org.springframework.beans.factory.config.ServiceLocatorFactoryBean 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.config;
import java.lang.reflect.Constructor;
import java.lang.reflect.InvocationHandler;
import java.lang.reflect.InvocationTargetException;
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.BeanFactoryUtils;
import org.springframework.beans.factory.FactoryBean;
import org.springframework.beans.factory.InitializingBean;
import org.springframework.beans.factory.ListableBeanFactory;
import org.springframework.util.StringUtils;
/**
* FactoryBean that takes an interface which must have one or more methods with
* the signatures MyType xxx() or MyType xxx(MyIdType id)
* (typically, MyService getService() or MyService getService(String id))
* and creates a dynamic proxy which implements that interface, delegating to the
* Spring BeanFactory underneath.
*
* Such service locator allow to decouple the caller from Spring BeanFactory API, using an
* appropriate custom locator interface. They will typically be used for prototype beans,
* 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,
* being able to invoke the locator's factory methods on demand. For singleton beans,
* direct setter or constructor injection of the target bean is preferable.
*
*
On invocation of the no-arg factory method, or the single-arg factory method with an id
* of null or empty String, if exactly one bean in the factory matches the return type of the
* factory method, that is returned, otherwise a NoSuchBeanDefinitionException is thrown.
*
*
On invocation of the single-arg factory method with a non-null (and non-empty) argument,
* the proxy returns the result of a BeanFactory.getBean(name) call, using a
* stringified version of the passed-in id as bean name.
*
*
A factory method argument will usually be a String, but can also be an int or a custom
* enumeration type, for example, stringified via toString. The resulting String
* can be used as bean name as-is, provided that corresponding beans are defined in the bean
* factory. Alternatively, mappings between service ids and bean names can be defined.
*
* @author Colin Sampaleanu
* @author Juergen Hoeller
* @since 1.1.4
* @see #setServiceLocatorInterface
* @see #setServiceMappings
*/
public class ServiceLocatorFactoryBean implements FactoryBean, BeanFactoryAware, InitializingBean {
private Class serviceLocatorInterface;
private Constructor serviceLocatorExceptionConstructor;
private Properties serviceMappings;
private ListableBeanFactory beanFactory;
private Object proxy;
/**
* Set the service locator interface to use, which must have one or more methods with
* the signatures MyType xxx() or MyType xxx(MyIdType id)
* (typically, MyService getService() or MyService getService(String id)).
* See class-level javadoc for information on the semantics of such methods.
*/
public void setServiceLocatorInterface(Class interfaceName) {
this.serviceLocatorInterface = interfaceName;
}
/**
* Set the exception class that the service locator should throw if service
* lookup failed. The specified exception class should have a constructor
* with one of the following parameter types: (String, Throwable)
* or (Throwable) or (String).
* 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(Class)
* @see #createServiceLocatorException(java.lang.reflect.Constructor, org.springframework.beans.BeansException)
* @see org.springframework.beans.BeansException
* @see org.springframework.beans.factory.NoSuchBeanDefinitionException
*/
public void setServiceLocatorExceptionClass(Class serviceLocatorExceptionClass) {
if (serviceLocatorExceptionClass != null && !Exception.class.isAssignableFrom(serviceLocatorExceptionClass)) {
throw new IllegalArgumentException(
"serviceLocatorException [" + serviceLocatorExceptionClass.getName() + "] is not a subclass of Exception");
}
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.
*
The empty string as service id key defines the mapping for 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;
}
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;
}
public void afterPropertiesSet() {
if (this.serviceLocatorInterface == null) {
throw new IllegalArgumentException("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.
*
The default implementation looks for a constructor with one of the
* following parameter types: (String, Throwable)
* or (Throwable) or (String).
* @param exceptionClass the exception class
* @return the constructor to use
* @see #setServiceLocatorExceptionClass
*/
protected Constructor determineServiceLocatorExceptionConstructor(Class exceptionClass) {
try {
return exceptionClass.getConstructor(new Class[] {String.class, Throwable.class});
}
catch (NoSuchMethodException ex) {
try {
return exceptionClass.getConstructor(new Class[] {Throwable.class});
}
catch (NoSuchMethodException ex2) {
try {
return exceptionClass.getConstructor(new Class[] {String.class});
}
catch (NoSuchMethodException ex3) {
throw new IllegalArgumentException(
"serviceLocatorException [" + 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.
*
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 exceptionConstructor, BeansException cause) {
Class[] paramTypes = exceptionConstructor.getParameterTypes();
Object[] args = new Object[paramTypes.length];
for (int i = 0; i < paramTypes.length; i++) {
if (paramTypes[i].equals(String.class)) {
args[i] = cause.getMessage();
}
else if (paramTypes[i].isInstance(cause)) {
args[i] = cause;
}
}
return (Exception) BeanUtils.instantiateClass(exceptionConstructor, args);
}
public Object getObject() {
return this.proxy;
}
public Class getObjectType() {
return this.serviceLocatorInterface;
}
public boolean isSingleton() {
return true;
}
/**
* Invocation handler that delegates service locator calls to the bean factory.
*/
private class ServiceLocatorInvocationHandler implements InvocationHandler {
public Object invoke(Object proxy, Method method, Object[] args) throws Throwable {
if (Object.class.equals(method.getDeclaringClass())) {
// It's normal to get here for non service locator interface method calls
// (toString, equals, etc). Simply apply call to invocation handler object.
try {
return method.invoke(this, args);
}
catch (InvocationTargetException invEx) {
throw invEx.getTargetException();
}
}
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.equals(serviceLocatorReturnType)) {
throw new UnsupportedOperationException(
"May only call methods with signature ' xxx()' or ' xxx( id)' " +
"on factory interface, but tried to call: " + interfaceMethod);
}
// Check whether a service id was passed in.
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;
}
}
try {
if (StringUtils.hasLength(beanName)) {
// Service locator for a specific bean name.
return beanFactory.getBean(beanName, serviceLocatorReturnType);
}
else {
// Service locator for a bean type.
return BeanFactoryUtils.beanOfTypeIncludingAncestors(beanFactory, serviceLocatorReturnType);
}
}
catch (BeansException ex) {
if (serviceLocatorExceptionConstructor != null) {
throw createServiceLocatorException(serviceLocatorExceptionConstructor, ex);
}
throw ex;
}
}
public String toString() {
return "Service locator: " + serviceLocatorInterface.getName();
}
}
}