org.springframework.beans.factory.access.SingletonBeanFactoryLocator Maven / Gradle / Ivy
/*
* Copyright 2002-2005 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;
/**
* Keyed-singleton implementation of BeanFactoryLocator, which leverages existing
* Spring constructs. This is normally accessed through DefaultLocatorFactory,
* but may also be used directly.
*
* 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.
*
* 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.
*
* 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.
*
*
Consider an example application scenario:
*
*
* com.mycompany.myapp.util.applicationContext.xml -
* ApplicationContext definition file which defines beans for 'util' layer.
* com.mycompany.myapp.dataaccess-applicationContext.xml -
* ApplicationContext definition file which defines beans for 'data access' layer.
* Depends on the above.
* com.mycompany.myapp.services.applicationContext.xml -
* ApplicationContext definition file which defines beans for 'services' layer.
* Depends on the above.
*
*
* 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.
*
*
Another use of SingletonBeanFactoryLocator, is to demand-load/use one or more
* BeanFactories/ApplicationContexts. Because the definiiton 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.
*
*
Given the above-mentioned three ApplicationContexts, consider the simplest
* SingletonBeanFactoryLocator usage scenario, where there is only one single
* beanRefFactory.xml definition file:
*
*
* <?xml version="1.0" encoding="UTF-8"?>
* <!DOCTYPE beans PUBLIC "-//SPRING//DTD BEAN//EN" "http://www.springframework.org/dtd/spring-beans.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>
*
*
* The client code is as simple as:
*
*
* BeanFactoryLocator bfl = SingletonBeanFactoryLocator.getInstance();
* BeanFactoryReference bf = bfl.useBeanFactory("com.mycompany.myapp");
* // now use some bean from factory
* MyClass zed = bf.getFactory().getBean("mybean");
*
*
* Another relatively simple variation of the beanRefFactory.xml definition file could be:
*
*
* <?xml version="1.0" encoding="UTF-8"?>
* <!DOCTYPE beans PUBLIC "-//SPRING//DTD BEAN//EN" "http://www.springframework.org/dtd/spring-beans.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>
*
*
* 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.
*
*
A final example is more complex, with a beanRefFactory.xml for every module.
* All the files are automatically combined to create the final definition.
*
*
beanRefFactory.xml file inside jar for util module:
*
*
* <?xml version="1.0" encoding="UTF-8"?>
* <!DOCTYPE beans PUBLIC "-//SPRING//DTD BEAN//EN" "http://www.springframework.org/dtd/spring-beans.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>
*
*
* beanRefFactory.xml file inside jar for data-access module:
*
*
* <?xml version="1.0" encoding="UTF-8"?>
* <!DOCTYPE beans PUBLIC "-//SPRING//DTD BEAN//EN" "http://www.springframework.org/dtd/spring-beans.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>
*
*
* beanRefFactory.xml file inside jar for services module:
*
*
* <?xml version="1.0" encoding="UTF-8"?>
* <!DOCTYPE beans PUBLIC "-//SPRING//DTD BEAN//EN" "http://www.springframework.org/dtd/spring-beans.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>
*
*
* 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:
*
*
* <?xml version="1.0" encoding="UTF-8"?>
* <!DOCTYPE beans PUBLIC "-//SPRING//DTD BEAN//EN" "http://www.springframework.org/dtd/spring-beans.dtd">
*
* <beans>
* <!-- define an alias for "com.mycompany.myapp.services" -->
* <alias name="com.mycompany.myapp.services" alias="com.mycompany.myapp.mypackage"/>
* </beans>
*
*
* @author Colin Sampaleanu
* @see org.springframework.context.access.DefaultLocatorFactory
*/
public class SingletonBeanFactoryLocator implements BeanFactoryLocator {
public static final String BEANS_REFS_XML_NAME = "classpath*:beanRefFactory.xml";
protected static final Log logger = LogFactory.getLog(SingletonBeanFactoryLocator.class);
// the keyed singleton instances
private static Map instances = new HashMap();
// We map BeanFactoryGroup objects by String keys, and by the definition object.
private final Map bfgInstancesByKey = new HashMap();
private final Map bfgInstancesByObj = new HashMap();
private final String resourceName;
/**
* 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's context classloader's getResources() method with this name
* will be combined to create a definition, which is just a BeanFactory.
*/
public static BeanFactoryLocator getInstance() throws FatalBeanException {
return getInstance(BEANS_REFS_XML_NAME);
}
/**
* 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's context
* classloader's 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 combine to
* form the definition for the SingletonBeanFactoryLocator instance. The one file
* or multiple fragments with this name must form a valid BeanFactory definition.
*/
public static BeanFactoryLocator getInstance(String selector) throws FatalBeanException {
// 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 (selector.indexOf(':') == -1) {
selector = ResourcePatternResolver.CLASSPATH_URL_PREFIX + selector;
}
synchronized (instances) {
if (logger.isDebugEnabled()) {
logger.debug("SingletonBeanFactoryLocator.getInstance(): instances.hashCode=" +
instances.hashCode() + ", instances=" + instances);
}
BeanFactoryLocator bfl = (BeanFactoryLocator) instances.get(selector);
if (bfl == null) {
bfl = new SingletonBeanFactoryLocator(selector);
instances.put(selector, bfl);
}
return bfl;
}
}
/**
* Constructor which uses the default "beanRefFactory.xml", as the name of the
* definition file(s). All resources returned by the definition classloader's
* getResources() method with this name will be combined to create a definition.
