/**
* Copyright 2014 Development Sprint, LLC.
*
* 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 com.developmentsprint.spring.breaker.annotations;
import java.lang.reflect.Method;
import java.lang.reflect.Modifier;
import java.util.Map;
import java.util.concurrent.ConcurrentHashMap;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;
import org.springframework.core.BridgeMethodResolver;
import org.springframework.util.ClassUtils;
import org.springframework.util.ObjectUtils;
import com.developmentsprint.spring.breaker.interceptor.CircuitBreakerAttribute;
import com.developmentsprint.spring.breaker.interceptor.CircuitBreakerAttributeSource;
import com.developmentsprint.spring.breaker.interceptor.DefaultCircuitBreakerAttribute;
/**
* Abstract implementation of {@link CircuitBreakerAttributeSource} that caches attributes for methods and implements a fallback policy:
* <ol>
* <li>specific target method
* <li>target class
* <li>declaring method
* <li>declaring class/interface.
* </ol>
*
* <p>
* Defaults to using the target class's circuit breaker attribute if none is associated with the target method. Any circuit breaker attribute associated with
* the target method completely overrides a class circuit breaker attribute. If none found on the target class, the interface that the invoked method has been
* called through (in case of a JDK proxy) will be checked.
*
* <p>
* This implementation caches attributes by method after they are first used. If it is ever desirable to allow dynamic changing of circuit breaker attributes
* (which is very unlikely), caching could be made configurable.
*
* @author Todd Orr
* @since 1.0
*/
abstract class AbstractFallbackCircuitBreakerAttributeSource implements CircuitBreakerAttributeSource {
/**
* Canonical value held in cache to indicate no circuit breaker attribute was found for this method, and we don't need to look again.
*/
private final static CircuitBreakerAttribute NULL_CIRCUIT_BREAKER_ATTRIBUTE = new DefaultCircuitBreakerAttribute();
/**
* Logger available to subclasses.
* <p>
* As this base class is not marked Serializable, the logger will be recreated after serialization - provided that the concrete subclass is Serializable.
*/
protected final Logger log = LoggerFactory.getLogger(getClass());
/**
* Cache of {@link CircuitBreakerAttribute}s, keyed by DefaultCacheKey (Method + target Class).
* <p>
* As this base class is not marked Serializable, the cache will be recreated after serialization - provided that the concrete subclass is Serializable.
*/
final Map<Object, CircuitBreakerAttribute> attributeCache = new ConcurrentHashMap<Object, CircuitBreakerAttribute>(1024);
/**
* Determine the circuit breaker attribute for this method invocation.
* <p>
* Defaults to the class's circuit breaker attribute if no method attribute is found.
*
* @param method
* the method for the current invocation (never {@code null})
* @param targetClass
* the target class for this invocation (may be {@code null})
* @return CircuitBreakerAttribute for this method, or {@code null} if the method is not wrapped in a circuit breaker
*/
public CircuitBreakerAttribute getCircuitBreakerAttribute(Method method, Class<?> targetClass) {
// First, see if we have a cached value.
Object cacheKey = getCacheKey(method, targetClass);
Object cached = this.attributeCache.get(cacheKey);
if (cached != null) {
// Value will either be canonical value indicating there is no circuit breaker attribute,
// or an actual circuit breaker attribute.
if (cached == NULL_CIRCUIT_BREAKER_ATTRIBUTE) {
return null;
}
else {
return (CircuitBreakerAttribute) cached;
}
}
else {
// We need to work it out.
CircuitBreakerAttribute cbAttribute = computeCircuitBreakerAttribute(method, targetClass);
// Put it in the cache.
if (cbAttribute == null) {
this.attributeCache.put(cacheKey, NULL_CIRCUIT_BREAKER_ATTRIBUTE);
}
else {
if (log.isDebugEnabled()) {
Class<?> classToLog = (targetClass != null ? targetClass : method.getDeclaringClass());
log.debug("Adding circuit breaker method '{}.{}' with attribute: {}", classToLog.getSimpleName(), method.getName(), cbAttribute);
}
this.attributeCache.put(cacheKey, cbAttribute);
}
return cbAttribute;
}
}
/**
* Determine a cache key for the given method and target class.
