/*
* @(#)CompositeDataInvocationHandler.java 1.6 05/11/17
*
* Copyright 2006 Sun Microsystems, Inc. All rights reserved.
* SUN PROPRIETARY/CONFIDENTIAL. Use is subject to license terms.
*/
package javax.management.openmbean;
import com.sun.jmx.mbeanserver.MXBeanLookup;
import com.sun.jmx.mbeanserver.OpenConverter;
import java.lang.reflect.InvocationHandler;
import java.lang.reflect.Method;
import java.lang.reflect.Proxy;
/**
<p>An {@link InvocationHandler} that forwards getter methods to a
{@link CompositeData}. If you have an interface that contains
only getter methods (such as {@code String getName()} or
{@code boolean isActive()}) then you can use this class in
conjunction with the {@link Proxy} class to produce an implementation
of the interface where each getter returns the value of the
corresponding item in a {@code CompositeData}.</p>
<p>For example, suppose you have an interface like this:
<blockquote>
<pre>
public interface NamedNumber {
public int getNumber();
public String getName();
}
</pre>
</blockquote>
and a {@code CompositeData} constructed like this:
<blockquote>
<pre>
CompositeData cd =
new {@link CompositeDataSupport}(
someCompositeType,
new String[] {"number", "name"},
new Object[] {<b>5</b>, "five"}
);
</pre>
</blockquote>
then you can construct an object implementing {@code NamedNumber}
and backed by the object {@code cd} like this:
<blockquote>
<pre>
InvocationHandler handler =
new CompositeDataInvocationHandler(cd);
NamedNumber nn = (NamedNumber)
Proxy.newProxyInstance(NamedNumber.class.getClassLoader(),
new Class[] {NamedNumber.class},
handler);
</pre>
</blockquote>
A call to {@code nn.getNumber()} will then return <b>5</b>.</p>
<p>If the first letter of the property defined by a getter is a
capital, then this handler will look first for an item in the
{@code CompositeData} beginning with a capital, then, if that is
not found, for an item beginning with the corresponding lowercase
letter or code point. For a getter called {@code getNumber()}, the
handler will first look for an item called {@code Number}, then for
{@code number}. If the getter is called {@code getnumber()}, then
the item must be called {@code number}.</p>
<p>If the method given to {@link #invoke invoke} is the method
{@code boolean equals(Object)} inherited from {@code Object}, then
it will return true if and only if the argument is a {@code Proxy}
whose {@code InvocationHandler} is also a {@code
CompositeDataInvocationHandler} and whose backing {@code
CompositeData} is equal (not necessarily identical) to this
object's. If the method given to {@code invoke} is the method
{@code int hashCode()} inherited from {@code Object}, then it will
return a value that is consistent with this definition of {@code
equals}: if two objects are equal according to {@code equals}, then
they will have the same {@code hashCode}.</p>
@since 1.6
*/
public class CompositeDataInvocationHandler implements InvocationHandler {
/**
<p>Construct a handler backed by the given {@code
CompositeData}.</p>
@param compositeData the {@code CompositeData} that will supply
information to getters.
@throws IllegalArgumentException if {@code compositeData}
is null.
*/
public CompositeDataInvocationHandler(CompositeData compositeData) {
this(compositeData, null);
}
/**
<p>Construct a handler backed by the given {@code
CompositeData}.</p>
@param mbsc the {@code MBeanServerConnection} related to this
{@code CompositeData}. This is only relevant if a method in
the interface for which this is an invocation handler returns
a type that is an MXBean interface. Otherwise, it can be null.
@param compositeData the {@code CompositeData} that will supply
information to getters.
@throws IllegalArgumentException if {@code compositeData}
is null.
*/
CompositeDataInvocationHandler(CompositeData compositeData,
MXBeanLookup lookup) {
if (compositeData == null)
throw new IllegalArgumentException("compositeData");
this.compositeData = compositeData;
this.lookup = lookup;
}
/**
Return the {@code CompositeData} that was supplied to the
constructor.
@return the {@code CompositeData} that this handler is backed
by. This is never null.
*/
public CompositeData getCompositeData() {
assert compositeData != null;
return compositeData;
}
public Object invoke(Object proxy, Method method, Object[] args)
throws Throwable {
final String methodName = method.getName();
// Handle the methods from java.lang.Object
if (method.getDeclaringClass() == Object.class) {
if (methodName.equals("toString") && args == null)
return "Proxy[" + compositeData + "]";
else if (methodName.equals("hashCode") && args == null)
return compositeData.hashCode() + 0x43444948;
else if (methodName.equals("equals") && args.length == 1
&& method.getParameterTypes()[0] == Object.class)
return equals(proxy, args[0]);
else {
/* Either someone is calling invoke by hand, or
it is a non-final method from Object overriden
by the generated Proxy. At the time of writing,
the only non-final methods in Object that are not
handled above are finalize and clone, and these
are not overridden in generated proxies. */
return method.invoke(this, args);
}
}
String propertyName = OpenConverter.propertyName(method);
if (propertyName == null) {
throw new IllegalArgumentException("Method is not getter: " +
method.getName());
}
Object openValue;
if (compositeData.containsKey(propertyName))
openValue = compositeData.get(propertyName);
else {
String decap = OpenConverter.decapitalize(propertyName);
if (compositeData.containsKey(decap))
openValue = compositeData.get(decap);
else {
final String msg =
"No CompositeData item " + propertyName +
(decap.equals(propertyName) ? "" : " or " + decap) +
" to match " + methodName;
throw new IllegalArgumentException(msg);
}
}
OpenConverter converter =
OpenConverter.toConverter(method.getGenericReturnType());
return converter.fromOpenValue(lookup, openValue);
}
/* This method is called when equals(Object) is
* called on our proxy and hence forwarded to us. For example, if we
* are a proxy for an interface like this:
* public interface GetString {
* public String string();
* }
* then we must compare equal to another CompositeDataInvocationHandler
* proxy for the same interface and where string() returns the same value.
*
* You might think that we should also compare equal to another
* object that implements GetString directly rather than using
* Proxy, provided that its string() returns the same result as
* ours, and in fact an earlier version of this class did that (by
* converting the other object into a CompositeData and comparing
* that with ours). But in fact that doesn't make a great deal of
* sense because there's absolutely no guarantee that the
* resulting equals would be reflexive (otherObject.equals(this)
* might be false even if this.equals(otherObject) is true), and,
* especially, there's no way we could generate a hashCode() that
* would be equal to otherObject.hashCode() when
* this.equals(otherObject), because we don't know how
* otherObject.hashCode() is computed.
*/
private boolean equals(Object proxy, Object other) {
if (other == null)
return false;
final Class proxyClass = proxy.getClass();
final Class otherClass = other.getClass();
if (proxyClass != otherClass)
return false;
InvocationHandler otherih = Proxy.getInvocationHandler(other);
if (!(otherih instanceof CompositeDataInvocationHandler))
return false;
CompositeDataInvocationHandler othercdih =
(CompositeDataInvocationHandler) otherih;
return compositeData.equals(othercdih.compositeData);
}
private final CompositeData compositeData;
private final MXBeanLookup lookup;
}