本文源代码分析基于spring cloud 版本：Hoxton.SR3，spring cloud alibaba 版本：2.2.1.RELEASE。
1 spring cloud gateway 负载均衡入口
spring cloud gateway 使用 LoadBalancerClientFilter 来实现载均衡的功能，该过滤器通过LoadBalancerClient.choose(ServerWebExchange exchange)方法来获取目标实例。
LoadBalancerClient 为spring-cloud-commons包里提供的接口，默认实现类为netflix的RibbonLoadBalancerClient。
public class LoadBalancerClientFilter implements GlobalFilter, Ordered {
…………
//默认实现类为netflix的RibbonLoadBalancerClient
protected final LoadBalancerClient loadBalancer;
…………
public Mono<Void> filter(ServerWebExchange exchange, GatewayFilterChain chain) {
…………
final ServiceInstance instance = choose(exchange);
…………
URI requestUrl = loadBalancer.reconstructURI(
new DelegatingServiceInstance(instance, overrideScheme), uri);
…………
exchange.getAttributes().put(GATEWAY_REQUEST_URL_ATTR, requestUrl);
return chain.filter(exchange);
}
protected ServiceInstance choose(ServerWebExchange exchange) {
return loadBalancer.choose(
((URI) exchange.getAttribute(GATEWAY_REQUEST_URL_ATTR)).getHost());
}
}
2 RibbonLoadBalancerClient 大体结构
重点RibbonLoadBalancerClient的处理流程，先上一个看完源码的总结图：
加载完后对应的结构下：
3 源码简析
3.1 程序启动时创建 SpringClientFactory
Netflix所有自动配置都在spring-cloud-netflix-core-xxx.jar中，根据其META-INF/spring.factories中的配置得知，Spring Cloud Ribbon的自动配置类为 RibbonAutoConfiguration
RibbonAutoConfiguration如下：
@Configuration
@ConditionalOnClass({
IClient.class, RestTemplate.class, AsyncRestTemplate.class, Ribbon.class})
@RibbonClients
@AutoConfigureAfter(name = "org.springframework.cloud.netflix.eureka.EurekaClientAutoConfiguration")
@AutoConfigureBefore({
LoadBalancerAutoConfiguration.class, AsyncLoadBalancerAutoConfiguration.class})
@EnableConfigurationProperties(RibbonEagerLoadProperties.class)
public class RibbonAutoConfiguration {
// 所有针对某个RibbonClient指定的配置
@Autowired(required = false)
private List<RibbonClientSpecification> configurations = new ArrayList<>();
// ribbon是否懒加载的配置文件
@Autowired
private RibbonEagerLoadProperties ribbonEagerLoadProperties;
// Spring会给每个RibbonClient创建独立的ApplicationContext上下文
// 并在其上下文中创建RibbonClient对应的Bean：如IClient、ILoadbalancer等
@Bean
public SpringClientFactory springClientFactory() {
SpringClientFactory factory = new SpringClientFactory();
factory.setConfigurations(this.configurations);
return factory;
}
// Spring创建的带负载均衡功能的Client，会使用SpringClientFactory创建对应的Bean和配置
@Bean
@ConditionalOnMissingBean(LoadBalancerClient.class)
public LoadBalancerClient loadBalancerClient() {
return new RibbonLoadBalancerClient(springClientFactory());
}
// 到Spring environment中加载针对某个Client的Ribbon的核心接口实现类
@Bean
@ConditionalOnMissingBean
public PropertiesFactory propertiesFactory() {
return new PropertiesFactory();
}
// 如果不是懒加载，启动时就使用RibbonApplicationContextInitializer加载并初始化客户端配置
@Bean
@ConditionalOnProperty(value = "ribbon.eager-load.enabled", matchIfMissing = false)
public RibbonApplicationContextInitializer ribbonApplicationContextInitializer() {
return new RibbonApplicationContextInitializer(springClientFactory(),
ribbonEagerLoadProperties.getClients());
}
......
}
3.2 首次访问某个服务时创建以服务名命名的applicationContext
调用链：LoadBalancerClientFilter.choose-->RibbonLoadBalancerClient.choose-->RibbonLoadBalancerClient.getLoadBalancer-->SpringClientFactory.getLoadBalancer--> NamedContextFactory.getContext.