* <p>
* Must not produce same key for overloaded methods. Must produce same key for different instances of the same method.
*
* @param method
* the method (never {@code null})
* @param targetClass
* the target class (may be {@code null})
* @return the cache key (never {@code null})
*/
protected Object getCacheKey(Method method, Class<?> targetClass) {
return new DefaultCacheKey(method, targetClass);
}
/**
* Same signature as {@link #getCircuitBreakerAttribute}, but doesn't cache the result. {@link #getCircuitBreakerAttribute} is effectively a caching
* decorator for this method.
*
* @see #getCircuitBreakerAttribute(Method, Class)
*/
private CircuitBreakerAttribute computeCircuitBreakerAttribute(Method method, Class<?> targetClass) {
// Don't allow no-public methods as required.
if (allowPublicMethodsOnly() && !Modifier.isPublic(method.getModifiers())) {
return null;
}
// Ignore CGLIB subclasses - introspect the actual user class.
Class<?> userClass = ClassUtils.getUserClass(targetClass);
// The method may be on an interface, but we need attributes from the target class.
// If the target class is null, the method will be unchanged.
Method specificMethod = ClassUtils.getMostSpecificMethod(method, userClass);
// If we are dealing with method with generic parameters, find the original method.
specificMethod = BridgeMethodResolver.findBridgedMethod(specificMethod);
// First try is the method in the target class.
CircuitBreakerAttribute cbAttribute = findCircuitBreakerAttribute(specificMethod);
if (cbAttribute != null) {
return cbAttribute;
}
// Second try is the circuit breaker attribute on the target class.
cbAttribute = findCircuitBreakerAttribute(specificMethod.getDeclaringClass());
if (cbAttribute != null) {
return cbAttribute;
}
if (specificMethod != method) {
// Fallback is to look at the original method.
cbAttribute = findCircuitBreakerAttribute(method);
if (cbAttribute != null) {
return cbAttribute;
}
// Last fallback is the class of the original method.
return findCircuitBreakerAttribute(method.getDeclaringClass());
}
return null;
}
/**
* Subclasses need to implement this to return the circuit breaker attribute for the given method, if any.
*
* @param method
* the method to retrieve the attribute for
* @return all circuit breaker attributes associated with this method (or {@code null} if none)
*/
protected abstract CircuitBreakerAttribute findCircuitBreakerAttribute(Method method);
/**
* Subclasses need to implement this to return the circuit breaker attribute for the given class, if any.
*
* @param clazz
* the class to retrieve the attribute for
* @return all circuit breaker attributes associated with this class (or {@code null} if none)
*/
protected abstract CircuitBreakerAttribute findCircuitBreakerAttribute(Class<?> clazz);
/**
* Should only public methods be allowed to have circuit breaker wrappers?
* <p>
* The default implementation returns {@code false}.
*/
protected boolean allowPublicMethodsOnly() {
return false;
}
/**
* Default cache key for the CircuitBreakerAttribute cache.
*/
private static class DefaultCacheKey {
private final Method method;
private final Class<?> targetClass;
public DefaultCacheKey(Method method, Class<?> targetClass) {
this.method = method;
this.targetClass = targetClass;
}
@Override
public boolean equals(Object other) {
if (this == other) {
return true;
}
if (!(other instanceof DefaultCacheKey)) {
return false;
}
DefaultCacheKey otherKey = (DefaultCacheKey) other;
return (this.method.equals(otherKey.method) && ObjectUtils.nullSafeEquals(this.targetClass, otherKey.targetClass));
}
@Override
public int hashCode() {
return this.method.hashCode();
}
}
}