整体实现思路是将端点(Endpoint)适配委托给MVC层策略端点(MvcEndpoint)，再通过端点MVC适配器(EndpointMvcAdapter)将端点暴露为HTTP请求方式的MVC端点，最后分别使用端点自动配置(EndpointAutoConfiguration)和MVC方式暴露端点的配置(EndpointWebMvcManagementContextConfiguration)来注入端点组件和端点处理程序映射组件、MVC端点注册表组件、MVC端点组件。
其中，端点处理程序映射(EndpointHandlerMapping)通过Spring MVC方式来暴露MVC端点。最后，本文以“shutdown端点示例”收尾。
现在就按照整体实现思路来剖析HTTP端点的实现原理。
1、端点接口(Endpoint<T>)
/**
* An endpoint that can be used to expose useful information to operations. Usually
* exposed via Spring MVC but could also be exposed using some other technique. Consider
* extending {@link AbstractEndpoint} if you are developing your own endpoint.
* <p>一个端点可以用于暴露操作的实用信息。
*
* @param <T> the endpoint data type (端点数据类型)
* @see AbstractEndpoint
*/
// 核心接口 端点接口
public interface Endpoint<T> {
/**
* 端点的逻辑标识(字母、数字和下划线('_'))
*/
String getId();
/**
* 端点是否启用
*/
boolean isEnabled();
/**
* 端点是否输出敏感数据(安全提示)
*/
boolean isSensitive();
// 核心接口 调用端点，并返回调用结果
T invoke();
}
其抽象实现基类 AbstractEndpoint<T>
/**
* Abstract base for {@link Endpoint} implementations.
*
* @param <T> the endpoint data type (端点数据类型)
*/
// 核心类 端点实现的抽象基类
public abstract class AbstractEndpoint<T> implements Endpoint<T>, EnvironmentAware {
private Environment environment;
/**
* Endpoint identifier. With HTTP monitoring the identifier of the endpoint is mapped
* to a URL (e.g. 'foo' is mapped to '/foo').
* 端点标识符
*/
private String id;
/**
* Mark if the endpoint exposes sensitive information.
*/
private Boolean sensitive;
/**
* 是否启动端点
*/
private Boolean enabled;
public AbstractEndpoint(String id, boolean sensitive, boolean enabled) {
setId(id);
this.sensitiveDefault = sensitive;
this.enabled = enabled;
}
@Override
public void setEnvironment(Environment environment) {
this.environment = environment;
}
public void setId(String id) {
Assert.notNull(id, "Id must not be null");
Assert.isTrue(ID_PATTERN.matcher(id).matches(),
"Id must only contains letters, numbers and '_'");
this.id = id;
}
@Override
public boolean isEnabled() {
return EndpointProperties.isEnabled(this.environment, this.enabled);
}
}
2、MVC层策略端点(MvcEndpoint)
/**
* 实现类允许使用@RequestMapping和完整的Spring MVC机制，
* 但不能在类型级别使用@Controller或@RequestMapping，因为这将导致路径的双重映射，
* 一次通过常规MVC处理程序映射，一次通过{@link EndpointHandlerMapping}。
*
* @author Dave Syer
* @see NamedMvcEndpoint
*/
// 核心接口 在端点之上的MVC层策略
public interface MvcEndpoint {
/**
* 禁用端点的响应实体
*/
ResponseEntity<Map<String, String>> DISABLED_RESPONSE = new ResponseEntity<>(
Collections.singletonMap("message", "This endpoint is disabled"),
HttpStatus.NOT_FOUND);
// 核心方法 返回端点的MVC路径
String getPath();
/**
* 返回端点是否暴露敏感信息。
*/
boolean isSensitive();
// 核心方法 返回端点暴露的类型/null
@SuppressWarnings("rawtypes")
Class<? extends Endpoint> getEndpointType();
}
2.1、包括逻辑名称的MVC端点(NamedMvcEndpoint)
/**
* 名称提供了引用端点的一致方式。
*
* @author Madhura Bhave
* @since 1.5.0
*/
// 包括逻辑名称的MVC端点
public interface NamedMvcEndpoint extends MvcEndpoint {
/**
* 返回端点的逻辑名称。
*/
String getName();
}
3、端点MVC适配器(EndpointMvcAdapter)
/**
* 暴露端点({@link Endpoint})为MVC端点({@link MvcEndpoint})的适配器。
*/
// 端点MVC适配器
public class EndpointMvcAdapter extends AbstractEndpointMvcAdapter<Endpoint<?>> {
/**
* Create a new {@link EndpointMvcAdapter}.
