Created
August 14, 2009 23:33
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/** | |
* Licensed to the Apache Software Foundation (ASF) under one or more | |
* contributor license agreements. See the NOTICE file distributed with | |
* this work for additional information regarding copyright ownership. | |
* The ASF licenses this file to You 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.apache.openejb.util; | |
import javax.interceptor.AroundInvoke; | |
import javax.interceptor.InvocationContext; | |
/** | |
* Propagates the InvocationContext so that anyone with access to | |
* the InvocationContext can see the caller's context and propogate | |
* state forward for the entire call stack. With this, no one with | |
* access to the InvocationContext should ever need a thread local. | |
* | |
* This is the one thread local to make all other thread locals unnecessary. | |
* | |
* This interceptor should be installed as a global interceptor and | |
* positioned to be the first interceptor executed. | |
* | |
* Anyone downstream of this interceptor can make a call like this | |
* to get access the an infinite amout of state up the stack. | |
* | |
* InvocationContext caller = (InvocationContext) invocationContext.getContextData().get("caller"); | |
* | |
* With the "caller" InvocationContext you can move specific state | |
* forward for quick access. | |
* | |
* // Move the fooState to the current InvocationContext | |
* Object state = caller.getContextData().get("fooState"); | |
* invocationContext.getContextData().put("fooState", oldContext); | |
* | |
* You can also look infinitely back the invocation chain for | |
* state set in a previous InvocationContext. | |
* | |
* Object fooState = null; | |
* for (InvocationContext context = invocationContext; | |
* fooState == null && context != null; | |
* context = (InvocationContext) context.getContextData().get("caller")) { | |
* | |
* fooState = context.getContextData().get("fooState"); | |
* } | |
* | |
* | |
* Same approach as above, but using a simple recursive method | |
* | |
* | |
* public Object get(InvocationContext context, String property) { | |
* if (context == null) return null; | |
* Map<String,Object> data = context.getContextData(); | |
* Object value = data.get(property); | |
* if (value != null) return value; | |
* return get((InvocationContext) data.get("caller"), property); | |
* } | |
* | |
* @author David Blevins | |
*/ | |
public class InvocationContextPropagator { | |
private final static ThreadLocal<InvocationContext> context = new ThreadLocal<InvocationContext>(); | |
@AroundInvoke | |
public Object intercept(InvocationContext newContext) throws Exception { | |
// Get the previous InvocationContext | |
InvocationContext oldContext = context.get(); | |
try { | |
// Now anyone can get the old context without the thread local | |
newContext.getContextData().put("caller", oldContext); | |
// Track the newContext for our purposes | |
context.set(newContext); | |
// Call the method | |
return newContext.proceed(); | |
} finally { | |
// restore the calling context | |
context.set(oldContext); | |
} | |
} | |
} |
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