一、GZip压缩介绍
GZip是一种数据压缩算法,它使用Lempel-Ziv算法(LZ77)和哈夫曼编码来压缩数据。它可以压缩任何数据类型,但最适用于纯文本文件,例如HTML、CSS和JavaScript文件。GZip使用DEFLATE算法来实现数据压缩和解压缩。
在Java中,GZip压缩功能由java.util.zip.GZIPOutputStream和java.util.zip.GZIPInputStream类提供。
二、GZip压缩的优点
1、文件大小明显缩小。对于大型文本文件(如日志文件、XML文件等),GZip压缩可以将文件大小缩小到原来的1/3或1/4。
2、网络传输效率提高。通过使用GZip压缩,可以减少数据传输量,从而提高网络传输效率,特别是在低速网络或网络拥塞情况下。
3、更安全的数据传输。GZip压缩可以提高数据的安全性,因为压缩后的文件更难以解密。
三、使用GZip压缩和解压缩文件
GZip压缩和解压缩文件的方法如下:
import java.util.zip.*; import java.io.*; public class GZipDemo { public static void main(String[] args) { String fileToCompress = "example.txt"; String compressedFile = "example.txt.gz"; String decompressedFile = "exampleCopy.txt"; compressFile(fileToCompress, compressedFile); decompressFile(compressedFile, decompressedFile); } public static void compressFile(String fileToCompress, String compressedFile) { try { FileInputStream fileInputStream = new FileInputStream(fileToCompress); FileOutputStream fileOutputStream = new FileOutputStream(compressedFile); GZIPOutputStream gzipOutputStream = new GZIPOutputStream(fileOutputStream); byte[] buffer = new byte[1024]; int bytesRead; while ((bytesRead = fileInputStream.read(buffer)) > 0) { gzipOutputStream.write(buffer, 0, bytesRead); } fileInputStream.close(); gzipOutputStream.finish(); gzipOutputStream.close(); System.out.println("File " + fileToCompress + " has been compressed to " + compressedFile + "."); } catch (IOException ex) { ex.printStackTrace(); } } public static void decompressFile(String compressedFile, String decompressedFile) { try { FileInputStream fileInputStream = new FileInputStream(compressedFile); GZIPInputStream gzipInputStream = new GZIPInputStream(fileInputStream); FileOutputStream fileOutputStream = new FileOutputStream(decompressedFile); byte[] buffer = new byte[1024]; int bytesRead; while ((bytesRead = gzipInputStream.read(buffer)) > 0) { fileOutputStream.write(buffer, 0, bytesRead); } gzipInputStream.close(); fileOutputStream.close(); System.out.println("File " + compressedFile + " has been decompressed to " + decompressedFile + "."); } catch (IOException ex) { ex.printStackTrace(); } } }
上述示例代码演示了如何压缩和解压缩文件。首先,我们创建了一个包含要压缩的文件的字符串,一个包含压缩文件的字符串和一个包含解压缩文件的字符串。然后,我们使用compressFile()方法压缩原始文件,并使用decompressFile()方法解压缩压缩文件。
四、GZip压缩HTTP响应
GZip压缩可以通过HTTP传输减少响应大小,从而提高网络传输效率。可以使用Java Servlet API的GZipFilter类来轻松实现GZip压缩HTTP响应。
以下是一个使用GZipFilter类进行HTTP响应压缩的示例:
import java.io.IOException; import javax.servlet.ServletException; import javax.servlet.ServletRequest; import javax.servlet.ServletResponse; import javax.servlet.http.HttpServletRequest; import javax.servlet.http.HttpServletResponse; import javax.servlet.http.HttpServletResponseWrapper; import javax.servlet.http.HttpServlet; public class GZipServlet extends HttpServlet { static final String ENCODING_HEADER = "Content-Encoding"; static final String ENCODING = "gzip"; public void service(ServletRequest req, ServletResponse res) throws ServletException, IOException { HttpServletRequest request = (HttpServletRequest) req; HttpServletResponse response = (HttpServletResponse) res; String acceptEncoding = request.getHeader("Accept-Encoding"); if (acceptEncoding != null && acceptEncoding.indexOf(ENCODING) >= 0) { GZipServletResponseWrapper gzipResponse = new GZipServletResponseWrapper(response); gzipResponse.setCompressionThreshold(256); try { super.service(request, gzipResponse); } finally { gzipResponse.finishResponse(); } return; } super.service(request, response); } private static class GZipServletResponseWrapper extends HttpServletResponseWrapper { protected HttpServletResponse response = null; protected GZipServletOutputStream gzipOutputStream = null; protected PrintWriter printWriter = null; protected int compressionThreshold = 0; public GZipServletResponseWrapper(HttpServletResponse response) throws IOException { super(response); this.response = response; } public void setCompressionThreshold(int compressionThreshold) { this.compressionThreshold = compressionThreshold; } private void finishResponse() throws IOException { if (this.printWriter != null) { this.printWriter.close(); } if (this.gzipOutputStream != null) { this.gzipOutputStream.close(); } } public void flushBuffer() throws IOException { if (this.printWriter != null) { this.printWriter.flush(); } IOException exception1 = null; try { if (this.gzipOutputStream != null) { this.gzipOutputStream.flush(); } } catch (IOException ex) { exception1 = ex; } IOException exception2 = null; try { super.flushBuffer(); } catch (IOException ex) { exception2 = ex; } if (exception1 != null) { throw exception1; } if (exception2 != null) { throw exception2; } } public ServletOutputStream getOutputStream() throws IOException { if (this.printWriter != null) { throw new IllegalStateException("PrintWriter obtained already - cannot get OutputStream"); } if (this.gzipOutputStream == null) { this.gzipOutputStream = new GZipServletOutputStream(this.response.getOutputStream()); this.response.addHeader(ENCODING_HEADER, ENCODING); } return this.gzipOutputStream; } public PrintWriter getWriter() throws IOException { if (this.printWriter == null && this.gzipOutputStream != null) { throw new IllegalStateException("OutputStream obtained already - cannot get PrintWriter"); } if (this.printWriter == null) { this.gzipOutputStream = new GZipServletOutputStream(this.response.getOutputStream()); this.response.addHeader(ENCODING_HEADER, ENCODING); this.printWriter = new PrintWriter(new OutputStreamWriter(this.gzipOutputStream, this.response.getCharacterEncoding())); } return this.printWriter; } } private static class GZipServletOutputStream extends ServletOutputStream { protected OutputStream outputStream = null; public GZipServletOutputStream(OutputStream outputStream) throws IOException { super(); this.outputStream = outputStream; } public void close() throws IOException { this.outputStream.close(); super.close(); } public void flush() throws IOException { this.outputStream.flush(); } public void write(byte[] b) throws IOException { this.outputStream.write(b); } public void write(byte[] b, int off, int len) throws IOException { this.outputStream.write(b, off, len); } public void write(int b) throws IOException { this.outputStream.write(b); } } }
上述示例代码演示了如何使用GZipFilter类将HTTP响应压缩并发送给客户端。在GZipServlet中,我们首先检查浏览器是否支持GZip压缩,如果支持,我们将响应包装在一个GZipServletResponseWrapper中,然后使用GZipServletOutputStream类将响应压缩。最后,我们在响应头中添加Content-Encoding:gzip标头,并发送响应。