* @param delegate the underlying {@link Endpoint} to adapt. (用于适配的底层端点)
*/
public EndpointMvcAdapter(Endpoint<?> delegate) {
super(delegate); // 委托代理
}
// 核心实现 以HTTP GET方式调用
@Override
@ActuatorGetMapping
@ResponseBody
public Object invoke() {
return super.invoke(); // 向上调用，链式模式
}
}
其抽象实现基类 AbstractEndpointMvcAdapter<E extends Endpoint<?>>
/**
* MVC端点({@link MvcEndpoint})实现的抽象基类。
*
* @param <E> The delegate endpoint (代理的端点)
* @author Dave Syer
* @since 1.3.0
*/
public abstract class AbstractEndpointMvcAdapter<E extends Endpoint<?>>
implements NamedMvcEndpoint {
/**
* 被代理的底层端点(端点子类)
*/
private final E delegate;
/**
* 端点URL路径
*/
private String path;
public AbstractEndpointMvcAdapter(E delegate) {
Assert.notNull(delegate, "Delegate must not be null");
this.delegate = delegate;
}
// 核心实现 调用底层端点，并返回调用结果
protected Object invoke() {
if (!this.delegate.isEnabled()) { // 端点被禁用
// Shouldn't happen - shouldn't be registered when delegate's disabled
return getDisabledResponse();
}
return this.delegate.invoke(); // 调用端点
}
public E getDelegate() {
return this.delegate;
}
@Override
public String getName() {
return this.delegate.getId(); // name = id
}
@Override
public String getPath() {
return (this.path != null ? this.path : "/" + this.delegate.getId()); // "/id"
}
public void setPath(String path) {
while (path.endsWith("/")) {
path = path.substring(0, path.length() - 1);
}
if (!path.startsWith("/")) {
path = "/" + path;
}
this.path = path;
}
@Override
@SuppressWarnings("rawtypes")
public Class<? extends Endpoint> getEndpointType() {
return this.delegate.getClass();
}
}
4、端点组件自动配置
基于Spring Boot的自动配置机制(Auto-configuration)，其自动配置文件位于spring-boot-actuator资源目录下的META-INF/spring.factories文件：
# 启用自动配置
org.springframework.boot.autoconfigure.EnableAutoConfiguration=\
...
org.springframework.boot.actuate.autoconfigure.EndpointAutoConfiguration,\
...
# 管理上下文配置
org.springframework.boot.actuate.autoconfigure.ManagementContextConfiguration=\
org.springframework.boot.actuate.autoconfigure.EndpointWebMvcManagementContextConfiguration,\
...
4.1、公共管理的端点自动配置(EndpointAutoConfiguration)
/**
* {@link EnableAutoConfiguration Auto-configuration} for common management
* {@link Endpoint}s.
*/
// 核心类 公共管理的端点自动配置
@Configuration // 组件配置
@AutoConfigureAfter({ FlywayAutoConfiguration.class, LiquibaseAutoConfiguration.class })
@EnableConfigurationProperties(EndpointProperties.class) // 启用配置属性(端点属性)
public class EndpointAutoConfiguration {
@Bean
@ConditionalOnMissingBean
public EnvironmentEndpoint environmentEndpoint() {
return new EnvironmentEndpoint();
}
@Bean
@ConditionalOnMissingBean
public HealthEndpoint healthEndpoint() {
return new HealthEndpoint(
this.healthAggregator == null ? new OrderedHealthAggregator()
: this.healthAggregator,
this.healthIndicators == null
? Collections.<String, HealthIndicator>emptyMap()
: this.healthIndicators);
}
@Bean
@ConditionalOnMissingBean
public TraceEndpoint traceEndpoint() {
return new TraceEndpoint(this.traceRepository == null
? new InMemoryTraceRepository() : this.traceRepository);
}
@Bean
@ConditionalOnBean(ConditionEvaluationReport.class)
@ConditionalOnMissingBean(search = SearchStrategy.CURRENT)
public AutoConfigurationReportEndpoint autoConfigurationReportEndpoint() {
return new AutoConfigurationReportEndpoint();
}
@Bean
@ConditionalOnMissingBean
public ShutdownEndpoint shutdownEndpoint() {
return new ShutdownEndpoint();
}
}
4.2、全局的端点属性(EndpointProperties)
/**
* Global endpoint properties.
