/*
* Copyright 2002-2012 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.beans.factory.access;
import java.io.IOException;
import java.util.HashMap;
import java.util.Map;
import org.apache.commons.logging.Log;
import org.apache.commons.logging.LogFactory;
import org.springframework.beans.BeansException;
import org.springframework.beans.FatalBeanException;
import org.springframework.beans.factory.BeanDefinitionStoreException;
import org.springframework.beans.factory.BeanFactory;
import org.springframework.beans.factory.config.ConfigurableBeanFactory;
import org.springframework.beans.factory.config.ConfigurableListableBeanFactory;
import org.springframework.beans.factory.support.DefaultListableBeanFactory;
import org.springframework.beans.factory.xml.XmlBeanDefinitionReader;
import org.springframework.core.io.Resource;
import org.springframework.core.io.support.PathMatchingResourcePatternResolver;
import org.springframework.core.io.support.ResourcePatternResolver;
import org.springframework.core.io.support.ResourcePatternUtils;
/**
* <p>Keyed-singleton implementation of {@link BeanFactoryLocator},
* which accesses shared Spring {@link BeanFactory} instances.</p>
*
* <p>Please see the warning in BeanFactoryLocator's javadoc about appropriate usage
* of singleton style BeanFactoryLocator implementations. It is the opinion of the
* Spring team that the use of this class and similar classes is unnecessary except
* (sometimes) for a small amount of glue code. Excessive usage will lead to code
* that is more tightly coupled, and harder to modify or test.</p>
*
* <p>In this implementation, a BeanFactory is built up from one or more XML
* definition file fragments, accessed as resources. The default resource name
* searched for is 'classpath*:beanRefFactory.xml', with the Spring-standard
* 'classpath*:' prefix ensuring that if the classpath contains multiple copies
* of this file (perhaps one in each component jar) they will be combined. To
* override the default resource name, instead of using the no-arg
* {@link #getInstance()} method, use the {@link #getInstance(String selector)}
* variant, which will treat the 'selector' argument as the resource name to
* search for.</p>
*
* <p>The purpose of this 'outer' BeanFactory is to create and hold a copy of one
* or more 'inner' BeanFactory or ApplicationContext instances, and allow those
* to be obtained either directly or via an alias. As such, this class provides
* both singleton style access to one or more BeanFactories/ApplicationContexts,
* and also a level of indirection, allowing multiple pieces of code, which are
* not able to work in a Dependency Injection fashion, to refer to and use the
* same target BeanFactory/ApplicationContext instance(s), by different names.<p>
*
* <p>Consider an example application scenario:
*
* <ul>
* <li>{@code com.mycompany.myapp.util.applicationContext.xml} -
* ApplicationContext definition file which defines beans for 'util' layer.
* <li>{@code com.mycompany.myapp.dataaccess-applicationContext.xml} -
* ApplicationContext definition file which defines beans for 'data access' layer.
* Depends on the above.
* <li>{@code com.mycompany.myapp.services.applicationContext.xml} -
* ApplicationContext definition file which defines beans for 'services' layer.
* Depends on the above.
* </ul>
*
* <p>In an ideal scenario, these would be combined to create one ApplicationContext,
* or created as three hierarchical ApplicationContexts, by one piece of code
* somewhere at application startup (perhaps a Servlet filter), from which all other
* code in the application would flow, obtained as beans from the context(s). However
* when third party code enters into the picture, things can get problematic. If the
* third party code needs to create user classes, which should normally be obtained
* from a Spring BeanFactory/ApplicationContext, but can handle only newInstance()
* style object creation, then some extra work is required to actually access and
* use object from a BeanFactory/ApplicationContext. One solutions is to make the
* class created by the third party code be just a stub or proxy, which gets the
* real object from a BeanFactory/ApplicationContext, and delegates to it. However,
* it is is not normally workable for the stub to create the BeanFactory on each
* use, as depending on what is inside it, that can be an expensive operation.
* Additionally, there is a fairly tight coupling between the stub and the name of
* the definition resource for the BeanFactory/ApplicationContext. This is where
* SingletonBeanFactoryLocator comes in. The stub can obtain a
* SingletonBeanFactoryLocator instance, which is effectively a singleton, and
* ask it for an appropriate BeanFactory. A subsequent invocation (assuming the
* same class loader is involved) by the stub or another piece of code, will obtain
* the same instance. The simple aliasing mechanism allows the context to be asked
* for by a name which is appropriate for (or describes) the user. The deployer can
* match alias names to actual context names.
