/*
* Copyright 2002-2017 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.config;
import java.lang.reflect.Constructor;
import java.lang.reflect.InvocationHandler;
import java.lang.reflect.Method;
import java.lang.reflect.Proxy;
import java.util.Properties;
import org.springframework.beans.BeanUtils;
import org.springframework.beans.BeansException;
import org.springframework.beans.FatalBeanException;
import org.springframework.beans.factory.BeanFactory;
import org.springframework.beans.factory.BeanFactoryAware;
import org.springframework.beans.factory.FactoryBean;
import org.springframework.beans.factory.InitializingBean;
import org.springframework.beans.factory.ListableBeanFactory;
import org.springframework.lang.Nullable;
import org.springframework.util.Assert;
import org.springframework.util.ReflectionUtils;
import org.springframework.util.StringUtils;
/**
* A {@link FactoryBean} implementation that takes an interface which must have one or more
* methods with the signatures {@code MyType xxx()} or {@code MyType xxx(MyIdType id)}
* (typically, {@code MyService getService()} or {@code MyService getService(String id)})
* and creates a dynamic proxy which implements that interface, delegating to an
* underlying {@link org.springframework.beans.factory.BeanFactory}.
*
* <p>Such service locators permit the decoupling of calling code from
* the {@link org.springframework.beans.factory.BeanFactory} API, by using an
* appropriate custom locator interface. They will typically be used for
* <b>prototype beans</b>, i.e. for factory methods that are supposed to
* return a new instance for each call. The client receives a reference to the
* service locator via setter or constructor injection, to be able to invoke
* the locator's factory methods on demand. <b>For singleton beans, direct
* setter or constructor injection of the target bean is preferable.</b>
*
* <p>On invocation of the no-arg factory method, or the single-arg factory
* method with a String id of {@code null} or empty String, if exactly
* <b>one</b> bean in the factory matches the return type of the factory
* method, that bean is returned, otherwise a
* {@link org.springframework.beans.factory.NoSuchBeanDefinitionException}
* is thrown.
*
* <p>On invocation of the single-arg factory method with a non-null (and
* non-empty) argument, the proxy returns the result of a
* {@link org.springframework.beans.factory.BeanFactory#getBean(String)} call,
* using a stringified version of the passed-in id as bean name.
*
* <p>A factory method argument will usually be a String, but can also be an
* int or a custom enumeration type, for example, stringified via
* {@code toString}. The resulting String can be used as bean name as-is,
* provided that corresponding beans are defined in the bean factory.
* Alternatively, {@linkplain #setServiceMappings(java.util.Properties) a custom
* mapping} between service IDs and bean names can be defined.
*
* <p>By way of an example, consider the following service locator interface.
* Note that this interface is not dependent on any Spring APIs.
*
* <pre class="code">package a.b.c;
*
*public interface ServiceFactory {
*
* public MyService getService();
*}</pre>
*
* <p>A sample config in an XML-based
* {@link org.springframework.beans.factory.BeanFactory} might look as follows:
*
* <pre class="code"><beans>
*
* <!-- Prototype bean since we have state -->
* <bean id="myService" class="a.b.c.MyService" singleton="false"/>
*
* <!-- will lookup the above 'myService' bean by *TYPE* -->
* <bean id="myServiceFactory"
* class="org.springframework.beans.factory.config.ServiceLocatorFactoryBean">
* <property name="serviceLocatorInterface" value="a.b.c.ServiceFactory"/>
* </bean>
*
* <bean id="clientBean" class="a.b.c.MyClientBean">
* <property name="myServiceFactory" ref="myServiceFactory"/>
* </bean>
*
*</beans></pre>
*
* <p>The attendant {@code MyClientBean} class implementation might then
* look something like this:
*
* <pre class="code">package a.b.c;
*
*public class MyClientBean {
*
* private ServiceFactory myServiceFactory;
*
* // actual implementation provided by the Spring container
* public void setServiceFactory(ServiceFactory myServiceFactory) {
* this.myServiceFactory = myServiceFactory;
* }
*
* public void someBusinessMethod() {
* // get a 'fresh', brand new MyService instance
* MyService service = this.myServiceFactory.getService();
* // use the service object to effect the business logic...
* }
*}</pre>
*
* <p>By way of an example that looks up a bean <b>by name</b>, consider
* the following service locator interface. Again, note that this
* interface is not dependent on any Spring APIs.
