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CXF是一个比较流行的Web Service框架. ( 当然如果追求更高效, 还可以去搜索ice, thrift, protobuff之类的)
近一个月, 断断续续地又好好看了看CXF的一些代码, CXF的文档还是很欠缺,特别是关于内部实现的东西. 从我的感觉来说, 内部实现还是挺复杂的. Inteceptor, Feature, ConduitSelector 这些概念一大堆, 又差不多可以做类似的事情, 真是让人头晕.
CXF本身提供了一个FailoverFeature, 可以在调用服务出错时切换到其他服务器, 但是无法做到负载均衡, 我研究了几天, 在FailoverFeature的基础上改出来一个LoadBalanceFeature, 当然也同时支持Failover.
首先我们来看看如何使用CXF的FailoverFeature: (下载示例中包括使用xml和代码两种方式, 当然CXF自己还提供了使用wsdl内部定义的方式)
我们需要先准备一个HelloService, 非常简单的一个Web Service, 这里不在贴出, 具体可以看下载包
调用代码示例:
package org.javascud.extensions.cxf.testfailover;
import org.apache.cxf.clustering.FailoverFeature;
import org.apache.cxf.clustering.RandomStrategy;
import org.apache.cxf.feature.AbstractFeature;
import org.apache.cxf.jaxws.JaxWsProxyFactoryBean;
import org.javascud.extensions.cxf.service.Hello;
import java.util.ArrayList;
import java.util.List;
public class HelloServiceFailOverClient
{
public static void main(String[] args)
{
String helloFirst = "http://localhost:8080/service/Hello";
String helloSecond = "http://localhost:8081/service/Hello";
String helloThird = "http://localhost:8082/service/Hello";
String helloFour = "http://localhost:8083/service/Hello";
List<String> serviceList = new ArrayList<String>();
serviceList.add(helloFirst);
serviceList.add(helloSecond);
serviceList.add(helloThird);
//serviceList.add(helloFour);
RandomStrategy strategy = new RandomStrategy();
strategy.setAlternateAddresses(serviceList);
FailoverFeature ff = new FailoverFeature();
ff.setStrategy(strategy);
JaxWsProxyFactoryBean factory = new JaxWsProxyFactoryBean();
List<AbstractFeature> features = new ArrayList<AbstractFeature>();
features.add(ff);
factory.setFeatures(features);
factory.initFeatures();
factory.setServiceClass(Hello.class);
//factory.setAddress("http://localhost:8080/service/Hello");
Hello client = (Hello) factory.create();
String result = client.sayHello("felix");
System.out.println("result is: " + result);
}
}
在遇到错误时可以自动使用下一个服务器, 但是必须要自己设置一个地址, 如果不设置的话也可以, 但是会出错然后failover.
下面我们自己来看看我们的 LoadBalanceFeature
1. 首先我们创建一个LoadBalanceFeature (完全和FailoverFeature一样)
Feature是用来定制Server, Client, Bus的一个组件, 具体可以查看AbstractFeature, 我们使用initialize方法来定制Client, 修改Client的Conduit选择器达到负载均衡的目的.
LoadBalanceFeature代码如下:
/**
* This feature may be applied to a Client so as to enable
* load balance , use any compatible endpoint for the target service.
*
* @author Felix Zhang Date:2010-10-3 22:58
* @see org.apache.cxf.clustering.FailoverFeature
*/
public class LoadBalanceFeature extends AbstractFeature {
private LoadBalanceStrategy loadBalanceStrategy;
@Override
public void initialize(Client client, Bus bus) {
LoadBalanceTargetSelector selector = new LoadBalanceTargetSelector();
selector.setEndpoint(client.getEndpoint());
selector.setStrategy(getStrategy());
client.setConduitSelector(selector);
}
public void setStrategy(LoadBalanceStrategy strategy) {
loadBalanceStrategy = strategy;
}
public LoadBalanceStrategy getStrategy() {
return loadBalanceStrategy;
}
}
2. 定制一个LoadBalanceStrategy 负载均衡策略
负载均衡策略有很多种, 例如随机选择, 顺序选择等, FailoverFeature提供了三种策略, 总之很简单, 我们在这里就先实现随机策略, 其他的策略都很简单, 几行代码就可以实现了.