* <p>全局的端点属性。
*
* @since 1.3.0
*/
@ConfigurationProperties(prefix = "endpoints") // 端点属性配置前缀
public class EndpointProperties {
private static final String ENDPOINTS_ENABLED_PROPERTY = "endpoints.enabled";
private static final String ENDPOINTS_SENSITIVE_PROPERTY = "endpoints.sensitive";
/**
* Enable endpoints.
* 启用端点
*/
private Boolean enabled = true;
/**
* Default endpoint sensitive setting.
*/
private Boolean sensitive;
public static boolean isEnabled(Environment environment, Boolean enabled) {
if (enabled != null) {
return enabled;
}
if (environment != null
&& environment.containsProperty(ENDPOINTS_ENABLED_PROPERTY)) {
return environment.getProperty(ENDPOINTS_ENABLED_PROPERTY, Boolean.class);
}
return true;
}
}
4.3、外部化配置的注解(ConfigurationProperties)
/**
* 如果要绑定和验证一些外部属性(例如来自.properties文件)，请将其添加到@Configuration类中的类定义或@Bean方法。
* <p>
* Note that contrary to {@code @Value}, SpEL expressions are not evaluated since property
* values are externalized.
*
* @author Dave Syer
* @see ConfigurationPropertiesBindingPostProcessor
* @see EnableConfigurationProperties
*/
// 外部化配置的注解
@Target({ ElementType.TYPE, ElementType.METHOD })
@Retention(RetentionPolicy.RUNTIME)
@Documented
public @interface ConfigurationProperties {
// 属性的名称前缀
@AliasFor("value")
String prefix() default "";
}
5、MVC方式暴露端点的配置(EndpointWebMvcManagementContextConfiguration)
/**
* Configuration to expose {@link Endpoint} instances over Spring MVC.
*
* @author Dave Syer
* @since 1.3.0
*/
// 核心类 通过MVC方式来暴露端点的配置
@ManagementContextConfiguration
@EnableConfigurationProperties({ HealthMvcEndpointProperties.class,
EndpointCorsProperties.class })
public class EndpointWebMvcManagementContextConfiguration {
private final HealthMvcEndpointProperties healthMvcEndpointProperties;
/**
* 管理服务器的属性
*/
private final ManagementServerProperties managementServerProperties;
private final EndpointCorsProperties corsProperties;
/**
* 端点处理程序的映射定制程序
*/
private final List<EndpointHandlerMappingCustomizer> mappingCustomizers;
// 核心方法 注入端点处理程序映射组件
@Bean
@ConditionalOnMissingBean // 组件未注入
public EndpointHandlerMapping endpointHandlerMapping() {
// 注册的MVC端点集合
Set<MvcEndpoint> endpoints = mvcEndpoints().getEndpoints();
CorsConfiguration corsConfiguration = getCorsConfiguration(this.corsProperties);
// 端点处理程序映射
EndpointHandlerMapping mapping = new EndpointHandlerMapping(endpoints,
corsConfiguration);
// 管理端点的上下文路径前缀
mapping.setPrefix(this.managementServerProperties.getContextPath());
// MVC端点安全处理程序拦截器
MvcEndpointSecurityInterceptor securityInterceptor = new MvcEndpointSecurityInterceptor(
this.managementServerProperties.getSecurity().isEnabled(),
this.managementServerProperties.getSecurity().getRoles());
mapping.setSecurityInterceptor(securityInterceptor);
for (EndpointHandlerMappingCustomizer customizer : this.mappingCustomizers) {
customizer.customize(mapping);
}
return mapping;
}
// 核心方法 注入MVC端点注册表组件
@Bean
