org.wamblee.general.LookupProxyFactory Maven / Gradle / Ivy
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/*
* Copyright 2005-2010 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.wamblee.general;
import java.io.Serializable;
import java.lang.reflect.InvocationHandler;
import java.lang.reflect.InvocationTargetException;
import java.lang.reflect.Method;
import java.lang.reflect.Proxy;
import javax.naming.InitialContext;
import javax.naming.NamingException;
/**
* Proxy factory that can provide contextual references to objects retrieved
* through a lookup mechanism. The returned proxies are serializable.
*
* @param T
* Interface to proxy.
* @author Erik Brakkee
*
*/
public class LookupProxyFactory {
/**
* Interface to lookup the object to delegate to.
*
* @author Erik Brakkee
*/
public static interface Lookup extends Serializable {
/**
* Looks up the object.
*
* @return Object (non-null)
* @throws Any
* exception in case the object cannot be found.
*/
Object lookup() throws Exception;
}
/**
* Exception thrown in case an object cannot be retrieved from JNDI.
*
* @author Erik Brakkee
*/
public static class LookupException extends RuntimeException {
public LookupException(String aMsg, Throwable aCause) {
super(aMsg, aCause);
}
public LookupException(String aMsg) {
super(aMsg);
}
}
/**
* Invocation handler that does a lookup in JNDI and invokes the method on
* the object it found.
*
* @author Erik Brakkee
*/
private static class LookupInvocationHandler implements
InvocationHandler, Serializable {
private Class clazz;
private Lookup lookup;
/**
* Constructs the invocation handler.
*
* @param aLookup
* Lookup class.
*/
public LookupInvocationHandler(Class aClass, Lookup aLookup) {
clazz = aClass;
lookup = aLookup;
}
@Override
/**
* @throws JndiWiringException in case the object could not be retrieved from JNDI.
*/
public Object invoke(Object aProxy, Method aMethod, Object[] aArgs)
throws Throwable {
Object svcObj = null;
try {
svcObj = lookup.lookup();
} catch (Exception e) {
throw new LookupException("Error looking up object", e);
}
if (svcObj == null) {
throw new LookupException("Object is null");
}
if (!clazz.isInstance(svcObj)) {
throw new LookupException("Object '" + svcObj +
"' is not of type " + clazz.getName() + " but of type " +
svcObj.getClass().getName());
}
T svc = (T) svcObj;
try {
return aMethod.invoke(svc, aArgs);
} catch (InvocationTargetException e) {
throw e.getCause();
}
}
}
private Lookup lookup;
private Class clazz;
/**
* Constructs the factory.
*
* @param aClass
* Interface class of the service to proxy.
* @param aJndi
* JNDI name of the object to lookup.
*
*/
public LookupProxyFactory(Class aClass, Lookup aLookup) {
if (!aClass.isInterface()) {
throw new IllegalArgumentException("Class " + aClass.getName() +
" is not an interface");
}
clazz = aClass;
lookup = aLookup;
}
/**
* Gets the proxy that delegates to the instance obtained through the
* lookup interface.
*
* When at runtime the proxy cannot lookup the object, it
* throws {@link LookupException}.
*
* @return Proxy.
*/
public T getProxy() {
InvocationHandler handler = new LookupInvocationHandler(clazz, lookup);
Class proxyClass = Proxy.getProxyClass(clazz.getClassLoader(),
new Class[] { clazz });
T proxy;
try {
proxy = (T) proxyClass.getConstructor(
new Class[] { InvocationHandler.class }).newInstance(
new Object[] { handler });
return proxy;
} catch (Exception e) {
throw new RuntimeException("Could not create proxy for " +
clazz.getName(), e);
}
}
}