*
* <p>Another use of SingletonBeanFactoryLocator, is to demand-load/use one or more
* BeanFactories/ApplicationContexts. Because the definition can contain one of more
* BeanFactories/ApplicationContexts, which can be independent or in a hierarchy, if
* they are set to lazy-initialize, they will only be created when actually requested
* for use.
*
* <p>Given the above-mentioned three ApplicationContexts, consider the simplest
* SingletonBeanFactoryLocator usage scenario, where there is only one single
* {@code beanRefFactory.xml} definition file:
*
* <pre class="code"><?xml version="1.0" encoding="UTF-8"?>
* <!DOCTYPE beans PUBLIC "-//SPRING//DTD BEAN 2.0//EN" "http://www.springframework.org/dtd/spring-beans-2.0.dtd">
*
* <beans>
*
* <bean id="com.mycompany.myapp"
* class="org.springframework.context.support.ClassPathXmlApplicationContext">
* <constructor-arg>
* <list>
* <value>com/mycompany/myapp/util/applicationContext.xml</value>
* <value>com/mycompany/myapp/dataaccess/applicationContext.xml</value>
* <value>com/mycompany/myapp/dataaccess/services.xml</value>
* </list>
* </constructor-arg>
* </bean>
*
* </beans>
* </pre>
*
* The client code is as simple as:
*
* <pre class="code">
* BeanFactoryLocator bfl = SingletonBeanFactoryLocator.getInstance();
* BeanFactoryReference bf = bfl.useBeanFactory("com.mycompany.myapp");
* // now use some bean from factory
* MyClass zed = bf.getFactory().getBean("mybean");
* </pre>
*
* Another relatively simple variation of the {@code beanRefFactory.xml} definition file could be:
*
* <pre class="code"><?xml version="1.0" encoding="UTF-8"?>
* <!DOCTYPE beans PUBLIC "-//SPRING//DTD BEAN 2.0//EN" "http://www.springframework.org/dtd/spring-beans-2.0.dtd">
*
* <beans>
*
* <bean id="com.mycompany.myapp.util" lazy-init="true"
* class="org.springframework.context.support.ClassPathXmlApplicationContext">
* <constructor-arg>
* <value>com/mycompany/myapp/util/applicationContext.xml</value>
* </constructor-arg>
* </bean>
*
* <!-- child of above -->
* <bean id="com.mycompany.myapp.dataaccess" lazy-init="true"
* class="org.springframework.context.support.ClassPathXmlApplicationContext">
* <constructor-arg>
* <list><value>com/mycompany/myapp/dataaccess/applicationContext.xml</value></list>
* </constructor-arg>
* <constructor-arg>
* <ref bean="com.mycompany.myapp.util"/>
* </constructor-arg>
* </bean>
*
* <!-- child of above -->
* <bean id="com.mycompany.myapp.services" lazy-init="true"
* class="org.springframework.context.support.ClassPathXmlApplicationContext">
* <constructor-arg>
* <list><value>com/mycompany/myapp/dataaccess.services.xml</value></value>
* </constructor-arg>
* <constructor-arg>
* <ref bean="com.mycompany.myapp.dataaccess"/>
* </constructor-arg>
* </bean>
*
* <!-- define an alias -->
* <bean id="com.mycompany.myapp.mypackage"
* class="java.lang.String">
* <constructor-arg>
* <value>com.mycompany.myapp.services</value>
* </constructor-arg>
* </bean>
*
* </beans>
* </pre>
*
* <p>In this example, there is a hierarchy of three contexts created. The (potential)
* advantage is that if the lazy flag is set to true, a context will only be created
* if it's actually used. If there is some code that is only needed some of the time,
* this mechanism can save some resources. Additionally, an alias to the last context
* has been created. Aliases allow usage of the idiom where client code asks for a
* context with an id which represents the package or module the code is in, and the
* actual definition file(s) for the SingletonBeanFactoryLocator maps that id to
* a real context id.
*
* <p>A final example is more complex, with a {@code beanRefFactory.xml} for every module.
