實現一個支援正則匹配的Filter以及Spring管理Filter遇到的問題
阿新 • • 發佈：2019-01-22
相信很多人都會對Http的Filter的url-pattern不支援正則而煩惱吧。就比如，在web專案中Struts，當我們想要對所有的或者某一個Action進行過濾，而不過濾其他的Action，尤其是不想過濾靜態資源，如果你的Struts配置了Action字尾可能會好一些，很可惜我的專案就沒有設定字尾，所有沒法使用url-pattern僅支援的幾種規則，所以就自己實現了一個抽象類，用來支援可配置需過濾以及不需過濾的url規則，且支援正則，具體原始碼可見下方。
原始碼其實很簡單，僅有基礎需要注意的地方：java的Matcher類是執行緒不安全的，所有在Filter中肯定是不能共享的，但是Pattern可以，所以我們將指定的規則初始化成Pattern快取起來，避免每次呼叫的時候都來初始化Pattern，提高效率；通過使用final修改方法以防止子類覆蓋doFilter的實現邏輯，並通過呼叫抽象方法innerDoFilter()來呼叫子類的過濾邏輯。import java.io.IOException; import java.util.regex.Pattern; 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; /** * <p> * 支援使用正則配置過濾指定URL * * web.xml配置時加入init-params: include:配置需要過濾的url規則，支援正則，多個之間已','分割 * exclude:配置不需要過濾的url規則，支援正則，多個之間已','分割 * </p> * * @author Vicky * @date 2015-5-13 */ public abstract class PatternFilter implements Filter { protected Pattern[] includePattern = null; protected Pattern[] excludePattern = null; public final void init(FilterConfig filterconfig) throws ServletException { String include = filterconfig.getInitParameter("include"); String exclude = filterconfig.getInitParameter("exclude"); if (null != include && !"".equals(include)) { String[] arr = include.split(","); includePattern = new Pattern[arr.length]; for (int i = 0; i < arr.length; i++) { includePattern[i] = Pattern.compile(arr[i]); } } if (null != exclude && !"".equals(exclude)) { String[] arr = exclude.split(","); excludePattern = new Pattern[arr.length]; for (int i = 0; i < arr.length; i++) { excludePattern[i] = Pattern.compile(arr[i]); } } innerInit(filterconfig); } /** * 子類進行初始化方法 * * @param filterconfig */ public abstract void innerInit(FilterConfig filterconfig) throws ServletException; public void destroy() { // TODO Auto-generated method stub } /** * filter過濾方法，final子類不可覆蓋，實現正則匹配規則，子類覆蓋innerDoFilter */ public final void doFilter(ServletRequest servletrequest, ServletResponse servletresponse, FilterChain filterchain) throws IOException, ServletException { String url = ((HttpServletRequest) servletrequest).getServletPath(); if (checkExclude(url) || !checkInclude(url)) {// 無需過濾該請求，則pass filterchain.doFilter(servletrequest, servletresponse); return; } // 呼叫innerDoFilter進行過濾 innerDoFilter(servletrequest, servletresponse, filterchain); return; } /** * 需子類覆蓋，實現過濾邏輯 * * @param servletrequest * @param servletresponse * @param filterchain */ public abstract void innerDoFilter(ServletRequest servletrequest, ServletResponse servletresponse, FilterChain filterchain) throws IOException, ServletException; /** * 檢驗訪問請求是否在include列表中 * * @param requestUrl * @return */ public final boolean checkInclude(String requestUrl) { boolean flag = true; if (null == includePattern || includePattern.length == 0) { return flag; } for (Pattern pat : includePattern) { if (flag = pat.matcher(requestUrl).matches()) break; } return flag; } /** * 檢驗訪問請求是否在exclude列表中 * * @param requestUrl * @return */ public final boolean checkExclude(String requestUrl) { boolean flag = false; if (null == excludePattern || excludePattern.length == 0) { return flag; } for (Pattern pat : excludePattern) { if (flag = pat.matcher(requestUrl).matches()) break; } return flag; } }
下面就來看看如何使用該過濾器。很簡單，首先寫一個Filter繼承自該類即可，實現innerDoFilter()以及innerInit()方法即可，然後在web.xml中新增該filter的配置，配置的時候就可以指定兩個init-param了，具體配置見下面。
從上面的配置檔案可以看見，添加了兩個初始化引數，含義配置中有詳細描述。不過我的配置可能跟普通的filter配置不同，是因為我使用了Spring來管理Filter，所以這裡的fliter-class是Spring的一個類(org.springframework.web.filter.DelegatingFilterProxy)，這個類預設會根據filter-name來查詢對應的bean來初始化成filter。下面說一下Spring的這個類DelegatingFilterProxy。filter> <filter-name>loginFilter</filter-name> <filter-class>org.springframework.web.filter.DelegatingFilterProxy</filter-class> <init-param> <description>指定Spring管理Filter生命週期</description> <param-name>targetFilterLifecycle</param-name> <param-value>true</param-value> </init-param> <init-param> <description>配置需要過濾的url規則，需使用正則，多個之間已','分割</description> <param-name>include</param-name> <param-value></param-value> </init-param> <init-param> <description>配置不需要過濾的url規則，需使用正則，多個之間已','分割</description> <param-name>exclude</param-name> <param-value>/css/.*,/js/.*,/images/.*,/fonts/.*,/plugin/.*</param-value> </init-param> </filter> <filter-mapping> <filter-name>loginFilter</filter-name> <url-pattern>/*</url-pattern> </filter-mapping>