核心类和方法：
//## org.springframework.cloud.netflix.ribbon.SpringClientFactory
public class SpringClientFactory extends NamedContextFactory<RibbonClientSpecification> {
static final String NAMESPACE = "ribbon";
public SpringClientFactory() {
super(RibbonClientConfiguration.class, NAMESPACE, "ribbon.client.name");
}
/**
* Get the rest client associated with the name.
* @throws RuntimeException if any error occurs
*/
public <C extends IClient<?, ?>> C getClient(String name, Class<C> clientClass) {
return getInstance(name, clientClass);
}
// name代表当前Ribbon客户端，type代表要获取的实例类型，如IClient、IRule
@Override
public <C> C getInstance(String name, Class<C> type) {
// 先从父类NamedContextFactory中直接从客户端对应的ApplicationContext中获取实例
// 如果没有就根据IClientConfig中的配置找到具体的实现类，并通过反射初始化后放到Client对应的ApplicationContext中
C instance = super.getInstance(name, type);
if (instance != null) {
return instance;
}
IClientConfig config = getInstance(name, IClientConfig.class);
return instantiateWithConfig(getContext(name), type, config);
}
// 使用IClientConfig实例化
static <C> C instantiateWithConfig(AnnotationConfigApplicationContext context,
Class<C> clazz, IClientConfig config) {
C result = null;
try {
// 通过以IClientConfig为参数的构造创建clazz类实例
Constructor<C> constructor = clazz.getConstructor(IClientConfig.class);
result = constructor.newInstance(config);
} catch (Throwable e) {
// Ignored
}
// 如果没创建成功，使用无惨构造
if (result == null) {
result = BeanUtils.instantiate(clazz);
// 调用初始化配置方法
if (result instanceof IClientConfigAware) {
((IClientConfigAware) result).initWithNiwsConfig(config);
}
// 处理自动织入
if (context != null) {
context.getAutowireCapableBeanFactory().autowireBean(result);
}
}
return result;
}
}
//## 父类 org.springframework.cloud.context.named.NamedContextFactory
public abstract class NamedContextFactory<C extends NamedContextFactory.Specification>
implements DisposableBean, ApplicationContextAware {
// 维护Ribbon客户端对应的ApplicationContext上下文
private Map<String, AnnotationConfigApplicationContext> contexts = new ConcurrentHashMap<>();
// 维护Ribbon客户端的@Configuration配置类
private Map<String, C> configurations = new ConcurrentHashMap<>();
private ApplicationContext parent;
private Class<?> defaultConfigType; // 默认配置类为 RibbonClientConfiguration
private final String propertySourceName; // 默认为 ribbon
private final String propertyName; // 默认读取RibbonClient名的属性为ribbon.client.name
public NamedContextFactory(Class<?> defaultConfigType, String propertySourceName,
String propertyName) {
this.defaultConfigType = defaultConfigType;
this.propertySourceName = propertySourceName;
this.propertyName = propertyName;
}
// 如果包含Client上下文直接返回
// 如果不包含，调用createContext(name)，并放入contexts集合
protected AnnotationConfigApplicationContext getContext(String name) {
if (!this.contexts.containsKey(name)) {
synchronized (this.contexts) {
if (!this.contexts.containsKey(name)) {
this.contexts.put(name, createContext(name));
}
}
}
return this.contexts.get(name);
}
// 创建名为name的RibbonClient的ApplicationContext上下文
protected AnnotationConfigApplicationContext createContext(String name) {
AnnotationConfigApplicationContext context = new AnnotationConfigApplicationContext();
// configurations集合中是否包含当前Client相关配置类，包含即注入到ApplicationContext
if (this.configurations.containsKey(name)) {
for (Class<?> configuration : this.configurations.get(name)
.getConfiguration()) {
context.register(configuration);
}
}
//configurations集合中是否包含default.开头的通过@RibbonClients(defaultConfiguration=xxx)配置的默认配置类
for (Map.Entry<String, C> entry : this.configurations.entrySet()) {
if (entry.getKey().startsWith("default.")) {
for (Class<?> configuration : entry.getValue().getConfiguration()) {
context.register(configuration);
}
}
}
// 注册PropertyPlaceholderAutoConfiguration、RibbonClientConfiguration
context.register(PropertyPlaceholderAutoConfiguration.class,
