001/**
002 * Licensed to the Apache Software Foundation (ASF) under one or more
003 * contributor license agreements.  See the NOTICE file distributed with
004 * this work for additional information regarding copyright ownership.
005 * The ASF licenses this file to You under the Apache License, Version 2.0
006 * (the "License"); you may not use this file except in compliance with
007 * the License.  You may obtain a copy of the License at
008 *
009 *      http://www.apache.org/licenses/LICENSE-2.0
010 *
011 * Unless required by applicable law or agreed to in writing, software
012 * distributed under the License is distributed on an "AS IS" BASIS,
013 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
014 * See the License for the specific language governing permissions and
015 * limitations under the License.
016 */
017package org.apache.camel.model.loadbalancer;
018
019import java.util.ArrayList;
020import java.util.List;
021import javax.xml.bind.annotation.XmlAccessType;
022import javax.xml.bind.annotation.XmlAccessorType;
023import javax.xml.bind.annotation.XmlAttribute;
024import javax.xml.bind.annotation.XmlElement;
025import javax.xml.bind.annotation.XmlRootElement;
026import javax.xml.bind.annotation.XmlTransient;
027
028import org.apache.camel.model.LoadBalancerDefinition;
029import org.apache.camel.processor.loadbalancer.CircuitBreakerLoadBalancer;
030import org.apache.camel.processor.loadbalancer.LoadBalancer;
031import org.apache.camel.spi.Metadata;
032import org.apache.camel.spi.RouteContext;
033import org.apache.camel.util.ObjectHelper;
034
035/**
036 * Circuit break load balancer
037 * <p/>
038 * The Circuit Breaker load balancer is a stateful pattern that monitors all calls for certain exceptions.
039 * Initially the Circuit Breaker is in closed state and passes all messages.
040 * If there are failures and the threshold is reached, it moves to open state and rejects all calls until halfOpenAfter
041 * timeout is reached. After this timeout is reached, if there is a new call, it will pass and if the result is
042 * success the Circuit Breaker will move to closed state, or to open state if there was an error.
043 */
044@Metadata(label = "eip,routing,loadbalance")
045@XmlRootElement(name = "circuitBreaker")
046@XmlAccessorType(XmlAccessType.FIELD)
047public class CircuitBreakerLoadBalancerDefinition extends LoadBalancerDefinition {
048    @XmlTransient
049    private List<Class<?>> exceptionTypes = new ArrayList<Class<?>>();
050    @XmlElement(name = "exception")
051    private List<String> exceptions = new ArrayList<String>();
052    @XmlAttribute
053    private Long halfOpenAfter;
054    @XmlAttribute
055    private Integer threshold;
056
057    public CircuitBreakerLoadBalancerDefinition() {
058    }
059
060    @Override
061    protected int getMaximumNumberOfOutputs() {
062        // we can only support 1 output
063        return 1;
064    }
065
066    @Override
067    protected LoadBalancer createLoadBalancer(RouteContext routeContext) {
068        CircuitBreakerLoadBalancer answer;
069
070        List<Class<?>> classes = new ArrayList<Class<?>>();
071        if (!exceptionTypes.isEmpty()) {
072            classes.addAll(exceptionTypes);
073        } else if (!exceptions.isEmpty()) {
074            for (String name : exceptions) {
075                Class<?> type = routeContext.getCamelContext().getClassResolver().resolveClass(name);
076                if (type == null) {
077                    throw new IllegalArgumentException("Cannot find class: " + name + " in the classpath");
078                }
079                if (!ObjectHelper.isAssignableFrom(Throwable.class, type)) {
080                    throw new IllegalArgumentException("Class is not an instance of Throwable: " + type);
081                }
082                classes.add(type);
083            }
084        }
085        if (classes.isEmpty()) {
086            answer = new CircuitBreakerLoadBalancer();
087        } else {
088            answer = new CircuitBreakerLoadBalancer(classes);
089        }
090
091        if (getHalfOpenAfter() != null) {
092            answer.setHalfOpenAfter(getHalfOpenAfter());
093        }
094        if (getThreshold() != null) {
095            answer.setThreshold(getThreshold());
096        }
097        return answer;
098    }
099
100    public Long getHalfOpenAfter() {
101        return halfOpenAfter;
102    }
103
104    /**
105     * The timeout in millis to use as threshold to move state from closed to half-open or open state
106     */
107    public void setHalfOpenAfter(Long halfOpenAfter) {
108        this.halfOpenAfter = halfOpenAfter;
109    }
110
111    public Integer getThreshold() {
112        return threshold;
113    }
114
115    /**
116     * Number of previous failed messages to use as threshold to move state from closed to half-open or open state
117     */
118    public void setThreshold(Integer threshold) {
119        this.threshold = threshold;
120    }
121
122    public List<String> getExceptions() {
123        return exceptions;
124    }
125
126    /**
127     * A list of class names for specific exceptions to monitor.
128     * If no exceptions is configured then all exceptions is monitored
129     */
130    public void setExceptions(List<String> exceptions) {
131        this.exceptions = exceptions;
132    }
133
134    public List<Class<?>> getExceptionTypes() {
135        return exceptionTypes;
136    }
137
138    /**
139     * A list of specific exceptions to monitor.
140     * If no exceptions is configured then all exceptions is monitored
141     */
142    public void setExceptionTypes(List<Class<?>> exceptionTypes) {
143        this.exceptionTypes = exceptionTypes;
144    }
145
146    @Override
147    public String toString() {
148        return "CircuitBreakerLoadBalancer";
149    }
150}