Javascript开发之js压缩篇

Extjs可以说是目前最优秀的js开发库了。除了那个蹩脚的GPLV3授权。
但是使用中遇到的第一个问题就是，Extjs那庞大的个头。想办法压缩ExtJS的大小成了首先要解决的问题。
谈谈我的解决方法，欢迎拍砖。突然发现前面那个广告贴被锁了  

1、压缩混淆
   除了ExtJS的大个子以外，引用的很多其他的js库，项目中自己的js文件等等。采用OPOA组件式开发最后一定会增大js文件的总量。所以项目后期要对这些文件进行压缩合并。现在流行的js压缩工具有很多，如packer,jsMin,Esc,JSA,yui-compressor等等。经过实际使用我选的是yui-compressor.
   yui-compressor项目地址：http://developer.yahoo.com/yui/compressor/
下载后得到一个java开发的jar包。使用方法基于命令行:
   java -jar yuicompressor-x.y.z.jar [options] [input file]
开发中的js文件不可能一个个的手动压缩，这里用到了ANT。在项目构建中可以替你完成以上任务。

<property name="yuicompressor" value="${tools}/yuicompressor-2.3.6.jar" />
      <apply executable="java" parallel="false" verbose="true" dest="${dist}/WebRoot">
          <fileset dir="${dist}/WebRoot">
	          <include name="modules/*.js" />
	          <include name="js/*.js" />
          </fileset>
          <arg line="-jar" />
          <arg path="${yuicompressor}" />
          <arg line="--type js --charset UTF-8 -o" />
          <targetfile />
          <mapper type="glob" from="*.js" to="*-m.js" />
      </apply>
      <concat destfile="${dist}/WebRoot/js/base.js" encoding="UTF-8" >
          <fileset dir="${dist}/WebRoot/js">
              <include name="*-m.js" />
          </fileset>
      </concat>
      <concat destfile="${dist}/WebRoot/modules/modules.js" encoding="UTF-8" >
          <fileset dir="${dist}/WebRoot/modules">
              <include name="*-m.js" />
          </fileset>
      </concat>
      <delete>
          <fileset dir="${dist}/WebRoot">
              <include name="js/*.js"/>
              <include name="modules/*.js"/>
              <exclude name="modules/modules.js" />
              <exclude name="js/base.js" />
          </fileset>
      </delete>

2、gzip压缩。
   坛子里讨论的gzip压缩有2种，
   一是有的容器（服务器）提供的功能，但这个局限于特定容器。比如apache+tomcat或者resin-pro版。
   二是部署前手动gzip压缩，配合servlet过滤器使用，这个能实现gzip功能，但是降低了灵活性。
   我自己用的是自己的实现，采用gzip servlet filter实现。下面是我的代码参考网上内容.

package sh.blog.util.web.filter;

import java.io.IOException;

import java.util.zip.GZIPOutputStream;

import javax.servlet.ServletOutputStream;

public class CompressedStream extends ServletOutputStream {
	
	private ServletOutputStream out;
	private GZIPOutputStream    gzip;

	/**
	 * 指定压缩缓冲流
	 * @param 输出流到压缩
	 * @throws IOException if an error occurs with the {@link GZIPOutputStream}.
	 */
	public CompressedStream(ServletOutputStream out) throws IOException {
		this.out = out;
		reset();
	}

	/** @see ServletOutputStream * */
	public void close() throws IOException {
		gzip.close();
	}

	/** @see ServletOutputStream * */
	public void flush() throws IOException {
		gzip.flush();
	}

	/** @see ServletOutputStream * */
	public void write(byte[] b) throws IOException {
		write(b, 0, b.length);
	}

	/** @see ServletOutputStream * */
	public void write(byte[] b, int off, int len) throws IOException {
		gzip.write(b, off, len);
	}

	/** @see ServletOutputStream * */
	public void write(int b) throws IOException {
		gzip.write(b);
	}

	/**
	 * Resets the stream.
	 * 
	 * @throws IOException if an I/O error occurs.
	 */
	public void reset() throws IOException {
		gzip = new GZIPOutputStream(out);
	}
}

package sh.blog.util.web.filter;

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

import javax.servlet.ServletOutputStream;

