前言：
参考学习链接：
1.https://www.bilibili.com/video/BV11D4y1C73V/?spm_id_from=333.1007.top_right_bar_window_history.content.click
2.深入理解Feign之源码解析-腾讯云开发者社区-腾讯云 (tencent.com)
3.https://github.com/OpenFeign/feign
工作原理：
openFeign是一个伪客户端(以下简称Feign)，即它不做任何的请求处理。Feign通过处理注解生成request，从而实现简化HTTP API开发的目的，即开发人员可以使用注解的方式定制request api模板，在发送http request请求之前，Feign通过处理注解的方式替换掉request模板中的参数，这种实现方式显得更为直接、可理解。
问题：为何只需要定义接口而没有实现类？
拆解问题，思路分析
问题一：如何动态生成实现类？
A：动态代理（cglib 或者 jdk）
问题二：代理对象如何交给Spring容器？
A：把Bean交给Spring容器的方法有以下几种：
1.xml声明bean<bean id = "", class = "">
2.@ComponentScan @Service/@Controller/@Repository/@Component
3.Import(XXX.class)
4.ImportSelector接口，该接口返回类名数组
5.ImportBeanDefinitionRegistart接口，该接口实现registerBeanDefinitions方法
6.@Bean注解
7.FactoryBean接口，该接口实现getObject方法
8.SingletonBeanRegistry.registerSingleton()方法
其中前5种方法bean的创建交给spring负责，流程如下：
class -> beanDefinition -> bean -> cache
那么如何把一个第三方对象，也就是完全由我们自己控制创建的对象交给Spring管理呢？
6.@Bean注解
2.FactoryBean接口，该接口实现getObject方法
3.SingletonBeanRegistry.registerSingleton()方法
问题三：多个接口需要写多个对应的FactoryBean类吗？
A：不需要，原因如下：
1.只要定义一个FactoryBean类，把接口的Class作为变量传给FactoryBean
2.针对不同的接口需要创建不同的FactoryBean对象，每个FactoryBean对象所持有的接口类型是不同的
代码语言：java复制class FeignClientFactoryBean implements FactoryBean<Object> {
private Class<?> type; // 接口类型
@Override
public Object getObject() throws Exception {
// 返回代理对象
return Proxy.newProxyInstance(this.getClassLoader(),new Class<?>[] {type}, new InvocationHandler());
}
}问题四：一个FactoryBean类如何创建多个持有不同的接口类型的对象呢？
A：有两种方法
1.创建多个BeanDefinition，也就是调用BeanDefinitionBuilder.build()
2.每个BeanDefinition指定不同的接口类型
BeanDefinitionBuilder.addPropertyValue(String name, @Nullable Object value)
BeanDefinitionBuilder.addConstructorArgValue(@Nullable Object value)
问题五：如何把自定义的BeanDefinition交给Spring？
A：实现ImportBeanDefinitionRegistrar接口
需要实现registerBeanDefinitions(AnnotationMetadata importingClassMetadata, BeanDefinitionRegistry registry)
@Import、ImportSelector、ImportBeanDefinitionRegistrar的使用和区别
1）@Import(XXX.class)一般配合ImportSelector或者ImportBeanDefinitionRegistrar使用
2）ImportSelector返回的是全类名数组，用于选择需要的配置类
3）ImportBeanDefinitionRegistrar提供BeanDefinitionRegistry，用于注册自定义的BeanDefinition
问题六：如何获取带有@FeignClient注解的接口和注解信息？
A：包扫描，Spring 提供ClassPathScanningCandidateComponentProvider类做包扫描功能
代码语言：java复制public class ClassPathScanningCandidateComponentProvider implements EnvironmentCapable, ResourceLoaderAware {
private final List<TypeFilter> includeFilters = new LinkedList<>();
private final List<TypeFilter> excludeFilters = new LinkedList<>();
public Set<BeanDefinition> findCandidateComponents(String basePackage) {
if (this.componentsIndex != null && indexSupportsIncludeFilters()) {
return addCandidateComponentsFromIndex(this.componentsIndex, basePackage);
}
else {
return scanCandidateComponents(basePackage);
}
}
private Set<BeanDefinition> scanCandidateComponents(String basePackage) {
Set<BeanDefinition> candidates = new LinkedHashSet<>();
try {
String packageSearchPath = ResourcePatternResolver.CLASSPATH_ALL_URL_PREFIX
resolveBasePackage(basePackage) '/' this.resourcePattern;
Resource[] resources = getResourcePatternResolver().getResources(packageSearchPath);
for (Resource resource : resources) {
if (resource.isReadable()) {
try {
MetadataReader metadataReader = getMetadataReaderFactory().