*
* <pre class="code">package a.b.c;
*
*public interface ServiceFactory {
*
* public MyService getService (String serviceName);
*}</pre>
*
* <p>A sample config in an XML-based
* {@link org.springframework.beans.factory.BeanFactory} might look as follows:
*
* <pre class="code"><beans>
*
* <!-- Prototype beans since we have state (both extend MyService) -->
* <bean id="specialService" class="a.b.c.SpecialService" singleton="false"/>
* <bean id="anotherService" class="a.b.c.AnotherService" singleton="false"/>
*
* <bean id="myServiceFactory"
* class="org.springframework.beans.factory.config.ServiceLocatorFactoryBean">
* <property name="serviceLocatorInterface" value="a.b.c.ServiceFactory"/>
* </bean>
*
* <bean id="clientBean" class="a.b.c.MyClientBean">
* <property name="myServiceFactory" ref="myServiceFactory"/>
* </bean>
*
*</beans></pre>
*
* <p>The attendant {@code MyClientBean} class implementation might then
* look something like this:
*
* <pre class="code">package a.b.c;
*
*public class MyClientBean {
*
* private ServiceFactory myServiceFactory;
*
* // actual implementation provided by the Spring container
* public void setServiceFactory(ServiceFactory myServiceFactory) {
* this.myServiceFactory = myServiceFactory;
* }
*
* public void someBusinessMethod() {
* // get a 'fresh', brand new MyService instance
* MyService service = this.myServiceFactory.getService("specialService");
* // use the service object to effect the business logic...
* }
*
* public void anotherBusinessMethod() {
* // get a 'fresh', brand new MyService instance
* MyService service = this.myServiceFactory.getService("anotherService");
* // use the service object to effect the business logic...
* }
*}</pre>
*
* <p>See {@link ObjectFactoryCreatingFactoryBean} for an alternate approach.
*
* @author Colin Sampaleanu
* @author Juergen Hoeller
* @since 1.1.4
* @see #setServiceLocatorInterface
* @see #setServiceMappings
* @see ObjectFactoryCreatingFactoryBean
*/
public class ServiceLocatorFactoryBean implements FactoryBean<Object>, BeanFactoryAware, InitializingBean {
@Nullable
private Class<?> serviceLocatorInterface;
@Nullable
private Constructor<Exception> serviceLocatorExceptionConstructor;
@Nullable
private Properties serviceMappings;
@Nullable
private ListableBeanFactory beanFactory;
@Nullable
private Object proxy;
/**
* Set the service locator interface to use, which must have one or more methods with
* the signatures {@code MyType xxx()} or {@code MyType xxx(MyIdType id)}
* (typically, {@code MyService getService()} or {@code MyService getService(String id)}).
* See the {@link ServiceLocatorFactoryBean class-level Javadoc} for
* information on the semantics of such methods.
*/
public void setServiceLocatorInterface(Class<?> interfaceType) {
this.serviceLocatorInterface = interfaceType;
}
/**
* Set the exception class that the service locator should throw if service
* lookup failed. The specified exception class must have a constructor
* with one of the following parameter types: {@code (String, Throwable)}
* or {@code (Throwable)} or {@code (String)}.
* <p>If not specified, subclasses of Spring's BeansException will be thrown,
* for example NoSuchBeanDefinitionException. As those are unchecked, the
* caller does not need to handle them, so it might be acceptable that
* Spring exceptions get thrown as long as they are just handled generically.
* @see #determineServiceLocatorExceptionConstructor
* @see #createServiceLocatorException
*/
public void setServiceLocatorExceptionClass(Class<? extends Exception> serviceLocatorExceptionClass) {
this.serviceLocatorExceptionConstructor =
determineServiceLocatorExceptionConstructor(serviceLocatorExceptionClass);
}
/**
* Set mappings between service ids (passed into the service locator)
* and bean names (in the bean factory). Service ids that are not defined
* here will be treated as bean names as-is.
* <p>The empty string as service id key defines the mapping for {@code null} and
* empty string, and for factory methods without parameter. If not defined,
* a single matching bean will be retrieved from the bean factory.
* @param serviceMappings mappings between service ids and bean names,
* with service ids as keys as bean names as values
*/
public void setServiceMappings(Properties serviceMappings) {
this.serviceMappings = serviceMappings;
}
@Override
public void setBeanFactory(BeanFactory beanFactory) throws BeansException {
if (!(beanFactory instanceof ListableBeanFactory)) {
throw new FatalBeanException(
"ServiceLocatorFactoryBean needs to run in a BeanFactory that is a ListableBeanFactory");
}
this.beanFactory = (ListableBeanFactory) beanFactory;
}
@Override
public void afterPropertiesSet() {
if (this.serviceLocatorInterface == null) {
throw new IllegalArgumentException("Property 'serviceLocatorInterface' is required");
}
// Create service locator proxy.
this.proxy = Proxy.newProxyInstance(
this.serviceLocatorInterface.getClassLoader(),
new Class<?>[] {this.serviceLocatorInterface},
new ServiceLocatorInvocationHandler());
}
/**
* Determine the constructor to use for the given service locator exception
* class. Only called in case of a custom service locator exception.