这个类主要用来设置/获取所有的提供服务的地址列表, 为了方便控制, 我新增了2个选项:
A: alwaysChangeEndpoint 是否每次请求都切换地址: 如果只有一个客户端, 可以分担负载. 缺省为true
B: removeFailedEndpoint 是否从全局的地址列表中移除失败服务地址 -- 如果你没有监测服务器状态的程序
关于动态增删服务地址
- 可以使用zookeeper等服务实时监测服务器状态, 或者自己写程序实现, 调用strategy.setAlternateAddresses即可.
- removeFailedEndpoint 如果设置为true, 但没有监测服务器状态的程序, 新增的或者复活的服务器则无法被恢复到地址列表中.
- 考虑到效率和支持failover, 设置地址列表, 移除地址等没有同步锁.
- 自动移除失败服务地址时, 目前仅支持手动地址列表, 没有考虑wsdl中的多服务地址.
- 后续我会写一个使用zookeeper增删服务地址列表的示例. (最近也在看zookeeper)
主要的代码都在AbstractLoadBalanceStrategy 中, 基本和 AbstractStaticFailoverStrategy 一样, 添加了一个removeAlternateAddress 用于移除失败的服务地址.
LoadBalanceStrategy 接口的代码如下:
/**
* Supports pluggable strategies for alternate endpoint selection on
* load balance.
* <p/>
* Random, Retries, Mod (later)
* <p/>
* 1. support load balance 2.support fail over.
*
* @author Felix Zhang Date:2010-10-1 18:14
* @see org.apache.cxf.clustering.FailoverStrategy
*/
public interface LoadBalanceStrategy {
/**
* Get the alternate endpoints for this invocation.
*
* @param exchange the current Exchange
* @return a failover endpoint if one is available
*/
List<Endpoint> getAlternateEndpoints(Exchange exchange);
/**
* Select one of the alternate endpoints for a retried invocation.
*
* @param alternates List of alternate endpoints if available
* @return the selected endpoint
*/
Endpoint selectAlternateEndpoint(List<Endpoint> alternates);
/**
* Get the alternate addresses for this invocation.
* These addresses over-ride any addresses specified in the WSDL.
*
* @param exchange the current Exchange
* @return a failover endpoint if one is available
*/
List<String> getAlternateAddresses(Exchange exchange);
/**
* Select one of the alternate addresses for a retried invocation.
*
* @param addresses List of alternate addresses if available
* @return the selected address
*/
String selectAlternateAddress(List<String> addresses);
/**
* should remove failed endpoint or not.
* only work for user defined addresses list.
* @return true or false
*/
boolean isRemoveFailedEndpoint();
/**
* change endpoint every time or not.
* @return boolean
*/
boolean isAlwaysChangeEndpoint();
/**
* remove failed address from list.
* @param address the failed address
*/
void removeAlternateAddress(String address);
}
RandomLoadBalanceStrategy继承自 AbstractLoadBalanceStrategy, 和 RandomStrategy的区别就是获取下一个服务地址时并不从列表中移除此地址, 否则就做不到负载均衡了.
3. 最重要的 LoadBalanceTargetSelector
A: 这个类比较复杂, 我们为了实现负载均衡, 修改了
prepare来动态设置调用的endpoint, 替换策略取决于LoadBalanceStrategy
主要代码如下:
boolean existsEndpoint = false;
//check current endpoint is not null
Endpoint theEndpoint = exchange.get(Endpoint.class);
if (theEndpoint.getEndpointInfo().getAddress() != null) {
existsEndpoint = true;
}
Endpoint nextEndpoint;
if (getStrategy().isAlwaysChangeEndpoint() || !existsEndpoint) {
//get a endpoint and set to current endpoint
Endpoint loadBalanceTarget = getLoadBalanceTarget(exchange);
if (loadBalanceTarget != null) {
logger.info("switch to next target: " + loadBalanceTarget.getEndpointInfo().getAddress());
setEndpoint(loadBalanceTarget);
//update exchange.org.apache.cxf.message.Message.ENDPOINT_ADDRESS --- 不设置这个就用上次的
奇怪
message.put(Message.ENDPOINT_ADDRESS, loadBalanceTarget.getEndpointInfo().getAddress());
}
nextEndpoint = loadBalanceTarget;
} else {
//use current endpoint
nextEndpoint = theEndpoint;
}
B:为了和原有Failover特性兼容, 我们修改了
getFailoverTarget函数, 在此函数中要移除失败的服务地址, 因为在之前我们修改了LoadBalanceStrategy, 它在获取地址时不再移除当前地址, 所以我们需要手动移除.