getMetadataReader(resource);
// 第一次判断是否是候选组件
if (isCandidateComponent(metadataReader)) {
ScannedGenericBeanDefinition sbd = new ScannedGenericBeanDefinition
(metadataReader);
sbd.setResource(resource);
sbd.setSource(resource);
// 第二次判断是否是候选组件
if (isCandidateComponent(sbd)) {
candidates.add(sbd);
}
}
}
catch (Throwable ex) {
throw new BeanDefinitionStoreException(
"Failed to read candidate component class: " resource, ex);
}
}
}
}
catch (IOException ex) {
throw new BeanDefinitionStoreException("I/O failure during classpath scanning", ex);
}
return candidates;
}
/** 用类型过滤器来判断是否是候选的组件 */
protected boolean isCandidateComponent(MetadataReader metadataReader) throws IOException {
for (TypeFilter tf : this.excludeFilters) {
if (tf.match(metadataReader, getMetadataReaderFactory())) {
return false;
}
}
for (TypeFilter tf : this.includeFilters) {
if (tf.match(metadataReader, getMetadataReaderFactory())) {
return isConditionMatch(metadataReader);
}
}
return false;
}
/** 判断bean定义是否符合候选的组件:独立的并且是具体的(不是接口或抽象类) 可以重写 */
protected boolean isCandidateComponent(AnnotatedBeanDefinition beanDefinition) {
AnnotationMetadata metadata = beanDefinition.getMetadata();
return (metadata.isIndependent() && (metadata.isConcrete() ||
(metadata.isAbstract() && metadata.hasAnnotatedMethods(Lookup.class.getName()))));
}
}源码解读
@EnableFeignClients注解，关注到@Import(FeignClientsRegistrar.class)
代码语言：java复制@Import(FeignClientsRegistrar.class)
public @interface EnableFeignClients {
// basePackages的别名
String[] value() default {};
// 扫描的包
String[] basePackages() default {};
// 扫描的包的class
Class<?>[] basePackageClasses() default {};
// 默认的配置类
Class<?>[] defaultConfiguration() default {};
// 手动传入的feign client对应的Class
Class<?>[] clients() default {};
}FeignClientsRegistrar
代码语言：java复制class FeignClientsRegistrar
implements ImportBeanDefinitionRegistrar, ResourceLoaderAware, EnvironmentAware {
// 一个入口
@Override
public void registerBeanDefinitions(AnnotationMetadata metadata,
BeanDefinitionRegistry registry) {
// 注册默认配置
registerDefaultConfiguration(metadata, registry);
// 注册feign clients 关注
registerFeignClients(metadata, registry);
}
/** 注册默认配置的bean定义(FeignClientSpecification) */
private void registerDefaultConfiguration(AnnotationMetadata metadata,
BeanDefinitionRegistry registry) {
// 从EnableFeignClients注解取出所有的属性值
Map<String, Object> defaultAttrs = metadata
.getAnnotationAttributes(EnableFeignClients.class.getName(), true);
// 如果有配置defaultConfiguration
if (defaultAttrs != null && defaultAttrs.containsKey("defaultConfiguration")) {
String name;
if (metadata.hasEnclosingClass()) {
name = "default." metadata.getEnclosingClassName();
}
else {
name = "default." metadata.getClassName();
}
registerClientConfiguration(registry, name,
defaultAttrs.get("defaultConfiguration"));
}
}
/** 注册所有的feign client的bean定义(FeignClientFactoryBean) */
public void registerFeignClients(AnnotationMetadata metadata,
BeanDefinitionRegistry registry) {
// 获取扫描器
ClassPathScanningCandidateComponentProvider scanner = getScanner();
scanner.setResourceLoader(this.resourceLoader);
Set<String> basePackages;
// 获取EnableFeignClients的属性转成map对象存储
Map<String, Object> attrs = metadata
.getAnnotationAttributes(EnableFeignClients.class.getName());
// 创建注解类型的过滤器用于过滤出带有FeignClient注解的类或接口
AnnotationTypeFilter annotationTypeFilter = new AnnotationTypeFilter(
FeignClient.class);
final Class<?>[] clients = attrs == null ? null
: (Class<?>[]) attrs.get("clients");
// 现在是通过包扫描来获取接口的，也可以直接告诉它clients有哪些(但是一般不这样做)
if (clients == null || clients.length == 0) {
scanner.addIncludeFilter(annotationTypeFilter);