this.defaultConfigType);
// 添加 ribbon.client.name=具体RibbonClient name的enviroment配置
context.getEnvironment().getPropertySources().addFirst(new MapPropertySource(
this.propertySourceName,
Collections.<String, Object> singletonMap(this.propertyName, name)));
// 设置父ApplicationContext，这样可以使得当前创建的子ApplicationContext可以使用父上下文中的Bean
if (this.parent != null) {
// Uses Environment from parent as well as beans
context.setParent(this.parent);
}
context.refresh(); //刷新Context
return context;
}
public <T> T getInstance(String name, Class<T> type) {
AnnotationConfigApplicationContext context = getContext(name);
if (BeanFactoryUtils.beanNamesForTypeIncludingAncestors(context,
type).length > 0) {
return context.getBean(type);
}
return null;
}
}
在context.refresh()这一行断点，内存结构如下：
3.2.1 RibbonClientConfiguration注册
上面已说明context.register(PropertyPlaceholderAutoConfiguration.class,this.defaultConfigType)
3.2.2 NacosRibbonClientConfiguration注册
由于我们引入了spring-cloud-starter-alibaba-nacos-discovery，而在RibbonNacosAutoConfiguration类中可以看到有RibbonClients注解。
@Configuration(proxyBeanMethods = false)
@EnableConfigurationProperties
@ConditionalOnBean(SpringClientFactory.class)
@ConditionalOnRibbonNacos
@ConditionalOnNacosDiscoveryEnabled
@AutoConfigureAfter(RibbonAutoConfiguration.class)
@RibbonClients(defaultConfiguration = NacosRibbonClientConfiguration.class)
public class RibbonNacosAutoConfiguration {
}
configurations配置类集合是根据@RibbonClient 和 @RibbonClients注解配置的，分别有 针对具体某个RibbonClient的配置 和 default默认配置，详见后面的 “3.2.4 RibbonClient创建"
所在在configrattions可以看到nacos针对ribbon配置
context.refresh()执行时，就会注册上面两个核心的configuration：
NacosRibbonClientConfiguration配置如下：
@Configuration(proxyBeanMethods = false)
@ConditionalOnRibbonNacos
public class NacosRibbonClientConfiguration {
@Autowired
private PropertiesFactory propertiesFactory;
@Bean
@ConditionalOnMissingBean
public ServerList<?> ribbonServerList(IClientConfig config,
NacosDiscoveryProperties nacosDiscoveryProperties) {
if (this.propertiesFactory.isSet(ServerList.class, config.getClientName())) {
ServerList serverList = this.propertiesFactory.get(ServerList.class, config,
config.getClientName());
return serverList;
}
NacosServerList serverList = new NacosServerList(nacosDiscoveryProperties);
serverList.initWithNiwsConfig(config);
return serverList;
}
@Bean
@ConditionalOnMissingBean
public NacosServerIntrospector nacosServerIntrospector() {
return new NacosServerIntrospector();
}
}
RibbonClientConfiguration配置如下：
@Import({
OkHttpRibbonConfiguration.class, RestClientRibbonConfiguration.class, HttpClientRibbonConfiguration.class})
public class RibbonClientConfiguration {
@Value("${ribbon.client.name}")
private String name = "client";
// TODO: maybe re-instate autowired load balancers: identified by name they could be
// associated with ribbon clients
@Autowired
private PropertiesFactory propertiesFactory;
@Bean
@ConditionalOnMissingBean
public IClientConfig ribbonClientConfig() {
DefaultClientConfigImpl config = new DefaultClientConfigImpl();
config.loadProperties(this.name);
return config;
}
@Bean
@ConditionalOnMissingBean
public IRule ribbonRule(IClientConfig config) {
if (this.propertiesFactory.isSet(IRule.class, name)) {
return this.propertiesFactory.get(IRule.class, config, name);
}
ZoneAvoidanceRule rule = new ZoneAvoidanceRule();
rule.initWithNiwsConfig(config);
return rule;
}
上面只截取了一段代码，给出了Ribbon相关的IClientConfig客户端配置 和 某一个核心接口IRule实现类 是如何加载配置并创建的
3.2.3 IClientConfig创建
IClientConfig就是Ribbon客户端配置的接口，可以看到先是创建了DefaultClientConfigImpl默认实现类，再config.loadProperties(this.name)加载当前Client相关的配置
//## com.netflix.client.config.DefaultClientConfigImpl#loadProperties()
/**
* Load properties for a given client. It first loads the default values for all properties,
* and any properties already defined with Archaius ConfigurationManager.