* <p>The default implementation looks for a constructor with one of the
* following parameter types: {@code (String, Throwable)}
* or {@code (Throwable)} or {@code (String)}.
* @param exceptionClass the exception class
* @return the constructor to use
* @see #setServiceLocatorExceptionClass
*/
@SuppressWarnings("unchecked")
protected Constructor<Exception> determineServiceLocatorExceptionConstructor(Class<? extends Exception> exceptionClass) {
try {
return (Constructor<Exception>) exceptionClass.getConstructor(String.class, Throwable.class);
}
catch (NoSuchMethodException ex) {
try {
return (Constructor<Exception>) exceptionClass.getConstructor(Throwable.class);
}
catch (NoSuchMethodException ex2) {
try {
return (Constructor<Exception>) exceptionClass.getConstructor(String.class);
}
catch (NoSuchMethodException ex3) {
throw new IllegalArgumentException(
"Service locator exception [" + exceptionClass.getName() +
"] neither has a (String, Throwable) constructor nor a (String) constructor");
}
}
}
}
/**
* Create a service locator exception for the given cause.
* Only called in case of a custom service locator exception.
* <p>The default implementation can handle all variations of
* message and exception arguments.
* @param exceptionConstructor the constructor to use
* @param cause the cause of the service lookup failure
* @return the service locator exception to throw
* @see #setServiceLocatorExceptionClass
*/
protected Exception createServiceLocatorException(Constructor<Exception> exceptionConstructor, BeansException cause) {
Class<?>[] paramTypes = exceptionConstructor.getParameterTypes();
Object[] args = new Object[paramTypes.length];
for (int i = 0; i < paramTypes.length; i++) {
if (String.class == paramTypes[i]) {
args[i] = cause.getMessage();
}
else if (paramTypes[i].isInstance(cause)) {
args[i] = cause;
}
}
return BeanUtils.instantiateClass(exceptionConstructor, args);
}
@Override
@Nullable
public Object getObject() {
return this.proxy;
}
@Override
public Class<?> getObjectType() {
return this.serviceLocatorInterface;
}
@Override
public boolean isSingleton() {
return true;
}
/**
* Invocation handler that delegates service locator calls to the bean factory.
*/
private class ServiceLocatorInvocationHandler implements InvocationHandler {
@Override
public Object invoke(Object proxy, Method method, Object[] args) throws Throwable {
if (ReflectionUtils.isEqualsMethod(method)) {
// Only consider equal when proxies are identical.
return (proxy == args[0]);
}
else if (ReflectionUtils.isHashCodeMethod(method)) {
// Use hashCode of service locator proxy.
return System.identityHashCode(proxy);
}
else if (ReflectionUtils.isToStringMethod(method)) {
return "Service locator: " + serviceLocatorInterface;
}
else {
return invokeServiceLocatorMethod(method, args);
}
}
private Object invokeServiceLocatorMethod(Method method, Object[] args) throws Exception {
Class<?> serviceLocatorMethodReturnType = getServiceLocatorMethodReturnType(method);
try {
String beanName = tryGetBeanName(args);
Assert.state(beanFactory != null, "No BeanFactory available");
if (StringUtils.hasLength(beanName)) {
// Service locator for a specific bean name
return beanFactory.getBean(beanName, serviceLocatorMethodReturnType);
}
else {
// Service locator for a bean type
return beanFactory.getBean(serviceLocatorMethodReturnType);
}
}
catch (BeansException ex) {
if (serviceLocatorExceptionConstructor != null) {
throw createServiceLocatorException(serviceLocatorExceptionConstructor, ex);
}
throw ex;
}
}
/**
* Check whether a service id was passed in.
*/
private String tryGetBeanName(@Nullable Object[] args) {
String beanName = "";
if (args != null && args.length == 1 && args[0] != null) {
beanName = args[0].toString();
}
// Look for explicit serviceId-to-beanName mappings.
if (serviceMappings != null) {
String mappedName = serviceMappings.getProperty(beanName);
if (mappedName != null) {
beanName = mappedName;
}
}
return beanName;
}
private Class<?> getServiceLocatorMethodReturnType(Method method) throws NoSuchMethodException {
Assert.state(serviceLocatorInterface != null, "No service locator interface specified");
Class<?>[] paramTypes = method.getParameterTypes();
Method interfaceMethod = serviceLocatorInterface.getMethod(method.getName(), paramTypes);
Class<?> serviceLocatorReturnType = interfaceMethod.getReturnType();
// Check whether the method is a valid service locator.
if (paramTypes.length > 1 || void.class == serviceLocatorReturnType) {
throw new UnsupportedOperationException(
"May only call methods with signature '<type> xxx()' or '<type> xxx(<idtype> id)' " +
"on factory interface, but tried to call: " + interfaceMethod);
}
return serviceLocatorReturnType;
}
}
}