// 获取包
basePackages = getBasePackages(metadata);
}
else {
final Set<String> clientClasses = new HashSet<>();
basePackages = new HashSet<>();
for (Class<?> clazz : clients) {
basePackages.add(ClassUtils.getPackageName(clazz));
clientClasses.add(clazz.getCanonicalName());
}
AbstractClassTestingTypeFilter filter = new AbstractClassTestingTypeFilter() {
@Override
protected boolean match(ClassMetadata metadata) {
String cleaned = metadata.getClassName().replaceAll("\$", ".");
return clientClasses.contains(cleaned);
}
};
scanner.addIncludeFilter(
new AllTypeFilter(Arrays.asList(filter, annotationTypeFilter)));
}
/** 进行包扫描 */
for (String basePackage : basePackages) {
// 根据每一个包找出候选的bean定义
Set<BeanDefinition> candidateComponents = scanner
.findCandidateComponents(basePackage);
for (BeanDefinition candidateComponent : candidateComponents) {
if (candidateComponent instanceof AnnotatedBeanDefinition) {
AnnotatedBeanDefinition beanDefinition = (AnnotatedBeanDefinition) candidateComponent;
// 获取注解的数据
AnnotationMetadata annotationMetadata = beanDefinition.getMetadata();
// 获取FeignClient注解的属性值
Map<String, Object> attributes = annotationMetadata
.getAnnotationAttributes(
FeignClient.class.getCanonicalName());
// 获取FeignClient的名字
String name = getClientName(attributes);
// 注册每个feign client注册对应的配置(FeignClientSpecification)
registerClientConfiguration(registry, name,
attributes.get("configuration"));
// 注册feign client的bean定义(FeignClientFactoryBean)最重要的方法
registerFeignClient(registry, annotationMetadata, attributes);
}
}
}
}
/** 获取扫描器 重写第二个isCandidateComponent */
protected ClassPathScanningCandidateComponentProvider getScanner() {
return new ClassPathScanningCandidateComponentProvider(false, this.environment) {
@Override
protected boolean isCandidateComponent(
AnnotatedBeanDefinition beanDefinition) {
// 默认不是候选的组件
boolean isCandidate = false;
// 如果是独立的
if (beanDefinition.getMetadata().isIndependent()) {
// 如果不是注解
if (!beanDefinition.getMetadata().isAnnotation()) {
isCandidate = true;
}
}
return isCandidate;
}
};
}
/** 根据配置类生成并注册FeignClientSpecification的bean定义*/
private void registerClientConfiguration(BeanDefinitionRegistry registry, Object name,
Object configuration) {
BeanDefinitionBuilder builder = BeanDefinitionBuilder
.genericBeanDefinition(FeignClientSpecification.class);
builder.addConstructorArgValue(name);
builder.addConstructorArgValue(configuration);
registry.registerBeanDefinition(
name "." FeignClientSpecification.class.getSimpleName(),
builder.getBeanDefinition());
}
/** 生成并注册FeignClientFactoryBean的bean定义 */
private void registerFeignClient(BeanDefinitionRegistry registry,
AnnotationMetadata annotationMetadata, Map<String, Object> attributes) {
String className = annotationMetadata.getClassName();
// 转换成BeanDefinition FeignClientFacotryBean实现了FactoryBean接口
BeanDefinitionBuilder definition = BeanDefinitionBuilder
.genericBeanDefinition(FeignClientFactoryBean.class);
validate(attributes);
definition.addPropertyValue("url", getUrl(attributes));
definition.addPropertyValue("path", getPath(attributes));
String name = getName(attributes);
definition.addPropertyValue("name", name);
String contextId = getContextId(attributes);
definition.addPropertyValue("contextId", contextId);
definition.addPropertyValue("type", className);
definition.addPropertyValue("decode404", attributes.get("decode404"));
definition.addPropertyValue("fallback", attributes.get("fallback"));
definition.addPropertyValue("fallbackFactory", attributes.get("fallbackFactory"));
definition.setAutowireMode(AbstractBeanDefinition.AUTOWIRE_BY_TYPE);