*/
@Override
public void loadProperties(String restClientName){
enableDynamicProperties = true;
setClientName(restClientName);
// 1、使用Netflix Archaius的ConfigurationManager从Spring env中加载“ribbon.配置项”这类默认配置
// 如没加载到有默认静态配置
loadDefaultValues();
// 2、使用Netflix Archaius的ConfigurationManager从Spring env中加载“client名.ribbon.配置项”这类针对某个Client的配置信息
Configuration props = ConfigurationManager.getConfigInstance().subset(restClientName);
for (Iterator<String> keys = props.getKeys(); keys.hasNext(); ){
String key = keys.next();
String prop = key;
try {
if (prop.startsWith(getNameSpace())){
prop = prop.substring(getNameSpace().length() + 1);
}
setPropertyInternal(prop, getStringValue(props, key));
} catch (Exception ex) {
throw new RuntimeException(String.format("Property %s is invalid", prop));
}
}
}
根据如上注释，如果你没有在项目中指定ribbon相关配置，那么会使用DefaultClientConfigImpl中的默认静态配置，如果Spring enviroment中包含“ribbon.配置项”这类针对所有Client的配置会被加载进来，有“client名.ribbon.配置项”这类针对某个Client的配置信息也会被加载进来
静态配置如下：
3.2.4 RibbonClient核心接口实现类配置加载及创建
上面说完IClientConfig配置项是如何加载的，按道理说其中已经包含了当前RibbonClient使用哪个核心接口实现类的配置，但Spring Cloud在此处定义了自己的实现逻辑
@Autowired
private PropertiesFactory propertiesFactory;
@Bean
@ConditionalOnMissingBean
public IRule ribbonRule(IClientConfig config) {
// 查看propertiesFactory是否有关于当前接口的配置，如有就使用，并创建实例返回
if (this.propertiesFactory.isSet(IRule.class, name)) {
return this.propertiesFactory.get(IRule.class, config, name);
}
// spring cloud 默认配置
ZoneAvoidanceRule rule = new ZoneAvoidanceRule();
rule.initWithNiwsConfig(config);
return rule;
}
下面看看PropertiesFactory的逻辑
public class PropertiesFactory {
@Autowired
private Environment environment;
private Map<Class, String> classToProperty = new HashMap<>();
public PropertiesFactory() {
classToProperty.put(ILoadBalancer.class, "NFLoadBalancerClassName");
classToProperty.put(IPing.class, "NFLoadBalancerPingClassName");
classToProperty.put(IRule.class, "NFLoadBalancerRuleClassName");
classToProperty.put(ServerList.class, "NIWSServerListClassName");
classToProperty.put(ServerListFilter.class, "NIWSServerListFilterClassName");
}
// 查看当前clazz是否在classToProperty管理的几个核心接口之一
// 如是，查看Spring environment中是否能找到 “clientName.ribbon.核心接口配置项”的配置信息
public boolean isSet(Class clazz, String name) {
return StringUtils.hasText(getClassName(clazz, name));
}
public String getClassName(Class clazz, String name) {
if (this.classToProperty.containsKey(clazz)) {
String classNameProperty = this.classToProperty.get(clazz);
String className = environment.getProperty(name + "." + NAMESPACE + "." + classNameProperty);
return className;
}
return null;
}
// 也是先调用getClassName()获取Spring enviroment中配置的核心接口实现类名
// 再使用IClientConfig配置信息创建其实例
@SuppressWarnings("unchecked")
public <C> C get(Class<C> clazz, IClientConfig config, String name) {
String className = getClassName(clazz, name);
if (StringUtils.hasText(className)) {
try {
Class<?> toInstantiate = Class.forName(className);
return (C) instantiateWithConfig(toInstantiate, config);
} catch (ClassNotFoundException e) {
throw new IllegalArgumentException("Unknown class to load "+className+" for class " + clazz + " named " + name);
}
}
return null;
}
}
故以上面创建IRule接口实现类的逻辑
● 先通过propertiesFactory查看Spring enviroment中是否配置了针对当前Ribbon Client的IRule核心接口实现类的配置信息，如有，就创建其实例返回（相关配置格式： clientName.ribbon.NFLoadBalancerRuleClassName=具体IRule实现类）
● 如没有，那么没有直接使用Netflix在其DefaultClientConfigImpl中的静态配置，而是使用Spring Cloud自定义的默认实现类，拿IRule规则接口来说是ZoneAvoidanceRule
针对每次首次访问某个client时都会执行createContext(String name)，所以首次访问时可能会慢一点。