adding servlet api (from tomcat)

[gigi.git] / lib / servlet-api / javax / servlet / Filter.java

diff --git a/lib/servlet-api/javax/servlet/Filter.java b/lib/servlet-api/javax/servlet/Filter.java
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+/*
+ * Licensed to the Apache Software Foundation (ASF) under one or more
+ * contributor license agreements.  See the NOTICE file distributed with
+ * this work for additional information regarding copyright ownership.
+ * The ASF licenses this file to You under the Apache License, Version 2.0
+ * (the "License"); you may not use this file except in compliance with
+ * the License.  You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+package javax.servlet;
+
+import java.io.IOException;
+
+/**
+ * A filter is an object that performs filtering tasks on either the request to
+ * a resource (a servlet or static content), or on the response from a resource,
+ * or both. <br>
+ * <br>
+ * Filters perform filtering in the <code>doFilter</code> method. Every Filter
+ * has access to a FilterConfig object from which it can obtain its
+ * initialization parameters, a reference to the ServletContext which it can
+ * use, for example, to load resources needed for filtering tasks.
+ * <p>
+ * Filters are configured in the deployment descriptor of a web application
+ * <p>
+ * Examples that have been identified for this design are<br>
+ * 1) Authentication Filters <br>
+ * 2) Logging and Auditing Filters <br>
+ * 3) Image conversion Filters <br>
+ * 4) Data compression Filters <br>
+ * 5) Encryption Filters <br>
+ * 6) Tokenizing Filters <br>
+ * 7) Filters that trigger resource access events <br>
+ * 8) XSL/T filters <br>
+ * 9) Mime-type chain Filter <br>
+ *
+ * @since Servlet 2.3
+ */
+public interface Filter {
+
+    /**
+     * Called by the web container to indicate to a filter that it is being
+     * placed into service. The servlet container calls the init method exactly
+     * once after instantiating the filter. The init method must complete
+     * successfully before the filter is asked to do any filtering work. <br>
+     * <br>
+     * The web container cannot place the filter into service if the init method
+     * either<br>
+     * 1.Throws a ServletException <br>
+     * 2.Does not return within a time period defined by the web container
+     */
+    public void init(FilterConfig filterConfig) throws ServletException;
+
+    /**
+     * The <code>doFilter</code> method of the Filter is called by the container
+     * each time a request/response pair is passed through the chain due to a
+     * client request for a resource at the end of the chain. The FilterChain
+     * passed in to this method allows the Filter to pass on the request and
+     * response to the next entity in the chain.
+     * <p>
+     * A typical implementation of this method would follow the following
+     * pattern:- <br>
+     * 1. Examine the request<br>
+     * 2. Optionally wrap the request object with a custom implementation to
+     * filter content or headers for input filtering <br>
+     * 3. Optionally wrap the response object with a custom implementation to
+     * filter content or headers for output filtering <br>
+     * 4. a) <strong>Either</strong> invoke the next entity in the chain using
+     * the FilterChain object (<code>chain.doFilter()</code>), <br>
+     * 4. b) <strong>or</strong> not pass on the request/response pair to the
+     * next entity in the filter chain to block the request processing<br>
+     * 5. Directly set headers on the response after invocation of the next
+     * entity in the filter chain.
+     **/
+    public void doFilter(ServletRequest request, ServletResponse response,
+            FilterChain chain) throws IOException, ServletException;
+
+    /**
+     * Called by the web container to indicate to a filter that it is being
+     * taken out of service. This method is only called once all threads within
+     * the filter's doFilter method have exited or after a timeout period has
+     * passed. After the web container calls this method, it will not call the
+     * doFilter method again on this instance of the filter. <br>
+     * <br>
+     *
+     * This method gives the filter an opportunity to clean up any resources
+     * that are being held (for example, memory, file handles, threads) and make
+     * sure that any persistent state is synchronized with the filter's current
+     * state in memory.
+     */
+    public void destroy();
+
+}