String alias = contextId "FeignClient";
// 创建出beanDefinition
AbstractBeanDefinition beanDefinition = definition.getBeanDefinition();
boolean primary = (Boolean) attributes.get("primary"); // has a default, won't be
// null
beanDefinition.setPrimary(primary);
String qualifier = getQualifier(attributes);
if (StringUtils.hasText(qualifier)) {
alias = qualifier;
}
BeanDefinitionHolder holder = new BeanDefinitionHolder(beanDefinition, className,
new String[] { alias });
BeanDefinitionReaderUtils.registerBeanDefinition(holder, registry);
}
}FeignClientFactoryBean
代码语言：java复制class FeignClientFactoryBean
implements FactoryBean<Object>, InitializingBean, ApplicationContextAware {
private Class<?> type;
@Override
public Object getObject() throws Exception {
// 返回真正的代理对象
return getTarget();
}
/**
* @param <T> the target type of the Feign client
* @return a {@link Feign} client created with the specified data and the context
* information
*/
<T> T getTarget() {
FeignContext context = this.applicationContext.getBean(FeignContext.class);
Feign.Builder builder = feign(context);
if (!StringUtils.hasText(this.url)) {
if (!this.name.startsWith("http")) {
this.url = "http://" this.name;
}
else {
this.url = this.name;
}
this.url = cleanPath();
return (T) loadBalance(builder, context,
new HardCodedTarget<>(this.type, this.name, this.url));
}
if (StringUtils.hasText(this.url) && !this.url.startsWith("http")) {
this.url = "http://" this.url;
}
String url = this.url cleanPath();
Client client = getOptional(context, Client.class);
if (client != null) {
if (client instanceof LoadBalancerFeignClient) {
// not load balancing because we have a url,
// but ribbon is on the classpath, so unwrap
client = ((LoadBalancerFeignClient) client).getDelegate();
}
if (client instanceof FeignBlockingLoadBalancerClient) {
// not load balancing because we have a url,
// but Spring Cloud LoadBalancer is on the classpath, so unwrap
client = ((FeignBlockingLoadBalancerClient) client).getDelegate();
}
builder.client(client);
}
Targeter targeter = get(context, Targeter.class);
return (T) targeter.target(this, builder, context,
new HardCodedTarget<>(this.type, this.name, url));
}
}DefaultTargeter
代码语言：java复制class DefaultTargeter implements Targeter {
@Override
public <T> T target(FeignClientFactoryBean factory, Feign.Builder feign,
FeignContext context, Target.HardCodedTarget<T> target) {
return feign.target(target);
}
}Feign
代码语言：java复制public abstract class Feign {
public static Builder builder() {
return new Builder();
}
public <T> T target(Target<T> target) {
return build().newInstance(target);
}
public Feign build() {
SynchronousMethodHandler.Factory synchronousMethodHandlerFactory =
new SynchronousMethodHandler.Factory(client, retryer, requestInterceptors, logger,
logLevel, decode404, closeAfterDecode, propagationPolicy);
ParseHandlersByName handlersByName =
new ParseHandlersByName(contract, options, encoder, decoder, queryMapEncoder,
errorDecoder, synchronousMethodHandlerFactory);
return new ReflectiveFeign(handlersByName, invocationHandlerFactory, queryMapEncoder);
}
}ReflectiveFeign
代码语言：java复制public class ReflectiveFeign extends Feign {
private final InvocationHandlerFactory factory;
@Override
public <T> T newInstance(Target<T> target) {
Map<String, MethodHandler> nameToHandler = targetToHandlersByName.apply(target);
Map<Method, MethodHandler> methodToHandler = new LinkedHashMap<Method, MethodHandler>();
List<DefaultMethodHandler> defaultMethodHandlers = new LinkedList<DefaultMethodHandler>();
