camel-core/src/main/java/org/apache/camel/model/LoadBalanceDefinition.java

/**
 * Licensed to the Apache Software Foundation (ASF) under one or more
 * contributor license agreements.  See the NOTICE file distributed with
 * this work for additional information regarding copyright ownership.
 * The ASF licenses this file to You 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 org.apache.camel.model;

import java.util.ArrayList;
import java.util.Arrays;
import java.util.Collection;
import java.util.List;
import javax.xml.bind.annotation.XmlAccessType;
import javax.xml.bind.annotation.XmlAccessorType;
import javax.xml.bind.annotation.XmlAttribute;
import javax.xml.bind.annotation.XmlElement;
import javax.xml.bind.annotation.XmlElementRef;
import javax.xml.bind.annotation.XmlElements;
import javax.xml.bind.annotation.XmlRootElement;

import org.apache.camel.Expression;
import org.apache.camel.Processor;
import org.apache.camel.model.loadbalancer.FailoverLoadBalancerDefinition;
import org.apache.camel.model.loadbalancer.RandomLoadBalancerDefinition;
import org.apache.camel.model.loadbalancer.RoundRobinLoadBalancerDefinition;
import org.apache.camel.model.loadbalancer.StickyLoadBalancerDefinition;
import org.apache.camel.model.loadbalancer.TopicLoadBalancerDefinition;
import org.apache.camel.processor.SendProcessor;
import org.apache.camel.processor.loadbalancer.FailOverLoadBalancer;
import org.apache.camel.processor.loadbalancer.LoadBalancer;
import org.apache.camel.processor.loadbalancer.RandomLoadBalancer;
import org.apache.camel.processor.loadbalancer.RoundRobinLoadBalancer;
import org.apache.camel.processor.loadbalancer.StickyLoadBalancer;
import org.apache.camel.processor.loadbalancer.TopicLoadBalancer;
import org.apache.camel.spi.RouteContext;
import org.apache.camel.util.CollectionStringBuffer;

/**
 * Represents an XML <loadBalance/> element
 */
@XmlRootElement(name = "loadBalance")
@XmlAccessorType(XmlAccessType.FIELD)
public class LoadBalanceDefinition extends ProcessorDefinition<LoadBalanceDefinition> {
    @XmlAttribute(required = false)
    private String ref;

    @XmlElements({
            @XmlElement(required = false, name = "failover", type = FailoverLoadBalancerDefinition.class),
            @XmlElement(required = false, name = "random", type = RandomLoadBalancerDefinition.class),
            @XmlElement(required = false, name = "roundRobin", type = RoundRobinLoadBalancerDefinition.class),
            @XmlElement(required = false, name = "sticky", type = StickyLoadBalancerDefinition.class),
            @XmlElement(required = false, name = "topic", type = TopicLoadBalancerDefinition.class)}
    )
    private LoadBalancerDefinition loadBalancerType;

    @XmlElementRef
    private List<ProcessorDefinition> outputs = new ArrayList<ProcessorDefinition>();

    public LoadBalanceDefinition() {
    }

    @Override
    public String getShortName() {
        return "loadbalance";
    }

    public List<ProcessorDefinition> getOutputs() {
        return outputs;
    }

    public void setOutputs(List<ProcessorDefinition> outputs) {
        this.outputs = outputs;
        if (outputs != null) {
            for (ProcessorDefinition<?> output : outputs) {
                configureChild(output);
            }
        }
    }

    public String getRef() {
        return ref;
    }

    public void setRef(String ref) {
        this.ref = ref;
    }

    public LoadBalancerDefinition getLoadBalancerType() {
        return loadBalancerType;
    }

    public void setLoadBalancerType(LoadBalancerDefinition loadbalancer) {
        loadBalancerType = loadbalancer;
    }

    protected Processor createOutputsProcessor(RouteContext routeContext,
                                               Collection<ProcessorDefinition> outputs) throws Exception {
        LoadBalancer loadBalancer = LoadBalancerDefinition.getLoadBalancer(routeContext, loadBalancerType, ref);
        for (ProcessorDefinition<?> processorType : outputs) {
            // The outputs should be the SendProcessor
            SendProcessor processor = (SendProcessor) processorType.createProcessor(routeContext);
            loadBalancer.addProcessor(processor);
        }
        return loadBalancer;
    }
    