*/
protected SingletonBeanFactoryLocator() {
this.resourceName = BEANS_REFS_XML_NAME;
}
/**
* Constructor which uses the the specified name as the name of the
* definition file(s). All resources returned by the definition classloader's
* getResources() method with this name will be combined to create a definition
* definition.
*/
protected SingletonBeanFactoryLocator(String resourceName) {
this.resourceName = resourceName;
}
public BeanFactoryReference useBeanFactory(String factoryKey) throws BeansException {
synchronized (this.bfgInstancesByKey) {
BeanFactoryGroup bfg = (BeanFactoryGroup) this.bfgInstancesByKey.get(this.resourceName);
if (bfg != null) {
bfg.refCount++;
}
else {
// This group definition doesn't exist, we need to try to load it.
if (logger.isDebugEnabled()) {
logger.debug("Factory group with resource name [" + this.resourceName +
"] requested. Creating new instance.");
}
// Create the BeanFactory but don't initialize it.
BeanFactory groupContext = createDefinition(this.resourceName, factoryKey);
// Record its existence now, before instantiating any singletons.
bfg = new BeanFactoryGroup();
bfg.definition = groupContext;
bfg.refCount = 1;
this.bfgInstancesByKey.put(this.resourceName, 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) {
throw new BootstrapException("Unable to initialize group definition. " +
"Group resource name [" + this.resourceName + "], factory key [" + factoryKey + "]", ex);
}
}
final BeanFactory groupContext = bfg.definition;
String beanName = factoryKey;
Object bean;
try {
bean = groupContext.getBean(beanName);
if (bean instanceof String) {
logger.warn("You're using the deprecated alias-through-String-bean feature, " +
"which will be removed as of Spring 1.3. It is recommended to replace this " +
"with an tag (see SingletonBeanFactoryLocator javadoc).");
beanName = (String) bean;
bean = groupContext.getBean(beanName);
}
}
catch (BeansException ex) {
throw new BootstrapException("Unable to return specified BeanFactory instance: factory key [" +
factoryKey + "], from group with resource name [" + this.resourceName + "]", ex);
}
if (!(bean instanceof BeanFactory)) {
throw new BootstrapException("Bean '" + beanName + "' is not a BeanFactory: factory key [" +
factoryKey + "], from group with resource name [" + this.resourceName + "]");
}
final BeanFactory beanFactory = (BeanFactory) bean;
return new BeanFactoryReference() {
BeanFactory groupContextRef;
// constructor
{
this.groupContextRef = groupContext;
}
public BeanFactory getFactory() {
return beanFactory;
}
// Note that it's legal to call release more than once!
public void release() throws FatalBeanException {
synchronized (bfgInstancesByKey) {
BeanFactory savedRef = this.groupContextRef;
if (savedRef != null) {
this.groupContextRef = null;
BeanFactoryGroup bfg = (BeanFactoryGroup) bfgInstancesByObj.get(savedRef);
if (bfg != null) {
bfg.refCount--;
if (bfg.refCount == 0) {
destroyDefinition(savedRef, resourceName);
bfgInstancesByKey.remove(resourceName);
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 [" + resourceName + "]");
}
}
}
}
};
}
}
/**
* 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).
* This method should not instantiate any singletons. That function is performed
* by {@link #initializeDefinition initializeDefinition()}, which should also be
* overridden if this method is.
*/
protected BeanFactory createDefinition(String resourceName, String factoryKey) throws BeansException {
DefaultListableBeanFactory factory = new DefaultListableBeanFactory();
XmlBeanDefinitionReader reader = new XmlBeanDefinitionReader(factory);
ResourcePatternResolver resourcePatternResolver = new PathMatchingResourcePatternResolver();
try {
Resource[] configResources = resourcePatternResolver.getResources(resourceName);
if (configResources.length == 0) {
throw new FatalBeanException("Unable to find resource for specified definition. " +
"Group resource name [" + this.resourceName + "], factory key [" + factoryKey + "]");
}
reader.loadBeanDefinitions(configResources);
}
catch (IOException ex) {
throw new BeanDefinitionStoreException(
"Error accessing bean definition resource [" + this.resourceName + "]", ex);
}
catch (BeanDefinitionStoreException ex) {
throw new FatalBeanException("Unable to load group definition: " +
"group resource name [" + this.resourceName + "], 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) throws BeansException {
if (groupDef instanceof ConfigurableListableBeanFactory) {
((ConfigurableListableBeanFactory) groupDef).preInstantiateSingletons();
}
}
/**
* Destroy definition in separate method so subclass may work with other definition types.
*/
protected void destroyDefinition(BeanFactory groupDef, String resourceName) throws BeansException {
if (groupDef instanceof ConfigurableBeanFactory) {
// debugging trace only
if (logger.isDebugEnabled()) {
logger.debug("Factory group with resource name '" + resourceName +
"' 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;
}
}