又一篇讲Struts2和dwr共存的文章

1.struts2和dwr为什么会冲突?

最近很多同学都在问同样一个问题,struts2和dwr该如何共存?我们先分析一下为什么会出现冲突.

struts2通过StrutsPrepareAndExecuteFilter过滤器来处理请求,常见的配置如下:

 <filter>
  <filter-name>struts2</filter-name>
  <filter-class>org.apache.struts2.dispatcher.ng.filter.StrutsPrepareAndExecuteFilter</filter-class>
 </filter>
 <filter-mapping>
  <filter-name>struts2</filter-name>
  <url-pattern>/*</url-pattern>
 </filter-mapping>

问题就在这里,<url-pattern>/*</url-pattern>配置过滤了所有的请求,当用户提交的请求是/dwr/*时,也同样被StrutsPrepareAndExecuteFilter处理了,根本达不到DWR框架,这就是为什么二者不能共存的原因.

2.通过struts2源码发现问题

网上我没找到问题的解决方案,所以,只能通过阅读源代码来查找问题的根源了.在StrutsPrepareAndExecuteFilter类中,重写了doFilter方法:

    public void doFilter(ServletRequest req, ServletResponse res, FilterChain chain) throws IOException, ServletException {
 
        HttpServletRequest request = (HttpServletRequest) req;
        HttpServletResponse response = (HttpServletResponse) res;
 
        try {
            prepare.setEncodingAndLocale(request, response);
            prepare.createActionContext(request, response);
            prepare.assignDispatcherToThread();
   if ( excludedPatterns != null && prepare.isUrlExcluded(request, excludedPatterns)) {
    chain.doFilter(request, response);
   } else {
    request = prepare.wrapRequest(request);
    ActionMapping mapping = prepare.findActionMapping(request, response, true);
    if (mapping == null) {
     boolean handled = execute.executeStaticResourceRequest(request, response);
     if (!handled) {
      chain.doFilter(request, response);
     }
    } else {
     execute.executeAction(request, response, mapping);
    }
   }
        } finally {
            prepare.cleanupRequest(request);
        }
    }

注意看粗体部分,如果excludedPatterns不为null且prepare.isUrlExcluded方法的返回值为true,则该请求不交给struts框架处理,那么,sUrlExcluded是如何定义的呢?我们跟踪找到下面的代码:

    public boolean isUrlExcluded( HttpServletRequest request, List<Pattern> excludedPatterns ) {
        if (excludedPatterns != null) {
            String uri = getUri(request);
            for ( Pattern pattern : excludedPatterns ) {
                if (pattern.matcher(uri).matches()) {
                    return true;
                }
            }
        }
        return false;
    }

我们看到,  isUrlExcluded 方法中 excludedPatterns参数是一个List集合, String uri = getUri(request);代码获取请求路径,然后通过一个for循环将请求路径与 excludedPatterns进行匹(,注意,这里是通过正则表达式进行匹配的),如果匹配成功,则返回true,否则返回false.

那么, excludedPatterns的值从哪里来呢?下面的代码是也:

    public List<Pattern> buildExcludedPatternsList( Dispatcher dispatcher ) {
        return buildExcludedPatternsList(dispatcher.getContainer().getInstance(String.class, StrutsConstants.STRUTS_ACTION_EXCLUDE_PATTERN));
    }
            
    private List<Pattern> buildExcludedPatternsList( String patterns ) {
        if (null != patterns && patterns.trim().length() != 0) {
            List<Pattern> list = new ArrayList<Pattern>();
            String[] tokens = patterns.split(",");
            for ( String token : tokens ) {
                list.add(Pattern.compile(token.trim()));
            }
            return Collections.unmodifiableList(list);
        } else {
            return null;
        }
    }

看了上面的代码,是不是豁然开朗?原来, StrutsConstants.STRUTS_ACTION_EXCLUDE_PATTERN常量保存了不由struts2处理的路径,我们在struts2.properties中配置即可.

struts.action.excludePattern=/dwr/.*,/dwr/test/.*

这个文件在struts2-core-2.1.8.1.jar, org.apache.struts2/default.properties中，也可以通过修改struts.xml，在struts标签中加入<constant name="struts.action.excludePattern" value="/dwr.*"></constant>来实现。