Servlet 跳过特定的过滤器Filter

最近维护一个老的SpringMVC的应用，增加CAS单点登录。但是有个特殊的需求是保留系统本身的认证，根据需要可以走CAS单点登录认证，也可以走系统本身的认证。

设计的方案是根据输入的URL进行判断，是否跳过CAS的Filter还是跳过系统本来的认证Filter。

下面上代码：

POM文件：

    org.jasig.cas.client
    cas-client-core
    3.5.0

web.xml

		FirstFilter
		FirstFilter
		
		com.test.filter.FirstFilter
	
	
		FirstFilter
		/*
	
    
    
        CAS Single Sign Out Filter
        org.jasig.cas.client.session.SingleSignOutFilter
        
            casServerUrlPrefix
            http://localhost:8080/cas-server
        
    
    
        CAS Single Sign Out Filter
        *.html
    
    
        CAS Filter
        org.jasig.cas.client.authentication.AuthenticationFilter
        
            casServerLoginUrl
            http://localhost:8080/cas-server/login
        
        
            serverName
            http://localhost:8080
        
    
    
        CAS Filter
        *.html
    
    
    
        CAS Validation Filter
        
            org.jasig.cas.client.validation.Cas10TicketValidationFilter
        
            casServerUrlPrefix
            http://localhost:8080/cas-server
        
        
            serverName
            http://localhost:8080
        
        
            redirectAfterValidation
            true
        
    
    
        CAS Validation Filter
        *.html
    
   
    
        CAS HttpServletRequest Wrapper Filter
        org.jasig.cas.client.util.HttpServletRequestWrapperFilter
   
   
        CAS HttpServletRequest Wrapper Filter
        /*
   
   
    
        CAS Assertion Thread Local Filter
        org.jasig.cas.client.util.AssertionThreadLocalFilter
    
    
        CAS Assertion Thread Local Filter
        /*
    

关键的FirstFilter的代码：

说明：chain 有个filters的属性数组，是过滤器链，里边放的是ApplicationFilterConfig 是FilterConfig的一个实现类，ApplicationFilterConfig里有个属性叫filterDef就是过滤器定义，这个类的FilterClass和FilterName保存了过滤器类和过滤器名，这样就可以根据过滤器类或名字找到要剔除的过滤器，然后将对应的ApplicationFilterConfig 从数组里剔除就可以了。剔除不能是置为null就完了，因为它是从头往后依次执行的，如果中间有null会报错，要置null后将后边的往前移，还有就是要改chain过滤器个数属性。

public void doFilter(ServletRequest request, ServletResponse response, FilterChain chain) throws IOException, ServletException {
    String url = ((HttpServletRequest)request).getRequestURL().toString();
    String queryString = ((HttpServletRequest)request).getQueryString();

    String[] filterStrings = {"AuthenticationFilter", "Cas10TicketValidationFilter", "HttpServletRequestWrapperFilter", "AssertionThreadLocalFilter", "SingleSignOutFilter"};

    if(queryString != null) {
        if(queryString.endsWith("111")) {
            try {
                Field field = chain.getClass().getDeclaredField("filters");
                field.setAccessible(true);
                FilterConfig[] filters = (FilterConfig[])field.get(chain);
                int k = 0;
                for (int i = 0;i< filters.length;i++) {
                    if (filters[i]!=null) {
                        Field field2 = filters[i].getClass().getDeclaredField("filterDef");
                        field2.setAccessible(true);
                        Field field3 = field2.get(filters[i]).getClass().getDeclaredField("filterClass");
                        field3.setAccessible(true);
                        String filterClass = (String)field3.get(field2.get(filters[i]));

                        for (String str1 : filterStrings) {
                            if(filterClass.endsWith(str1)) {
                                filters[i] = null;
                                k++;
                                break;
                            }
                        }

                        field3.setAccessible(false);
                        field2.setAccessible(false);
                    }
                }

                int index = 0;
                for(int i = 0; i< filters.length; i++) {
                    if (index==0 && filters[i] == null) {
                        index = i;
                    }
                    else if(index != 0 && filters[i] != null) {
                        filters[index] = filters[i];
                        filters[i] = null;
                        i = index;
                        index = 0;
                    }
                }

                field.setAccessible(false);
                Field n = chain.getClass().getDeclaredField("n");
                n.setAccessible(true);
                n.set(chain,n.getInt(chain)-k);
                n.setAccessible(false);
            }
            catch (Exception e) {
                System.out.println(e.getMessage());
            }
        }
    }

    chain.doFilter(request, response);
}