使用JAVA實作JS/CSS的gzip壓縮功能

<filter>
		<filter-name>ZGIPFilter</filter-name>
		<filter-class>com.ztesoft.zsmart.web.filter.ZGIPFilter</filter-class>
	</filter>
	<filter-mapping>
		<filter-name>ZGIPFilter</filter-name>
		<url-pattern>*.js</url-pattern>
	</filter-mapping>
	<filter-mapping>
		<filter-name>ZGIPFilter</filter-name>
		<url-pattern>*.css</url-pattern>
	</filter-mapping>      

public class ZGIPFilter extends HttpServlet implements Filter {

    public void doFilter(ServletRequest request, ServletResponse response, FilterChain chain) throws IOException,
        ServletException {
        // 判斷是否包含了 Accept-Encoding 請求頭部
        HttpServletRequest s = (HttpServletRequest) request;
        String header = s.getHeader("Accept-Encoding");
        if (header != null && header.toLowerCase().contains("gzip")) {
            HttpServletResponse resp = (HttpServletResponse) response;
            final ByteArrayOutputStream buffer = new ByteArrayOutputStream();

            HttpServletResponseWrapper hsrw = new HttpServletResponseWrapper(resp) {
                @Override
                public PrintWriter getWriter() throws IOException {
                    return new PrintWriter(new OutputStreamWriter(buffer, getCharacterEncoding()));
                }

                @Override
                public ServletOutputStream getOutputStream() throws IOException {
                    return new ServletOutputStream() {
                        @Override
                        public void write(int b) throws IOException {
                            buffer.write(b);
                        }
                    };
                }
            };

            chain.doFilter(request, hsrw);
            byte[] gzipData = gzip(buffer.toByteArray());
            resp.addHeader("Content-Encoding", "gzip");
            resp.setContentLength(gzipData.length);
            ServletOutputStream output = response.getOutputStream();
            output.write(gzipData);
            output.flush();
        }
        else {
            chain.doFilter(request, response);
        }
    }

    // 用 GZIP 壓縮位元組數組
    private byte[] gzip(byte[] data) {
        ByteArrayOutputStream byteOutput = new ByteArrayOutputStream(10240);
        GZIPOutputStream output = null;
        try {
            output = new GZIPOutputStream(byteOutput);
            output.write(data);
        }
        catch (IOException e) {
        }
        finally {
            try {
                output.close();
            }
            catch (IOException e) {
            }
        }
        return byteOutput.toByteArray();
    }
}
           

 GZIP前

  GZIP後

 結論：如果伺服器端未采用gzip格式壓縮，可以通過這樣的配置實作。由上圖看出來，檔案壓縮之後大小由原來的94890變成33673，将近減小了三分之二，還是可觀的。這裡隻配置了JS和CSS的壓縮，HTML靜态頁面應可以使用，圖檔使用GZIP壓縮會有點問題(以png為例，大小由原來的480605變成了480736，反而變大了)。