/*
* Copyright 2002-2008 the original author or authors.
*
* Licensed 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 org.springframework.web.filter;
import java.io.IOException;
import javax.servlet.Filter;
import javax.servlet.FilterChain;
import javax.servlet.ServletException;
import javax.servlet.ServletRequest;
import javax.servlet.ServletResponse;
import org.springframework.web.context.WebApplicationContext;
import org.springframework.web.context.support.WebApplicationContextUtils;
/**
* Proxy for a standard Servlet 2.3 Filter, delegating to a Spring-managed
* bean that implements the Filter interface. Supports a "targetBeanName"
* filter init-param in <code>web.xml</code>, specifying the name of the
* target bean in the Spring application context.
*
* <p><code>web.xml</code> will usually contain a DelegatingFilterProxy definition,
* with the specified <code>filter-name</code> corresponding to a bean name in
* Spring's root application context. All calls to the filter proxy will then
* be delegated to that bean in the Spring context, which is required to implement
* the standard Servlet 2.3 Filter interface.
*
* <p>This approach is particularly useful for Filter implementation with complex
* setup needs, allowing to apply the full Spring bean definition machinery to
* Filter instances. Alternatively, consider standard Filter setup in combination
* with looking up service beans from the Spring root application context.
*
* <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</code> and <code>Filter.destroy</code> lifecycle methods
* on the target bean, letting the servlet container manage the filter lifecycle.
*
* <p>This class is inspired by Acegi Security's FilterToBeanProxy class,
* written by Ben Alex.
*
* @author Juergen Hoeller
* @author Sam Brannen
* @since 1.2
* @see #setTargetBeanName
* @see #setTargetFilterLifecycle
* @see javax.servlet.Filter#doFilter
* @see javax.servlet.Filter#init
* @see javax.servlet.Filter#destroy
*/
public class DelegatingFilterProxy extends GenericFilterBean {
private String contextAttribute;
private String targetBeanName;
private boolean targetFilterLifecycle = false;
private Filter delegate;
private final Object delegateMonitor = new Object();
/**
* Set the name of the ServletContext attribute which should be used to retrieve the
* {@link WebApplicationContext} from which to load the delegate {@link Filter} bean.
*/
public void setContextAttribute(String contextAttribute) {
this.contextAttribute = contextAttribute;
}
/**
* Return the name of the ServletContext attribute which should be used to retrieve the
* {@link WebApplicationContext} from which to load the delegate {@link Filter} bean.
*/
public String getContextAttribute() {
return this.contextAttribute;
}
/**
* Set the name of the target bean in the Spring application context.
* The target bean must implement the standard Servlet 2.3 Filter interface.
* <p>By default, the <code>filter-name</code> as specified for the
* DelegatingFilterProxy in <code>web.xml</code> will be used.
*/
public void setTargetBeanName(String targetBeanName) {
this.targetBeanName = targetBeanName;
}
/**
* Return the name of the target bean in the Spring application context.
*/
protected String getTargetBeanName() {
return this.targetBeanName;
}
/**
* Set whether to invoke the <code>Filter.init</code> and
* <code>Filter.destroy</code> lifecycle methods on the target bean.
* <p>Default is "false"; target beans usually rely on the Spring application
* context for managing their lifecycle. Setting this flag to "true" means
* that the servlet container will control the lifecycle of the target
* Filter, with this proxy delegating the corresponding calls.
*/
public void setTargetFilterLifecycle(boolean targetFilterLifecycle) {
this.targetFilterLifecycle = targetFilterLifecycle;
}
/**
* Return whether to invoke the <code>Filter.init</code> and
* <code>Filter.destroy</code> lifecycle methods on the target bean.
*/
protected boolean isTargetFilterLifecycle() {
return this.targetFilterLifecycle;
}
protected void initFilterBean() throws ServletException {
// 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.
synchronized (this.delegateMonitor) {
WebApplicationContext wac = findWebApplicationContext();
if (wac != null) {
this.delegate = initDelegate(wac);
}
}
}
public void doFilter(ServletRequest request, ServletResponse response, FilterChain filterChain)
throws ServletException, IOException {
// Lazily initialize the delegate if necessary.
Filter delegateToUse = null;
synchronized (this.delegateMonitor) {
if (this.delegate == null) {
WebApplicationContext wac = findWebApplicationContext();
if (wac == null) {
throw new IllegalStateException("No WebApplicationContext found: no ContextLoaderListener registered?");
}
this.delegate = initDelegate(wac);
}
delegateToUse = this.delegate;
}
// Let the delegate perform the actual doFilter operation.
invokeDelegate(delegateToUse, request, response, filterChain);
}
public void destroy() {
Filter delegateToUse = null;
synchronized (this.delegateMonitor) {
delegateToUse = this.delegate;
}
if (delegateToUse != null) {
destroyDelegate(delegateToUse);
}
}
/**
* Retrieve a <code>WebApplicationContext</code> from the <code>ServletContext</code>
* attribute with the {@link #setContextAttribute configured name}. The
* <code>WebApplicationContext</code> must have already been loaded and stored in the
* <code>ServletContext</code> before this filter gets initialized (or invoked).
* <p>Subclasses may override this method to provide a different
* <code>WebApplicationContext</code> retrieval strategy.
* @return the WebApplicationContext for this proxy, or <code>null</code> if not found
* @see #getContextAttribute()
*/
protected WebApplicationContext findWebApplicationContext() {
String attrName = getContextAttribute();
if (attrName != null) {
return WebApplicationContextUtils.getWebApplicationContext(getServletContext(), attrName);
}
else {
return WebApplicationContextUtils.getWebApplicationContext(getServletContext());
}
}
/**
* Initialize the Filter delegate, defined as bean the given Spring
* application context.
* <p>Default implementation fetches the bean from the application context
* and calls the standard <code>Filter.init</code> method on it, passing
* in the FilterConfig of this Filter proxy.
* @param wac the root application context
* @return the initialized delegate Filter
* @throws ServletException if thrown by the Filter
* @see #getTargetBeanName()
* @see #isTargetFilterLifecycle()
* @see #getFilterConfig()
* @see javax.servlet.Filter#init(javax.servlet.FilterConfig)
*/
protected Filter initDelegate(WebApplicationContext wac) throws ServletException {
Filter delegate = (Filter) wac.getBean(getTargetBeanName(), Filter.class);
if (isTargetFilterLifecycle()) {
delegate.init(getFilterConfig());
}
return delegate;
}
/**
* Actually invoke the delegate Filter with the given request and response.
* @param delegate the delegate Filter
* @param request the current HTTP request
* @param response the current HTTP response
* @param filterChain the current FilterChain
* @throws ServletException if thrown by the Filter
* @throws IOException if thrown by the Filter
*/
protected void invokeDelegate(
Filter delegate, ServletRequest request, ServletResponse response, FilterChain filterChain)
throws ServletException, IOException {
delegate.doFilter(request, response, filterChain);
}
/**
* Destroy the Filter delegate.
* Default implementation simply calls <code>Filter.destroy</code> on it.
* @param delegate the Filter delegate (never <code>null</code>)
* @see #isTargetFilterLifecycle()
* @see javax.servlet.Filter#destroy()
*/
protected void destroyDelegate(Filter delegate) {
if (isTargetFilterLifecycle()) {
delegate.destroy();
}
}
}