1. 压缩技术对网站访问速度的提升
压缩技术是一种将数据进行压缩以减少其大小的过程。通过使用压缩技术,可以将Java网站上的静态和动态内容(如JavaScript、HTML和CSS文件等)压缩成更小的文件,以加快页面加载速度并节省带宽。
在网站访问过程中,每当用户在浏览器中请求某个页面时,服务器都会向用户的计算机发送所请求的页面。如果这个页面没有被压缩,那么它的大小将非常庞大,会导致页面加载时间过长。而如果使用了压缩技术,服务器将会在发送该页面之前将其压缩成更小的文件,这样就可以减少页面的加载时间。此外,压缩技术还可以降低页面的带宽消耗,从而减少网站所需的带宽资源。
1.1 压缩技术的种类
目前,常用的压缩技术有两种:Gzip和Deflate。
1.1.1 Gzip
Gzip是目前使用最广泛的压缩技术之一,它可以将文件压缩成一个更小的文件,以便于传输。它可以压缩不仅是HTML文件,还可以压缩JavaScript、CSS、XML等类型的文件。
// 使用Gzip对HTTP响应进行压缩
public class GzipFilter implements Filter {
@Override
public void doFilter(ServletRequest request, ServletResponse response, FilterChain chain) throws IOException, ServletException {
HttpServletResponse resp = (HttpServletResponse) response;
resp.setHeader("Content-Encoding", "gzip");
GzipResponseWrapper wrapper = new GzipResponseWrapper(resp);
chain.doFilter(request, wrapper);
wrapper.finish();
}
}
1.1.2 Deflate
Deflate是另一种广泛使用的压缩技术,它与Gzip类似,也可以压缩HTML、JavaScript、CSS、XML等类型的文件。然而,与Gzip相比,Deflate需要更少的CPU资源,因此对于资源受限的环境来说,Deflate可能更加适用。
// 使用Deflate对HTTP响应进行压缩
public class DeflateFilter implements Filter {
@Override
public void doFilter(ServletRequest request, ServletResponse response, FilterChain chain) throws IOException, ServletException {
HttpServletResponse resp = (HttpServletResponse) response;
resp.setHeader("Content-Encoding", "deflate");
DeflateResponseWrapper wrapper = new DeflateResponseWrapper(resp);
chain.doFilter(request, wrapper);
wrapper.finish();
}
}
1.2 压缩技术的实现方式
在Java中,实现压缩技术主要有两种方式:使用过滤器或使用Web容器自带的压缩功能。
1.2.1 使用过滤器
使用过滤器可以自定义压缩策略,比如选择使用Gzip还是Deflate。以下是一个使用过滤器实现压缩的示例:
public abstract class CompressionFilter implements Filter {
private final CompressionStrategy strategy;
public CompressionFilter(CompressionStrategy strategy) {
this.strategy = strategy;
}
public void doFilter(ServletRequest request, ServletResponse response, FilterChain chain) throws IOException, ServletException {
doFilterInternal(request, wrapResponse((HttpServletResponse) response), chain);
}
protected HttpServletResponse wrapResponse(HttpServletResponse response) {
return new CompressionResponseWrapper(response, strategy);
}
protected abstract void doFilterInternal(ServletRequest request, HttpServletResponse response, FilterChain chain) throws IOException, ServletException;
public void init(FilterConfig filterConfig) throws ServletException {}
public void destroy() {}
}
public interface CompressionStrategy {
OutputStream wrapOutputStream(OutputStream outputStream) throws IOException;
String getContentEncoding();
}
public class GzipCompressionStrategy implements CompressionStrategy {
public OutputStream wrapOutputStream(OutputStream outputStream) throws IOException {
return new GZIPOutputStream(outputStream);
}
public String getContentEncoding() {
return "gzip";
}
}
public class DeflateCompressionStrategy implements CompressionStrategy {
public OutputStream wrapOutputStream(OutputStream outputStream) throws IOException {
return new DeflaterOutputStream(outputStream);
}
public String getContentEncoding() {
return "deflate";
}
}
public class CompressionResponseWrapper extends HttpServletResponseWrapper {
private final CompressionStrategy strategy;
private ByteArrayOutputStream output;
private PrintWriter writer;
public CompressionResponseWrapper(HttpServletResponse response, CompressionStrategy strategy) {
super(response);
this.strategy = strategy;
this.output = new ByteArrayOutputStream();
}
public String getContentType() {
return super.getContentType();
}
public ServletOutputStream getOutputStream() throws IOException {
return new CompressionOutputStream(super.getOutputStream(), strategy.wrapOutputStream(output));
}
public PrintWriter getWriter() throws IOException {
if (writer == null) {
writer = new PrintWriter(new OutputStreamWriter(getOutputStream(), getCharacterEncoding()));
}
return writer;
}
public void setContentLength(int contentLength) {}
public void flushBuffer() throws IOException {
if (writer != null) {
writer.flush();
} else if (output.size() > 0) {
super.setContentLength(output.size());
ByteArrayInputStream input = new ByteArrayInputStream(output.toByteArray());
OutputStream output = super.getOutputStream();
try {
IOUtils.copy(input, output);
output.flush();
} finally {
IOUtils.closeQuietly(output);
IOUtils.closeQuietly(input);
}
}
super.flushBuffer();
}
public void reset() {
super.reset();
this.output = new ByteArrayOutputStream();
}
public String getContentEncoding() {
return strategy.getContentEncoding();
}
}
public class CompressionOutputStream extends ServletOutputStream {
private final OutputStream outputStream;
public CompressionOutputStream(OutputStream outputStream, OutputStream compressed) {
this.outputStream = outputStream;
this.compressed = compressed;
}
public void write(int b) throws IOException {
compressed.write(b);
}
public void flush() throws IOException {
compressed.flush();
}
public void close() throws IOException {
compressed.close();
outputStream.close();
}
}
1.2.2 使用Web容器自带的压缩功能
与使用过滤器实现压缩相比,使用Web容器自带的压缩功能更加简单明了。在Tomcat中,只需要在Web应用程序的web.xml文件中添加以下配置即可:
<web-app xmlns="http://java.sun.com/xml/ns/javaee" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:schemaLocation="http://java.sun.com/xml/ns/javaee http://java.sun.com/xml/ns/javaee/web-app_3_0.xsd" version="3.0">
<display-name>MyWebApp</display-name>
<filter>
<display-name>CompressionFilter</display-name>
<filter-name>CompressionFilter</filter-name>
<filter-class>org.apache.catalina.filters.CompressionFilter</filter-class>
<init-param>
<param-name>compression</param-name>
<param-value>on</param-value>
</init-param>
<init-param>
<param-name>compressableMimeType</param-name>
<param-value>text/html,text/xml,text/plain,text/css,text/javascript,application/javascript,application/json,application/xml</param-value>
</init-param>
</filter>
<filter-mapping>
<filter-name>CompressionFilter</filter-name>
<url-pattern>/*</url-pattern>
</filter-mapping>
</web-app>
2. 结论
通过使用压缩技术,可以加快Java网站的访问速度并节省带宽。在选择压缩技术时,应该考虑到Web应用程序的性能和组织特性。在实现压缩时,可以使用过滤器或Web容器自带的压缩功能。