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

public class CompressionResponse extends HttpServletResponseWrapper {
	
	protected HttpServletResponse response;
	private ServletOutputStream out;
	private CompressedStream compressedOut;
	private PrintWriter writer;
	protected int contentLength;

	/**
	 * 创建一个新的被压缩响应给HTTP
	 * 
	 * @param response the HTTP response to wrap.
	 * @throws IOException if an I/O error occurs.
	 */
	public CompressionResponse(HttpServletResponse response) throws IOException {
		super(response);
		this.response = response;
		compressedOut = new CompressedStream(response.getOutputStream());
	}

	/**
	 * Ignore attempts to set the content length since the actual content length
	 * will be determined by the GZIP compression.
	 * 
	 * @param len the content length
	 */
	public void setContentLength(int len) {
		contentLength = len;
	}

	/** @see HttpServletResponse * */
	public ServletOutputStream getOutputStream() throws IOException {
		if (null == out) {
			if (null != writer) {
				throw new IllegalStateException("getWriter() has already been called on this response.");
			}
			out = compressedOut;
		}
		return out;
	}

	/** @see HttpServletResponse * */
	public PrintWriter getWriter() throws IOException {
		if (null == writer) {
			if (null != out) {
				throw new IllegalStateException("getOutputStream() has already been called on this response.");
			}
			writer = new PrintWriter(compressedOut);
		}
		return writer;
	}

	/** @see HttpServletResponse * */
	public void flushBuffer() {
		try {
			if (writer != null) {
				writer.flush();
			} else if (out != null) {
				out.flush();
			}
		} catch (IOException e) {
			e.printStackTrace();
		}
	}

	/** @see HttpServletResponse * */
	public void reset() {
		super.reset();
		try {
			compressedOut.reset();
		} catch (IOException e) {
			throw new RuntimeException(e);
		}
	}

	/** @see HttpServletResponse * */
	public void resetBuffer() {
		super.resetBuffer();
		try {
			compressedOut.reset();
		} catch (IOException e) {
			throw new RuntimeException(e);
		}
	}

	/**
	 * Finishes writing the compressed data to the output stream. Note: this
	 * closes the underlying output stream.
	 * 
	 * @throws IOException if an I/O error occurs.
	 */
	public void close() throws IOException {
		compressedOut.close();
	}
}

/**
 * 如果浏览器支持解压缩,则压缩该代码
 * @throws IOException ServletException if an error occurs with the {@link GZIPOutputStream}.
 * 如果需要开启该过滤器,在web.xml中加入此代码
    <filter>
      <filter-name>gzip</filter-name>
      <filter-class>com.strongit.finance.gzip</filter-class>
    </filter>
    <filter-mapping>
      <filter-name>gzip</filter-name>
      <url-pattern>*.jsp</url-pattern>
    </filter-mapping>
 */

package sh.blog.util.web.filter;

import java.io.IOException;

import java.util.Enumeration;

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;

import org.apache.commons.logging.Log;
import org.apache.commons.logging.LogFactory;


public class CompressionFilter implements Filter {

	protected Log log = LogFactory.getFactory().getInstance(this.getClass().getName());

    @SuppressWarnings("unchecked")
	public void doFilter(ServletRequest request, ServletResponse response,
            FilterChain chain) throws IOException, ServletException {
    	
        boolean compress = false;
        if (request instanceof HttpServletRequest){
            HttpServletRequest httpRequest = (HttpServletRequest) request;
            Enumeration headers = httpRequest.getHeaders("Accept-Encoding");
            while (headers.hasMoreElements()){
                String value = (String) headers.nextElement();
                if (value.indexOf("gzip") != -1){
                    compress = true;
                }
            }
        }
        
        if (compress){//如果浏览器支持则压缩
            HttpServletResponse httpResponse = (HttpServletResponse) response;
            httpResponse.addHeader("Content-Encoding", "gzip");
            CompressionResponse compressionResponse= new CompressionResponse(httpResponse);
            chain.doFilter(request, compressionResponse);
            compressionResponse.close();
        }
        else{//如果浏览器不支持则不压缩
            chain.doFilter(request, response);
        }
    }
    
    
    public void init(FilterConfig config) throws ServletException {
        
    }

    public void destroy(){
        
    }
}

实际使用的效果以 http://demo.slivercrm.cn:8084为例

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