Struts2与DWR在项目中的共存解决方案

柔光的暖阳◎ 2021-09-14 00:30 254阅读 0赞

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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/.\*