* All the files are automatically combined to create the final definition.
*
* <p>{@code beanRefFactory.xml} file inside jar for util module:
*
* <pre class="code"><?xml version="1.0" encoding="UTF-8"?>
* <!DOCTYPE beans PUBLIC "-//SPRING//DTD BEAN 2.0//EN" "http://www.springframework.org/dtd/spring-beans-2.0.dtd">
*
* <beans>
* <bean id="com.mycompany.myapp.util" lazy-init="true"
* class="org.springframework.context.support.ClassPathXmlApplicationContext">
* <constructor-arg>
* <value>com/mycompany/myapp/util/applicationContext.xml</value>
* </constructor-arg>
* </bean>
* </beans>
* </pre>
*
* {@code beanRefFactory.xml} file inside jar for data-access module:<br>
*
* <pre class="code"><?xml version="1.0" encoding="UTF-8"?>
* <!DOCTYPE beans PUBLIC "-//SPRING//DTD BEAN 2.0//EN" "http://www.springframework.org/dtd/spring-beans-2.0.dtd">
*
* <beans>
* <!-- child of util -->
* <bean id="com.mycompany.myapp.dataaccess" lazy-init="true"
* class="org.springframework.context.support.ClassPathXmlApplicationContext">
* <constructor-arg>
* <list><value>com/mycompany/myapp/dataaccess/applicationContext.xml</value></list>
* </constructor-arg>
* <constructor-arg>
* <ref bean="com.mycompany.myapp.util"/>
* </constructor-arg>
* </bean>
* </beans>
* </pre>
*
* {@code beanRefFactory.xml} file inside jar for services module:
*
* <pre class="code"><?xml version="1.0" encoding="UTF-8"?>
* <!DOCTYPE beans PUBLIC "-//SPRING//DTD BEAN 2.0//EN" "http://www.springframework.org/dtd/spring-beans-2.0.dtd">
*
* <beans>
* <!-- child of data-access -->
* <bean id="com.mycompany.myapp.services" lazy-init="true"
* class="org.springframework.context.support.ClassPathXmlApplicationContext">
* <constructor-arg>
* <list><value>com/mycompany/myapp/dataaccess/services.xml</value></list>
* </constructor-arg>
* <constructor-arg>
* <ref bean="com.mycompany.myapp.dataaccess"/>
* </constructor-arg>
* </bean>
* </beans>
* </pre>
*
* {@code beanRefFactory.xml} file inside jar for mypackage module. This doesn't
* create any of its own contexts, but allows the other ones to be referred to be
* a name known to this module:
*
* <pre class="code"><?xml version="1.0" encoding="UTF-8"?>
* <!DOCTYPE beans PUBLIC "-//SPRING//DTD BEAN 2.0//EN" "http://www.springframework.org/dtd/spring-beans-2.0.dtd">
*
* <beans>
* <!-- define an alias for "com.mycompany.myapp.services" -->
* <alias name="com.mycompany.myapp.services" alias="com.mycompany.myapp.mypackage"/>
* </beans>
* </pre>
*
* @author Colin Sampaleanu
* @author Juergen Hoeller
* @see org.springframework.context.access.ContextSingletonBeanFactoryLocator
* @see org.springframework.context.access.DefaultLocatorFactory
*/
public class SingletonBeanFactoryLocator implements BeanFactoryLocator {
private static final String DEFAULT_RESOURCE_LOCATION = "classpath*:beanRefFactory.xml";
protected static final Log logger = LogFactory.getLog(SingletonBeanFactoryLocator.class);
/** The keyed BeanFactory instances */
private static final Map<String, BeanFactoryLocator> instances = new HashMap<String, BeanFactoryLocator>();
/**
* Returns an instance which uses the default "classpath*:beanRefFactory.xml",
* as the name of the definition file(s). All resources returned by calling the
* current thread context ClassLoader's {@code getResources} method with
* this name will be combined to create a BeanFactory definition set.
* @return the corresponding BeanFactoryLocator instance
* @throws BeansException in case of factory loading failure
*/
public static BeanFactoryLocator getInstance() throws BeansException {
return getInstance(null);
}
/**
* Returns an instance which uses the the specified selector, as the name of the
* definition file(s). In the case of a name with a Spring 'classpath*:' prefix,
* or with no prefix, which is treated the same, the current thread context
* ClassLoader's {@code getResources} method will be called with this value
* to get all resources having that name. These resources will then be combined to
* form a definition. In the case where the name uses a Spring 'classpath:' prefix,
* or a standard URL prefix, then only one resource file will be loaded as the
* definition.