for (Method method : target.type().getMethods()) {
if (method.getDeclaringClass() == Object.class) {
continue;
} else if (Util.isDefault(method)) {
DefaultMethodHandler handler = new DefaultMethodHandler(method);
defaultMethodHandlers.add(handler);
methodToHandler.put(method, handler);
} else {
methodToHandler.put(method, nameToHandler.get(Feign.configKey(target.type(), method)));
}
}
InvocationHandler handler = factory.create(target, methodToHandler);
// jdk动态代理 主要是第三个参数
T proxy = (T) Proxy.newProxyInstance(target.type().getClassLoader(),
new Class<?>[] {target.type()}, handler);
for (DefaultMethodHandler defaultMethodHandler : defaultMethodHandlers) {
defaultMethodHandler.bindTo(proxy);
}
return proxy;
}
}总结：
只需要定义接口和注解，不需要具体的实现类
方案：根据接口动态生成代理对象，把增强功能封装在里面，然后交给Spring管理
技术点：动态代理，FactoryBean接口，包扫描，如何把自定义的Bean 定义交给spring（ImportBeanDefinitionRegistrar）, 如何把自定义的对象交给spring
如何发送http请求？
如何组件化？
定义接口，该接口用来发送请求和响应请求
代码语言：java复制public interface Client {
Response execute(Request request, Options options) throws IOException;
}已有方案有哪些？
1.rest template
2.http client
3.okhttp
如何整合已有的方案？
利用适配器模式
HttpClientAdapter里的代理对象是已有方案HttpClient，在真正调用Client的excute方法的时候，实际调用的是HttpClient的excute
代码语言：java复制/** http client的适配器 */
public final class ApacheHttpClient implements Client {
private final HttpClient client;
public ApacheHttpClient(HttpClient client) {
this.client = client;
}
@Override
public Response execute(Request request, Request.Options options) throws IOException {
HttpUriRequest httpUriRequest;
try {
// 在这里进行了转换openfeign的->http的
httpUriRequest = toHttpUriRequest(request, options);
} catch (URISyntaxException e) {
throw new IOException("URL '" request.url() "' couldn't be parsed into a URI", e);
}
// http的->openfeign
HttpResponse httpResponse = client.execute(httpUriRequest);
return toFeignResponse(httpResponse, request);
}
}
/** ok http 的适配器 */
public final class OkHttpClient implements Client {
private final okhttp3.OkHttpClient delegate;
public OkHttpClient(okhttp3.OkHttpClient delegate) {
this.delegate = delegate;
}
@Override
public feign.Response execute(feign.Request input, feign.Request.Options options)
throws IOException {
okhttp3.OkHttpClient requestScoped;
if (delegate.connectTimeoutMillis() != options.connectTimeoutMillis()
|| delegate.readTimeoutMillis() != options.readTimeoutMillis()) {
requestScoped = delegate.newBuilder()
.connectTimeout(options.connectTimeoutMillis(), TimeUnit.MILLISECONDS)
.readTimeout(options.readTimeoutMillis(), TimeUnit.MILLISECONDS)
.followRedirects(options.isFollowRedirects())
.build();
} else {
requestScoped = delegate;
}
Request request = toOkHttpRequest(input);
Response response = requestScoped.newCall(request).execute();
return toFeignResponse(response, input).toBuilder().request(input).build();
}
}注意需要引入以下依赖
代码语言：html复制<dependency>
<groupId>io.github.openfeign</groupId>
<artifactId>feign-httpclient</artifactId>
</dependency>
<dependency>
<groupId>io.github.openfeign</groupId>
<artifactId>feign-okhttp</artifactId>
</dependency>如何动态选择实现方案？
插拔式
1.Java SPI -> 无法提供依赖注入，无法动态选择实现类
2.Dubbo SPI -> 额外添加Dubbo依赖，Dubbo SPI与业务模型耦合
3.SpringBoot的自动装配 -> OpenFeign作为SpringCloud组件之一直接依托于SpringBoot
tips:找自动装配类的技巧：
1.Ctrl G -> find Usages 功能 寻找new Instance
2.通过名字去猜 autoconfiguration结尾， 其中带有feign开头
3.直接通过 spring.factories 文件去搜索
feign带负载均衡的自动装配类
代码语言：java复制// 按照import的顺序 httpclient -> okhttp -> jdk
@Import({ HttpClientFeignLoadBalancedConfiguration.class,
OkHttpFeignLoadBalancedConfiguration.class,
DefaultFeignLoadBalancedConfiguration.class })
public class FeignRibbonClientAutoConfiguration {
// ...