從PatternFilter的程式碼可以看出需要呼叫init()方法，但是如果使用Spring的DelegatingFilterProxy類來管理Filter，預設情況下是不會呼叫Filter的init()方法的，這是因為預設情況下Spring是不會管理Filter的生命週期的，所以不會呼叫init()以及destory()方法。下面來簡單分析下DelegatingFilterProxy這個類的原始碼，看看哪裡是解決這個問題的關鍵。
首先開啟DelegatingFilterProxy類的原始碼，可以看出繼承自GenericFilterBean，而GenericFilterBean實現了Filter，並實現了init()方法。
public final void init(FilterConfig filterConfig) throws ServletException {
Assert.notNull(filterConfig, "FilterConfig must not be null");
if (logger.isDebugEnabled()) {
logger.debug("Initializing filter '" + filterConfig.getFilterName() + "'");
}
this.filterConfig = filterConfig;
// Set bean properties from init parameters.
try {
PropertyValues pvs = new FilterConfigPropertyValues(filterConfig, this.requiredProperties);
BeanWrapper bw = PropertyAccessorFactory.forBeanPropertyAccess(this);
ResourceLoader resourceLoader = new ServletContextResourceLoader(filterConfig.getServletContext());
bw.registerCustomEditor(Resource.class, new ResourceEditor(resourceLoader, this.environment));
initBeanWrapper(bw);
bw.setPropertyValues(pvs, true);
}
catch (BeansException ex) {
String msg = "Failed to set bean properties on filter '" +
filterConfig.getFilterName() + "': " + ex.getMessage();
logger.error(msg, ex);
throw new NestedServletException(msg, ex);
}
// Let subclasses do whatever initialization they like.
initFilterBean();
if (logger.isDebugEnabled()) {
logger.debug("Filter '" + filterConfig.getFilterName() + "' configured successfully");
}
}protected void initFilterBean() throws ServletException {
synchronized (this.delegateMonitor) {
if (this.delegate == null) {
// If no target bean name specified, use filter name.
if (this.targetBeanName == null) {
this.targetBeanName = getFilterName();
}
// Fetch Spring root application context and initialize the delegate early,
// if possible. If the root application context will be started after this
// filter proxy, we'll have to resort to lazy initialization.
WebApplicationContext wac = findWebApplicationContext();
if (wac != null) {
this.delegate = initDelegate(wac);
}
}
}
}protected Filter initDelegate(WebApplicationContext wac) throws ServletException {
Filter delegate = wac.getBean(getTargetBeanName(), Filter.class);
if (isTargetFilterLifecycle()) {
delegate.init(getFilterConfig());
}
return delegate;
}/**
* Return whether to invoke the {@code Filter.init} and
* {@code Filter.destroy} lifecycle methods on the target bean.
*/
protected boolean isTargetFilterLifecycle() {
return this.targetFilterLifecycle;
} * <p><b>NOTE:</b> The lifecycle methods defined by the Servlet Filter interface
* will by default <i>not</i> be delegated to the target bean, relying on the
* Spring application context to manage the lifecycle of that bean. Specifying
* the "targetFilterLifecycle" filter init-param as "true" will enforce invocation
* of the {@code Filter.init} and {@code Filter.destroy} lifecycle methods
* on the target bean, letting the servlet container manage the filter lifecycle.我們回到GenericFilterBean這個類的init()方法，可以看到其中有一個地方很想設定變數值的地方：bw.setPropertyValues(pvs, true);。結果深入看了下，就是這個地方設定的setTargetFilterLifecycle值，具體做法是獲取filter中所有的init-param引數，然後根據引數名通過反射獲取對應的set方法，並呼叫賦值，其中具體程式碼有很多不解之處，不過不影響理解這個問題。根據以上的邏輯，DelegatingFilterProxy類中的所有變數只有存在對應的set方法應該都是可以通過init-param指定。
以上就是我自己實現的可配置規則的Filter類以及Spring管理Filter遇到的問題。