* @param selector the name of the resource(s) which will be read and
* combined to form the definition for the BeanFactoryLocator instance.
* Any such files must form a valid BeanFactory definition.
* @return the corresponding BeanFactoryLocator instance
* @throws BeansException in case of factory loading failure
*/
public static BeanFactoryLocator getInstance(String selector) throws BeansException {
String resourceLocation = selector;
if (resourceLocation == null) {
resourceLocation = DEFAULT_RESOURCE_LOCATION;
}
// For backwards compatibility, we prepend 'classpath*:' to the selector name if there
// is no other prefix (i.e. classpath*:, classpath:, or some URL prefix.
if (!ResourcePatternUtils.isUrl(resourceLocation)) {
resourceLocation = ResourcePatternResolver.CLASSPATH_ALL_URL_PREFIX + resourceLocation;
}
synchronized (instances) {
if (logger.isTraceEnabled()) {
logger.trace("SingletonBeanFactoryLocator.getInstance(): instances.hashCode=" +
instances.hashCode() + ", instances=" + instances);
}
BeanFactoryLocator bfl = instances.get(resourceLocation);
if (bfl == null) {
bfl = new SingletonBeanFactoryLocator(resourceLocation);
instances.put(resourceLocation, bfl);
}
return bfl;
}
}
// We map BeanFactoryGroup objects by String keys, and by the definition object.
private final Map<String, BeanFactoryGroup> bfgInstancesByKey = new HashMap<String, BeanFactoryGroup>();
private final Map<BeanFactory, BeanFactoryGroup> bfgInstancesByObj = new HashMap<BeanFactory, BeanFactoryGroup>();
private final String resourceLocation;
/**
* Constructor which uses the the specified name as the resource name
* of the definition file(s).
* @param resourceLocation the Spring resource location to use
* (either a URL or a "classpath:" / "classpath*:" pseudo URL)
*/
protected SingletonBeanFactoryLocator(String resourceLocation) {
this.resourceLocation = resourceLocation;
}
@Override
public BeanFactoryReference useBeanFactory(String factoryKey) throws BeansException {
synchronized (this.bfgInstancesByKey) {
BeanFactoryGroup bfg = this.bfgInstancesByKey.get(this.resourceLocation);
if (bfg != null) {
bfg.refCount++;
}
else {
// This group definition doesn't exist, we need to try to load it.
if (logger.isTraceEnabled()) {
logger.trace("Factory group with resource name [" + this.resourceLocation +
"] requested. Creating new instance.");
}
// Create the BeanFactory but don't initialize it.
BeanFactory groupContext = createDefinition(this.resourceLocation, factoryKey);
// Record its existence now, before instantiating any singletons.
bfg = new BeanFactoryGroup();
bfg.definition = groupContext;
bfg.refCount = 1;
this.bfgInstancesByKey.put(this.resourceLocation, bfg);
this.bfgInstancesByObj.put(groupContext, bfg);
// Now initialize the BeanFactory. This may cause a re-entrant invocation
// of this method, but since we've already added the BeanFactory to our
// mappings, the next time it will be found and simply have its
// reference count incremented.
try {
initializeDefinition(groupContext);
}
catch (BeansException ex) {
this.bfgInstancesByKey.remove(this.resourceLocation);
this.bfgInstancesByObj.remove(groupContext);
throw new BootstrapException("Unable to initialize group definition. " +
"Group resource name [" + this.resourceLocation + "], factory key [" + factoryKey + "]", ex);
}
}
try {
BeanFactory beanFactory;
if (factoryKey != null) {
beanFactory = bfg.definition.getBean(factoryKey, BeanFactory.class);
}
else {
beanFactory = bfg.definition.getBean(BeanFactory.class);
}
return new CountingBeanFactoryReference(beanFactory, bfg.definition);
}
catch (BeansException ex) {
throw new BootstrapException("Unable to return specified BeanFactory instance: factory key [" +
factoryKey + "], from group with resource name [" + this.resourceLocation + "]", ex);
}
}
}
/**
* Actually creates definition in the form of a BeanFactory, given a resource name
* which supports standard Spring resource prefixes ('classpath:', 'classpath*:', etc.)
