Liferay MinifierFilter的研究

大家都知道，在Web应用程序中，为了节省网络开销，往往吧多个小的js文件整合成一个大的js文件，吧多个小的css文件整合成一个大的js文件,这样原本N次小文件的请求就可以合并成单次的网络请求。最典型的做这件事情的工具是大名鼎鼎的yui-compressor.

其实在Liferay中，我们为了达到合并css,js的目的，用了不同于yui-compressor的方法，这就是我们的主角 MinifierFilter.

既然是Filter，那么它肯定有filter-mapping，我们轻易的在liferay-web.xml中找到了Filter的定义和Filter的mapping.

 
 

  
  
... 
  
  
<filter> 
  
  
        <filter-name>Minifier Filter</filter-name> 
  
  
        <filter-class>com.liferay.portal.servlet.filters.minifier.MinifierFilter</filter-class> 
  
  
    </filter> 
  
  
<filter> <filter-name>Minifier Filter - JSP</filter-name> <filter-class>com.liferay.portal.servlet.filters.minifier.MinifierFilter</filter-class> <init-param> <param-name>url-regex-pattern</param-name> <param-value>.+/(aui_lang|barebone|css|everything|main)\.jsp</param-value> </init-param> </filter>
  
  
 
  
  
... 
  
  
<filter-mapping> 
  
  
        <filter-name>Minifier Filter</filter-name> 
  
  
        <url-pattern>*.css</url-pattern> 
  
  
    </filter-mapping> 
  
  
    <filter-mapping> 
  
  
        <filter-name>Minifier Filter</filter-name> 
  
  
        <url-pattern>*.js</url-pattern> 
  
  
    </filter-mapping> 
  
  
<filter-mapping> <filter-name>Minifier Filter - JSP</filter-name> <url-pattern>*.jsp</url-pattern> </filter-mapping>
  
  
... 
 
 

所以，我们可以看到，当客户端对Liferay服务器上请求任意css或者javascript资源时候，都会被这个MinifierFilter所过滤，我们现在就来看下庐山真面目。

因为MinifierFilter最终实现了Filter接口，而doFilter方法在父类的父类BaseFilter中定义，这个doFilter仅仅是调用processFilter()方法，

 
 

  
  
public void doFilter( 
  
  
            ServletRequest servletRequest, ServletResponse servletResponse, 
  
  
            FilterChain filterChain) 
  
  
        throws IOException, ServletException { 
  
  
 
  
  
        try { 
  
  
            HttpServletRequest request = (HttpServletRequest)servletRequest; 
  
  
            HttpServletResponse response = (HttpServletResponse)servletResponse; 
  
  
 
  
  
            processFilter(request, response, filterChain); 
  
  
        } 
  
  
        catch (IOException ioe) { 
  
  
            throw ioe; 
  
  
        } 
  
  
        catch (ServletException se) { 
  
  
            throw se; 
  
  
        } 
 
 

所以这就是我们的入口：

 
 

  
  
protected void processFilter( 
  
  
            HttpServletRequest request, HttpServletResponse response, 
  
  
            FilterChain filterChain) 
  
  
        throws Exception { 
  
  
 
  
  
        Object minifiedContent = getMinifiedContent( 
  
  
            request, response, filterChain); 
  
  
 
  
  
        if (minifiedContent == null) { 
  
  
            minifiedContent = getMinifiedBundleContent(request, response); 
  
  
        } 
  
  
 
  
  
        if (minifiedContent == null) { 
  
  
            processFilter(MinifierFilter.class, request, response, filterChain); 
  
  
        } 
  
  
        else { 
  
  
            if (minifiedContent instanceof File) { 
  
  
                ServletResponseUtil.write(response, (File)minifiedContent); 
  
  
            } 
  
  
            else if (minifiedContent instanceof String) { 
  
  
                ServletResponseUtil.write(response, (String)minifiedContent); 
  
  
            } 
  
  
        } 
  
  
    } 
 
 

首先，它会去执行06-07行的getMinifiedContent()方法,它会调用以下代码：

 
 

  
  
protected Object getMinifiedContent( 
  
  
            HttpServletRequest request, HttpServletResponse response, 
  
  
            FilterChain filterChain) 
  
  
        throws Exception { 
  
  
 
  
  
        .. 
  
  
 
  
  
       ..
  
  
 
  
  
        String minifiedContent = null; 
  
  
 
  
  
        if (realPath.endsWith(_CSS_EXTENSION)) { 
  
  
            if (_log.isInfoEnabled()) { 
  
  
                _log.info("Minifying CSS " + file); 
  
  
            } 
  
  
 
  
  
            minifiedContent = minifyCss(request, response, file); 
  
  
 
  
  
            response.setContentType(ContentTypes.TEXT_CSS); 
  
  
 
  
  
            FileUtil.write(cacheContentTypeFile, ContentTypes.TEXT_CSS); 
  
  
        } 
  
  
        else if (realPath.endsWith(_JAVASCRIPT_EXTENSION)) { 
  
  
            if (_log.isInfoEnabled()) { 
  
  
                _log.info("Minifying JavaScript " + file); 
  
  
            } 
  
  
 
  
  
            minifiedContent = minifyJavaScript(file); 
  
  
 
  
  
            response.setContentType(ContentTypes.TEXT_JAVASCRIPT); 
  
  
 
  
  
            FileUtil.write(cacheContentTypeFile, ContentTypes.TEXT_JAVASCRIPT); 
  
  
        } 
  
  
        else if (realPath.endsWith(_JSP_EXTENSION)) { 
  
  
            if (_log.isInfoEnabled()) { 
  
  
                _log.info("Minifying JSP " + file); 
  
  
            } 
  
  
 
  
  
            StringServletResponse stringResponse = new StringServletResponse( 
  
  
                response); 
  
  
 
  
  
            processFilter( 
  
  
                MinifierFilter.class, request, stringResponse, filterChain); 
  
  
 
  
  
            CacheResponseUtil.setHeaders(response, stringResponse.getHeaders()); 
  
  
 
  
  
            response.setContentType(stringResponse.getContentType()); 
  
  
 
  
  
            minifiedContent = stringResponse.getString(); 
  
  
 
  
  
            if (minifierType.equals("css")) { 
  
  
                minifiedContent = minifyCss( 
  
  
                    request, response, realPath, minifiedContent); 
  
  
            } 
  
  
            else if (minifierType.equals("js")) { 
  
  
                minifiedContent = minifyJavaScript(minifiedContent); 
  
  
            } 
  
  
 
  
  
            FileUtil.write( 
  
  
                cacheContentTypeFile, stringResponse.getContentType()); 
  
  
        } 
  
  
        else { 
  
  
            return null; 
  
  
        } 
  
  
 
  
  
        FileUtil.write(cacheDataFile, minifiedContent); 
  
  
 
  
  
        return minifiedContent; 
  
  
    }