}HttpClient适配器的配置类
代码语言：java复制@Configuration(proxyBeanMethods = false)
@ConditionalOnClass(ApacheHttpClient.class)
@ConditionalOnProperty(value = "feign.httpclient.enabled", matchIfMissing = true)
@Import(HttpClientFeignConfiguration.class)
class HttpClientFeignLoadBalancedConfiguration {
@Bean
@ConditionalOnMissingBean(Client.class)
public Client feignClient(CachingSpringLoadBalancerFactory cachingFactory,
SpringClientFactory clientFactory, HttpClient httpClient) {
ApacheHttpClient delegate = new ApacheHttpClient(httpClient);
return new LoadBalancerFeignClient(delegate, cachingFactory, clientFactory);
}
}HttpClient的配置类
代码语言：java复制@Configuration(proxyBeanMethods = false)
@ConditionalOnMissingBean(CloseableHttpClient.class)
public class HttpClientFeignConfiguration {
private final Timer connectionManagerTimer = new Timer(
"FeignApacheHttpClientConfiguration.connectionManagerTimer", true);
private CloseableHttpClient httpClient;
@Autowired(required = false)
private RegistryBuilder registryBuilder;
@Bean
@ConditionalOnMissingBean(HttpClientConnectionManager.class)
public HttpClientConnectionManager connectionManager(
ApacheHttpClientConnectionManagerFactory connectionManagerFactory,
FeignHttpClientProperties httpClientProperties) {
final HttpClientConnectionManager connectionManager = connectionManagerFactory
.newConnectionManager(httpClientProperties.isDisableSslValidation(),
httpClientProperties.getMaxConnections(),
httpClientProperties.getMaxConnectionsPerRoute(),
httpClientProperties.getTimeToLive(),
httpClientProperties.getTimeToLiveUnit(), this.registryBuilder);
this.connectionManagerTimer.schedule(new TimerTask() {
@Override
public void run() {
connectionManager.closeExpiredConnections();
}
}, 30000, httpClientProperties.getConnectionTimerRepeat());
return connectionManager;
}
// ...
@Bean
@ConditionalOnProperty(value = "feign.compression.response.enabled",
havingValue = "false", matchIfMissing = true)
public CloseableHttpClient httpClient(ApacheHttpClientFactory httpClientFactory,
HttpClientConnectionManager httpClientConnectionManager,
FeignHttpClientProperties httpClientProperties) {
this.httpClient = createClient(httpClientFactory.createBuilder(),
httpClientConnectionManager, httpClientProperties);
return this.httpClient;
}
private CloseableHttpClient createClient(HttpClientBuilder builder,
HttpClientConnectionManager httpClientConnectionManager,
FeignHttpClientProperties httpClientProperties) {
RequestConfig defaultRequestConfig = RequestConfig.custom()
.setConnectTimeout(httpClientProperties.getConnectionTimeout())
.setRedirectsEnabled(httpClientProperties.isFollowRedirects()).build();
CloseableHttpClient httpClient = builder
.setDefaultRequestConfig(defaultRequestConfig)
.setConnectionManager(httpClientConnectionManager).build();
return httpClient;
}
}如何装配组件？
A：SynchronousMethodHandler
代码语言：java复制public class ReflectiveFeign extends Feign {
// ...
