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DefaultMethodHandler.java
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143 lines (129 loc) · 5.18 KB
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/**
* Copyright 2012-2021 The Feign 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 feign;
import feign.InvocationHandlerFactory.MethodHandler;
import java.lang.invoke.MethodHandle;
import java.lang.invoke.MethodHandles;
import java.lang.invoke.MethodHandles.Lookup;
import java.lang.reflect.Constructor;
import java.lang.reflect.Field;
import java.lang.reflect.InvocationTargetException;
import java.lang.reflect.Method;
/**
* Handles default methods by directly invoking the default method code on the interface. The bindTo
* method must be called on the result before invoke is called.
*/
final class DefaultMethodHandler implements MethodHandler {
// Uses Java 7 MethodHandle based reflection. As default methods will only exist when
// run on a Java 8 JVM this will not affect use on legacy JVMs.
// When Feign upgrades to Java 7, remove the @IgnoreJRERequirement annotation.
private final MethodHandle unboundHandle;
// handle is effectively final after bindTo has been called...
private MethodHandle handle;
public DefaultMethodHandler(Method defaultMethod) {
Class<?> declaringClass = defaultMethod.getDeclaringClass();
try {
Lookup lookup = readLookup(declaringClass);
this.unboundHandle = lookup.unreflectSpecial(defaultMethod, declaringClass);
} catch (NoSuchFieldException | IllegalAccessException | IllegalArgumentException
| InvocationTargetException ex) {
throw new IllegalStateException(ex);
}
}
private Lookup readLookup(Class<?> declaringClass)
throws IllegalAccessException, InvocationTargetException, NoSuchFieldException {
try {
return safeReadLookup(declaringClass);
} catch (NoSuchMethodException e) {
try {
return androidLookup(declaringClass);
} catch (InstantiationException | NoSuchMethodException instantiationException) {
return legacyReadLookup();
}
}
}
public Lookup androidLookup(Class<?> declaringClass) throws InstantiationException,
InvocationTargetException, NoSuchMethodException, IllegalAccessException {
Lookup lookup;
try {
// Android 9+ double reflection
Class<?> classReference = Class.class;
Class<?>[] classType = new Class[] {Class.class};
Method reflectedGetDeclaredConstructor = classReference.getDeclaredMethod(
"getDeclaredConstructor",
Class[].class);
reflectedGetDeclaredConstructor.setAccessible(true);
Constructor<?> someHiddenMethod =
(Constructor<?>) reflectedGetDeclaredConstructor.invoke(Lookup.class, (Object) classType);
lookup = (Lookup) someHiddenMethod.newInstance(declaringClass);
} catch (IllegalAccessException ex0) {
// Android < 9 reflection
Constructor<Lookup> lookupConstructor = Lookup.class.getDeclaredConstructor(Class.class);
lookupConstructor.setAccessible(true);
lookup = lookupConstructor.newInstance(declaringClass);
}
return (lookup);
}
/**
* equivalent to:
*
* <pre>
* return MethodHandles.privateLookupIn(declaringClass, MethodHandles.lookup());
* </pre>
*
* @param declaringClass
* @return
* @throws IllegalAccessException
* @throws InvocationTargetException
* @throws NoSuchMethodException
*/
private Lookup safeReadLookup(Class<?> declaringClass)
throws IllegalAccessException, InvocationTargetException, NoSuchMethodException {
Lookup lookup = MethodHandles.lookup();
Object privateLookupIn =
MethodHandles.class.getMethod("privateLookupIn", Class.class, Lookup.class)
.invoke(null, declaringClass, lookup);
return (Lookup) privateLookupIn;
}
private Lookup legacyReadLookup() throws NoSuchFieldException, IllegalAccessException {
Field field = Lookup.class.getDeclaredField("IMPL_LOOKUP");
field.setAccessible(true);
Lookup lookup = (Lookup) field.get(null);
return lookup;
}
/**
* Bind this handler to a proxy object. After bound, DefaultMethodHandler#invoke will act as if it
* was called on the proxy object. Must be called once and only once for a given instance of
* DefaultMethodHandler
*/
public void bindTo(Object proxy) {
if (handle != null) {
throw new IllegalStateException(
"Attempted to rebind a default method handler that was already bound");
}
handle = unboundHandle.bindTo(proxy);
}
/**
* Invoke this method. DefaultMethodHandler#bindTo must be called before the first time invoke is
* called.
*/
@Override
public Object invoke(Object[] argv) throws Throwable {
if (handle == null) {
throw new IllegalStateException(
"Default method handler invoked before proxy has been bound.");
}
return handle.invokeWithArguments(argv);
}
}