;
	protected ServletOutputStream output = null;

	public GZIPResponseStream(HttpServletResponse response) throws IOException {
		super();
		closed = false;
		this.response = response;
		this.output = response.getOutputStream();
		baos = new ByteArrayOutputStream();
		gzipstream = new GZIPOutputStream(baos);
	}

	public void close() throws IOException {
		if (closed) {
			throw new IOException("This output stream has already been closed");
		}
		gzipstream.finish();

		byte[] bytes = baos.toByteArray();

		response.addHeader("Content-Length", Integer.toString(bytes.length));
		response.addHeader("Content-Encoding", "gzip");
		output.write(bytes);
		output.flush();
		output.close();
		closed = true;
	}

	public void flush() throws IOException {
		if (closed) {
			throw new IOException("Cannot flush a closed output stream");
		}
		gzipstream.flush();
	}

	public void write(int b) throws IOException {
		if (closed) {
			throw new IOException("Cannot write to a closed output stream");
		}
		gzipstream.write((byte) b);
	}

	public void write(byte b[]) throws IOException {
		write(b, 0, b.length);
	}

	public void write(byte b[], int off, int len) throws IOException {
		if (closed) {
			throw new IOException("Cannot write to a closed output stream");
		}
		gzipstream.write(b, off, len);
	}

	public boolean closed() {
		return (this.closed);
	}

	public void reset() {
		// noop
	}
}

GZIPResponseWrapper.java

package com.zuidaima.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;

public class GZIPResponseWrapper extends HttpServletResponseWrapper {
	protected HttpServletResponse origResponse = null;
	protected ServletOutputStream stream = null;
	protected PrintWriter writer = null;

	public GZIPResponseWrapper(HttpServletResponse response) {
		super(response);
		origResponse = response;
	}

	public ServletOutputStream createOutputStream() throws IOException {
		return (new GZIPResponseStream(origResponse));
	}

	public void finishResponse() {
		try {
			if (writer != null) {
				writer.close();
			} else {
				if (stream != null) {
					stream.close();
				}
			}
		} catch (IOException e) {
		}
	}

	public void flushBuffer() throws IOException {
		stream.flush();
	}

	public ServletOutputStream getOutputStream() throws IOException {
		if (writer != null) {
			throw new IllegalStateException(
					"getWriter() has already been called!");
		}

		if (stream == null)
			stream = createOutputStream();
		return (stream);
	}

	public PrintWriter getWriter() throws IOException {
		if (writer != null) {
			return (writer);
		}

		if (stream != null) {
			throw new IllegalStateException(
					"getOutputStream() has already been called!");
		}

		stream = createOutputStream();
		writer = new PrintWriter(new OutputStreamWriter(stream, "UTF-8"));
		return (writer);
	}

	public void setContentLength(int length) {
	}
}

web.xml中配置如下：

<filter>
	<filter-name>GZIPFilter</filter-name>
	<filter-class>com.zuidaima.filter.GZIPFilter</filter-class>
</filter>
<filter-mapping>
	<filter-name>GZIPFilter</filter-name>
	<url-pattern>*.htm</url-pattern>
</filter-mapping>

未启用gzip压缩前响应头信息：

启用gizp压缩后响应头信息：