    @Override
    public Processor createProcessor(RouteContext routeContext) throws Exception {
        LoadBalancer loadBalancer = LoadBalancerDefinition.getLoadBalancer(routeContext, loadBalancerType, ref);
        for (ProcessorDefinition<?> processorType : getOutputs()) {            
            Processor processor = processorType.createProcessor(routeContext);
            processor = wrapProcessor(routeContext, processor);
            loadBalancer.addProcessor(processor);
        }
        return loadBalancer;
    }
    
    // Fluent API
    // -------------------------------------------------------------------------

    /**
     * Uses a custom load balancer
     *
     * @param loadBalancer  the load balancer
     * @return the builder
     */
    public LoadBalanceDefinition loadBalance(LoadBalancer loadBalancer) {
        loadBalancerType = new LoadBalancerDefinition(loadBalancer);
        return this;
    }
    
    /**
     * Uses fail over load balancer
     * <p/>
     * Will not round robin and inherit the error handler.
     *
     * @return the builder
     */
    public LoadBalanceDefinition failover() {
        return failover(-1, true, false);
    }
    
    /**
     * Uses fail over load balancer
     * <p/>
     * Will not round robin and inherit the error handler.
     *
     * @param exceptions exception classes which we want to failover if one of them was thrown
     * @return the builder
     */
    public LoadBalanceDefinition failover(Class<?>... exceptions) {
        return failover(-1, true, false, exceptions);
    }

    /**
     * Uses fail over load balancer
     *
     * @param maximumFailoverAttempts  maximum number of failover attempts before exhausting.
     *                                 Use -1 to newer exhaust when round robin is also enabled.
     *                                 If round robin is disabled then it will exhaust when there are no more endpoints to failover
     * @param inheritErrorHandler      whether or not to inherit error handler.
     *                                 If <tt>false</tt> then it will failover immediately in case of an exception
     * @param roundRobin               whether or not to use round robin (which keeps state)
     * @param exceptions               exception classes which we want to failover if one of them was thrown
     * @return the builder
     */
    public LoadBalanceDefinition failover(int maximumFailoverAttempts, boolean inheritErrorHandler, boolean roundRobin, Class<?>... exceptions) {
        FailOverLoadBalancer failover = new FailOverLoadBalancer(Arrays.asList(exceptions));
        failover.setMaximumFailoverAttempts(maximumFailoverAttempts);
        failover.setRoundRobin(roundRobin);
        loadBalancerType = new LoadBalancerDefinition(failover);
        this.setInheritErrorHandler(inheritErrorHandler);
        return this;
    }

    /**
     * Uses round robin load balancer
     *
     * @return the builder
     */
    public LoadBalanceDefinition roundRobin() {
        loadBalancerType = new LoadBalancerDefinition(new RoundRobinLoadBalancer());
        return this;
    }

    /**
     * Uses random load balancer
     * @return the builder
     */
    public LoadBalanceDefinition random() {
        loadBalancerType = new LoadBalancerDefinition(new RandomLoadBalancer());
        return this;
    }

    /**
     * Uses sticky load balancer
     *
     * @param correlationExpression  the expression for correlation
     * @return  the builder
     */
    public LoadBalanceDefinition sticky(Expression correlationExpression) {
        loadBalancerType = new LoadBalancerDefinition(new StickyLoadBalancer(correlationExpression));
        return this;
    }

    /**
     * Uses topic load balancer
     * 
     * @return the builder
     */
    public LoadBalanceDefinition topic() {
        loadBalancerType = new LoadBalancerDefinition(new TopicLoadBalancer());
        return this;
    }

    @Override
    public String getLabel() {
        CollectionStringBuffer buffer = new CollectionStringBuffer();
        List<ProcessorDefinition> list = getOutputs();
        for (ProcessorDefinition processorType : list) {
            buffer.append(processorType.getLabel());
        }
        return buffer.toString();
    }

    @Override
    public String toString() {
        if (loadBalancerType != null) {
            return "LoadBalanceType[" + loadBalancerType + ", " + getOutputs() + "]";
        } else {
            return "LoadBalanceType[ref:" + ref + ", " + getOutputs() + "]";
        }
    }
}