* This is split out as a separate method so that subclasses can override the actual
* type used (to be an ApplicationContext, for example).
* <p>The default implementation simply builds a
* {@link org.springframework.beans.factory.support.DefaultListableBeanFactory}
* and populates it using an
* {@link org.springframework.beans.factory.xml.XmlBeanDefinitionReader}.
* <p>This method should not instantiate any singletons. That function is performed
* by {@link #initializeDefinition initializeDefinition()}, which should also be
* overridden if this method is.
* @param resourceLocation the resource location for this factory group
* @param factoryKey the bean name of the factory to obtain
* @return the corresponding BeanFactory reference
*/
protected BeanFactory createDefinition(String resourceLocation, String factoryKey) {
DefaultListableBeanFactory factory = new DefaultListableBeanFactory();
XmlBeanDefinitionReader reader = new XmlBeanDefinitionReader(factory);
ResourcePatternResolver resourcePatternResolver = new PathMatchingResourcePatternResolver();
try {
Resource[] configResources = resourcePatternResolver.getResources(resourceLocation);
if (configResources.length == 0) {
throw new FatalBeanException("Unable to find resource for specified definition. " +
"Group resource name [" + this.resourceLocation + "], factory key [" + factoryKey + "]");
}
reader.loadBeanDefinitions(configResources);
}
catch (IOException ex) {
throw new BeanDefinitionStoreException(
"Error accessing bean definition resource [" + this.resourceLocation + "]", ex);
}
catch (BeanDefinitionStoreException ex) {
throw new FatalBeanException("Unable to load group definition: " +
"group resource name [" + this.resourceLocation + "], factory key [" + factoryKey + "]", ex);
}
return factory;
}
/**
* Instantiate singletons and do any other normal initialization of the factory.
* Subclasses that override {@link #createDefinition createDefinition()} should
* also override this method.
* @param groupDef the factory returned by {@link #createDefinition createDefinition()}
*/
protected void initializeDefinition(BeanFactory groupDef) {
if (groupDef instanceof ConfigurableListableBeanFactory) {
((ConfigurableListableBeanFactory) groupDef).preInstantiateSingletons();
}
}
/**
* Destroy definition in separate method so subclass may work with other definition types.
* @param groupDef the factory returned by {@link #createDefinition createDefinition()}
* @param selector the resource location for this factory group
*/
protected void destroyDefinition(BeanFactory groupDef, String selector) {
if (groupDef instanceof ConfigurableBeanFactory) {
if (logger.isTraceEnabled()) {
logger.trace("Factory group with selector '" + selector +
"' being released, as there are no more references to it");
}
((ConfigurableBeanFactory) groupDef).destroySingletons();
}
}
/**
* We track BeanFactory instances with this class.
*/
private static class BeanFactoryGroup {
private BeanFactory definition;
private int refCount = 0;
}
/**
* BeanFactoryReference implementation for this locator.
*/
private class CountingBeanFactoryReference implements BeanFactoryReference {
private BeanFactory beanFactory;
private BeanFactory groupContextRef;
public CountingBeanFactoryReference(BeanFactory beanFactory, BeanFactory groupContext) {
this.beanFactory = beanFactory;
this.groupContextRef = groupContext;
}
@Override
public BeanFactory getFactory() {
return this.beanFactory;
}
// Note that it's legal to call release more than once!
@Override
public void release() throws FatalBeanException {
synchronized (bfgInstancesByKey) {
BeanFactory savedRef = this.groupContextRef;
if (savedRef != null) {
this.groupContextRef = null;
BeanFactoryGroup bfg = bfgInstancesByObj.get(savedRef);
if (bfg != null) {
bfg.refCount--;
if (bfg.refCount == 0) {
destroyDefinition(savedRef, resourceLocation);
bfgInstancesByKey.remove(resourceLocation);
bfgInstancesByObj.remove(savedRef);
}
}
else {
// This should be impossible.
logger.warn("Tried to release a SingletonBeanFactoryLocator group definition " +
"more times than it has actually been used. Resource name [" + resourceLocation + "]");
}
}
}
}
}
}