/** 创建JDK动态代理对象 */
@Override
public <T> T newInstance(Target<T> target) {
Map<String, MethodHandler> nameToHandler = targetToHandlersByName.apply(target);
Map<Method, MethodHandler> methodToHandler = new LinkedHashMap<Method, MethodHandler>();
List<DefaultMethodHandler> defaultMethodHandlers = new LinkedList<DefaultMethodHandler>();
for (Method method : target.type().getMethods()) {
if (method.getDeclaringClass() == Object.class) {
continue;
} else if (Util.isDefault(method)) {
DefaultMethodHandler handler = new DefaultMethodHandler(method);
defaultMethodHandlers.add(handler);
methodToHandler.put(method, handler);
} else {
methodToHandler.put(method, nameToHandler.get(Feign.configKey(target.type(), method)));
}
}
// 通过工厂创建FeignInvocationHandler对象并把methodToHandler封装进去
InvocationHandler handler = factory.create(target, methodToHandler);
// JDK动态代理的API
T proxy = (T) Proxy.newProxyInstance(target.type().getClassLoader(),
new Class<?>[] {target.type()}, handler);
for (DefaultMethodHandler defaultMethodHandler : defaultMethodHandlers) {
defaultMethodHandler.bindTo(proxy);
}
return proxy;
}
// jdk动态代理的第三个参数InvocationHandler
static class FeignInvocationHandler implements InvocationHandler {
private final Target target;
private final Map<Method, MethodHandler> dispatch; // 每个方法封装到MethodHandler
FeignInvocationHandler(Target target, Map<Method, MethodHandler> dispatch) {
this.target = checkNotNull(target, "target");
this.dispatch = checkNotNull(dispatch, "dispatch for %s", target);
}
@Override
public Object invoke(Object proxy, Method method, Object[] args) throws Throwable {
if ("equals".equals(method.getName())) {
try {
Object otherHandler =
args.length > 0 && args[0] != null ? Proxy.getInvocationHandler(args[0]) : null;
return equals(otherHandler);
} catch (IllegalArgumentException e) {
return false;
}
} else if ("hashCode".equals(method.getName())) {
return hashCode();
} else if ("toString".equals(method.getName())) {
return toString();
}
return dispatch.get(method).invoke(args);
}
}
}final class SynchronousMethodHandler implements MethodHandler {
private final MethodMetadata metadata;
private final Target<?> target;
private final Client client; // http 请求客户端
private final Retryer retryer;
private final List<RequestInterceptor> requestInterceptors;
private final Logger logger;
private final Logger.Level logLevel;
private final RequestTemplate.Factory buildTemplateFromArgs;
private final Options options;
// ...
private SynchronousMethodHandler(Target<?> target, Client client, Retryer retryer,
List<RequestInterceptor> requestInterceptors, Logger logger,
Logger.Level logLevel, MethodMetadata metadata,
RequestTemplate.Factory buildTemplateFromArgs, Options options,
Decoder decoder, ErrorDecoder errorDecoder, boolean decode404,
boolean closeAfterDecode, ExceptionPropagationPolicy propagationPolicy) {
// ...
this.client = checkNotNull(client, "client for %s", target);
// ...
}
/** 真正地调用每个方法 */
@Override
public Object invoke(Object[] argv) throws Throwable {
RequestTemplate template = buildTemplateFromArgs.create(argv);
Options options = findOptions(argv);
Retryer retryer = this.retryer.clone();
while (true) {
try {
// 调用client
return executeAndDecode(template, options);
} catch (RetryableException e) {
try {
retryer.continueOrPropagate(e);
} catch (RetryableException th) {
Throwable cause = th.getCause();
if (propagationPolicy == UNWRAP && cause != null) {
throw cause;
} else {
throw th;
}
}
if (logLevel != Logger.Level.NONE) {
logger.logRetry(metadata.configKey(), logLevel);
}
continue;
}
}
}
/** 该方法是通RequestTemplate生成Request请求对象 然后根据用client获取response*/
Object executeAndDecode(RequestTemplate template, Options options) throws Throwable {
// 请求对象
Request request = targetRequest(template);
if (logLevel != Logger.Level.NONE) {
logger.logRequest(metadata.configKey(), logLevel, request);
}
Response response;
long start = System.nanoTime();
try {
// 响应对象 调用client组件的execute方法
response = client.execute(request, options);
} catch (IOException e) {
if (logLevel != Logger.Level.NONE) {
logger.logIOException(metadata.configKey(), logLevel, e, elapsedTime(start));
}
throw errorExecuting(request, e);
}
// ...
}
}如何获取组件？
1.Autowired自动装配
2.获取BeanFactory或ApplicatonContext
顶级Parent Application context -> FeignContext -> FeignContext -> Map<> contexts -> 包含了子模块Service Application context
如何传递组件？
Feign.builder() 传给 SynchronousMethodHandler.Factory -> SynchronousMethodHandler
总结：
设计：组件化思维
技术点：适配器模式，SpringBoot自动装配，父子容器
OpenFeign的源码实现过程如下：
- 通过@EnableFeignClients注解开启FeignClient
- 根据Feign的规则实现接口，加上FeignClient注解
- Application程序启动进行包扫描，扫描所有@FeignClient注解的类，把这些信息注入ioc容器
- 当接口的方法被调用通过jdk动态代理，生成具体的RequesTemplate
- RequesTemplate再生成Request对象
- Request对象交给Client组件处理
- Client组件封装到LoadBalanceClient类，该类结合Ribbon实现负载均衡
以上内容仅为个人学习所用，如有侵权请联系！
