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jeremybenn |
/* CompositeDataInvocationHandler.java - Pseudo-accessors for CompositeData.
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Copyright (C) 2007 Free Software Foundation
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This file is part of GNU Classpath.
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GNU Classpath is free software; you can redistribute it and/or modify
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it under the terms of the GNU General Public License as published by
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the Free Software Foundation; either version 2, or (at your option)
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any later version.
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GNU Classpath is distributed in the hope that it will be useful, but
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WITHOUT ANY WARRANTY; without even the implied warranty of
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MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
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General Public License for more details.
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You should have received a copy of the GNU General Public License
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along with GNU Classpath; see the file COPYING. If not, write to the
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Free Software Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA
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02110-1301 USA.
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Linking this library statically or dynamically with other modules is
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making a combined work based on this library. Thus, the terms and
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conditions of the GNU General Public License cover the whole
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combination.
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As a special exception, the copyright holders of this library give you
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permission to link this library with independent modules to produce an
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executable, regardless of the license terms of these independent
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modules, and to copy and distribute the resulting executable under
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terms of your choice, provided that you also meet, for each linked
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independent module, the terms and conditions of the license of that
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module. An independent module is a module which is not derived from
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or based on this library. If you modify this library, you may extend
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this exception to your version of the library, but you are not
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obligated to do so. If you do not wish to do so, delete this
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exception statement from your version. */
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package javax.management.openmbean;
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import java.lang.reflect.InvocationHandler;
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import java.lang.reflect.Method;
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import java.lang.reflect.Proxy;
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/**
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* <p>
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* Provides an {@link java.lang.reflect.InvocationHandler} which
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* implements a series of accessor methods (those beginning with
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* {@code "get"} or {@code "is"}) using the content of a
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* {@link CompositeData} object. An instance of {@link CompositeData}
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* consists of a series of key-value mappings. This handler assumes
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* these keys to be the names of attributes, and thus provides
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* accessor methods by returning the associated value.
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* </p>
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* <p>
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* As an example, consider the following interface:
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* </p>
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* <pre>
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* public interface Person
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* {
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* public String getName();
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* public Date getBirthday();
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* }
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* </pre>
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* <p>
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* This specifies two accessor methods for retrieving the attributes,
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* {@code name} and {@code birthday}. An implementation of this interface
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* can be provided by creating an instance of this class, using a
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* {@link CompositeData} object with appropriate key-value mappings
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* (e.g. "name" => "Fred", "birthday" => 30/06/1974), and then passing
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* that to {@link java.lang.reflect.Proxy#newProxyInstance} along with
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* the interface itself. The invocation handler implements the methods
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* by calling {@link CompositeData#get(String)} with the appropriate key.
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* </p>
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* <p>
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* The attribute name is derived by taking the remainder of the method
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* name following {@code "get"}. If the first letter of this substring
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* is uppercase, then two attempts are made to retrieve the attribute
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* from the {@link CompositeData} instance: one using the original substring,
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* and one with the first letter changed to its lower-case equivalent.
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* If the first letter is lowercase, only the exact substring is used.
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* </p>
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* <p>
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* An {@link Object#equals(Object)} implementation is provided. This returns
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* true if the argument is a proxy with a {@link CompositeDataInvocationHandler}
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* using an equivalent {@link CompositeData} instance. {@link Object#hashCode()}
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* is also defined so as to match this implementation and give equivalent instances
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* the same hashcode.
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* </p>
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*
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* @author Andrew John Hughes (gnu_andrew@member.fsf.org)
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* @since 1.6
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*/
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public class CompositeDataInvocationHandler
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implements InvocationHandler
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{
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/**
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* The {@link CompositeData} providing the key-value mappings.
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*/
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private CompositeData data;
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/**
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* Constructs a new {@link CompositeDataInvocationHandler}
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* with the specified {@link CompositeData} instance.
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*
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* @param data the {@link CompositeData} instance to use.
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* @throws IllegalArgumentException if {@code data} is {@code null}.
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*/
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public CompositeDataInvocationHandler(CompositeData data)
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{
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if (data == null)
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throw new IllegalArgumentException("The CompositeData instance " +
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"must be non-null.");
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this.data = data;
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}
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/**
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* Returns the {@link CompositeData} instance which provides
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* the key-value mappings for this instance. This is never
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* {@code null}.
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*
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* @return the {@link CompositeData} instance.
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*/
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public CompositeData getCompositeData()
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{
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return data;
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}
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/**
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* Called by the proxy class whenever a method is called. The
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* handler only deals with accessor methods (beginning with
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* {@code "get"} or {@code "is"}), {@code equals}, and
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* {@code "hashCode"}. Accessor methods are implemented by
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* returning the appropriate value from the {@link CompositeData}
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* instance, while {@code equals} and {@code hashCode} allow
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* two proxies with a {@link CompositeDataInvocationHandler} using
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* the same {@link CompositeData} instance to be classified
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* as equivalent.
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*
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* @param proxy the proxy on which the method was called.
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* @param method the method which was called.
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* @param args the arguments supplied to the method.
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* @return the return value from the method.
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* @throws Throwable if an exception is thrown in the process.
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*/
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public Object invoke(Object proxy, Method method, Object[] args)
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throws Throwable
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{
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String mName = method.getName();
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if (mName.equals("equals"))
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{
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if (args[0] instanceof Proxy)
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{
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InvocationHandler h = Proxy.getInvocationHandler(args[0]);
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if (h instanceof CompositeDataInvocationHandler)
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return data.equals(((CompositeDataInvocationHandler)
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h).getCompositeData());
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}
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return false;
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}
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if (mName.equals("hashCode"))
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{
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return data.hashCode();
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}
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String attrib = null;
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if (mName.startsWith("get"))
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attrib = mName.substring(3);
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else if (mName.startsWith("is"))
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attrib = mName.substring(2);
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if (attrib == null)
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throw new NoSuchMethodException(mName + " is not an accessor.");
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if (!data.containsKey(attrib))
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{
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if (Character.isLowerCase(attrib.charAt(0)))
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throw new NoSuchMethodException("The attribute " +
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attrib + " is not available " +
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"in the given CompositeData " +
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"object");
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attrib = Character.toLowerCase(attrib.charAt(0))
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+ attrib.substring(1);
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if (!data.containsKey(attrib))
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throw new NoSuchMethodException("The attribute " +
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attrib + " is not available " +
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"in the given CompositeData " +
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"object");
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}
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return data.get(attrib);
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}
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}
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