部分代码如下:
String currentAddress = getEndpoint().getEndpointInfo().getAddress();
//failover should remove current endpoint first, then get next -- 根据定义的策略来决定是否从全局地址列表中移除
if (getStrategy().isRemoveFailedEndpoint()) {
logger.warn("remove current failed address: " + currentAddress);
//remove for client, not for current invocation -- 没有同步锁
getStrategy().removeAlternateAddress(currentAddress);
}
//remove for current invocation: 当前请求中总是移除失败服务地址
alternateAddresses.remove(currentAddress);
String alternateAddress =
getStrategy().selectAlternateAddress(alternateAddresses);
4. 调用实例:
此处我们采用XML定义方式:
<?xml version="1.0" encoding="UTF-8"?>
<beans xmlns="http://www.springframework.org/schema/beans"
xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xmlns:jaxws="http://cxf.apache.org/jaxws"
xmlns:clustering="http://cxf.apache.org/clustering"
xmlns:util="http://www.springframework.org/schema/util"
xsi:schemaLocation="
http://cxf.apache.org/jaxws http://cxf.apache.org/schemas/jaxws.xsd
http://www.springframework.org/schema/beans http://www.springframework.org/schema/beans/spring-beans.xsd
http://www.springframework.org/schema/util http://www.springframework.org/schema/util/spring-util.xsd">
<util:list id="addressList">
<value>http://localhost:8081/service/Hello</value>
<value>http://localhost:8082/service/Hello</value>
<value>http://localhost:8083/service/Hello</value>
<value>http://localhost:8086/service/Hello</value>
<value>http://localhost:8087/service/Hello</value>
<value>http://localhost:8088/service/Hello</value>
</util:list>
<bean id="SequentialAddresses" class="org.apache.cxf.clustering.SequentialStrategy">
<property name="alternateAddresses">
<ref bean="addressList"/>
</property>
</bean>
<bean id="randomAddresses" class="org.javascud.extensions.cxf.RandomLoadBalanceStrategy">
<property name="alternateAddresses">
<ref bean="addressList"/>
</property>
<property name="removeFailedEndpoint" value="true" />
</bean>
<bean id="loadBalanceFeature" class="org.javascud.extensions.cxf.LoadBalanceFeature">
<property name="strategy" ref="randomAddresses" />
</bean>
<jaxws:client name="helloClient"
serviceClass="org.javascud.extensions.cxf.service.Hello" >
<jaxws:features>
<ref bean="loadBalanceFeature" />
</jaxws:features>
</jaxws:client>
</beans>
8081, 8082, 8083是实际存在的服务, 其他的不存在.
调用的Java代码:
package org.javascud.extensions.cxf.loadbalance;
import org.apache.cxf.endpoint.Client;
import org.apache.cxf.frontend.ClientProxy;
import org.javascud.extensions.cxf.LoadBalanceStrategy;
import org.javascud.extensions.cxf.service.Hello;
import org.springframework.context.support.ClassPathXmlApplicationContext;
public class HelloLoadBalanceAndFailOverClientByXML
{
public static void main(String[] args)
{
ClassPathXmlApplicationContext context
= new ClassPathXmlApplicationContext(new String[]
{"org/javascud/extensions/cxf/loadbalance/loadbalance_fail.xml"});
Hello client = (Hello) context.getBean("helloClient");
LoadBalanceStrategy strategy = (LoadBalanceStrategy) context.getBean("randomAddresses");
Client myclient = ClientProxy.getClient(client);
String address = myclient.getEndpoint().getEndpointInfo().getAddress();
System.out.println(address);
for(int i=1; i<=20; i++)
{
String result1 = client.sayHello("Felix" +i);
System.out.println("Call " + i +": " + result1);
int left = strategy.getAlternateAddresses(null).size();
System.out.println("================== left " + left + " ===========================");
}
}
}
此处仅仅为模拟测试.
5. 关于测试用例
没想好如何写单元测试, test里面目前都是随意测试的代码, 基本照顾到所有功能.
6. 下载
代码下载: http://cnscud.googlecode.com/files/extensions-cxf_20101015.zip
源码位置: http://cnscud.googlecode.com/svn/trunk/extensions/ 其中cxf目录是此文章相关的源码.
7. 有任何问题请留言.
转载请注明作者和出处 http://scud.blogjava.net