@ConditionalOnMissingBean // 组件未注入
public MvcEndpoints mvcEndpoints() {
return new MvcEndpoints();
}
@Bean
@ConditionalOnBean(EnvironmentEndpoint.class)
@ConditionalOnEnabledEndpoint("env")
public EnvironmentMvcEndpoint environmentMvcEndpoint(EnvironmentEndpoint delegate) {
return new EnvironmentMvcEndpoint(delegate);
}
@Bean
@ConditionalOnBean(HealthEndpoint.class)
@ConditionalOnEnabledEndpoint("health")
public HealthMvcEndpoint healthMvcEndpoint(HealthEndpoint delegate) {
HealthMvcEndpoint healthMvcEndpoint = new HealthMvcEndpoint(delegate,
this.managementServerProperties.getSecurity().isEnabled());
if (this.healthMvcEndpointProperties.getMapping() != null) {
healthMvcEndpoint
.addStatusMapping(this.healthMvcEndpointProperties.getMapping());
}
return healthMvcEndpoint;
}
// 注入关闭应用程序的MVC端点组件
@Bean
@ConditionalOnBean(ShutdownEndpoint.class) // 组件已实例化
@ConditionalOnEnabledEndpoint(value = "shutdown", enabledByDefault = false) // 端点已启用
public ShutdownMvcEndpoint shutdownMvcEndpoint(ShutdownEndpoint delegate) {
return new ShutdownMvcEndpoint(delegate);
}
}
5.1、MVC端点注册表(MvcEndpoints)
/**
* 所有MVC端点组件的注册表，以及一组用于包装尚未公开的MVC端点的现有端点实例的通用工厂。
*/
// 核心类 MVC端点注册表
public class MvcEndpoints implements ApplicationContextAware, InitializingBean {
/**
* 应用上下文
*/
private ApplicationContext applicationContext;
/**
* MVC端点集合
*/
private final Set<MvcEndpoint> endpoints = new HashSet<>();
/**
* MVC端点类型集合
*/
private Set<Class<?>> customTypes;
@Override
public void setApplicationContext(ApplicationContext applicationContext)
throws BeansException {
this.applicationContext = applicationContext;
}
@Override
public void afterPropertiesSet() throws Exception {
// 现有的MVC端点列表
Collection<MvcEndpoint> existing = BeanFactoryUtils
.beansOfTypeIncludingAncestors(this.applicationContext, MvcEndpoint.class) // MVC端点
.values();
this.endpoints.addAll(existing);
this.customTypes = findEndpointClasses(existing);
// 现有的代理端点列表
@SuppressWarnings("rawtypes")
Collection<Endpoint> delegates = BeanFactoryUtils
.beansOfTypeIncludingAncestors(this.applicationContext, Endpoint.class) // 端点
.values();
for (Endpoint<?> endpoint : delegates) {
if (isGenericEndpoint(endpoint.getClass()) && endpoint.isEnabled()) {
EndpointMvcAdapter adapter = new EndpointMvcAdapter(endpoint); // 端点MVC适配器
// 端点路径
String path = determinePath(endpoint,
this.applicationContext.getEnvironment());
if (path != null) {
adapter.setPath(path);
}
this.endpoints.add(adapter);
}
}
}
private Set<Class<?>> findEndpointClasses(Collection<MvcEndpoint> existing) {
Set<Class<?>> types = new HashSet<>();
for (MvcEndpoint endpoint : existing) {
Class<?> type = endpoint.getEndpointType(); // 端点类型
if (type != null) {
types.add(type);
}
}
return types;
}
// 核心方法 返回注册的MVC端点集合
public Set<MvcEndpoint> getEndpoints() {
return this.endpoints;
}
/**
* 返回指定类型的MVC端点集合。
*/
@SuppressWarnings("unchecked")
public <E extends MvcEndpoint> Set<E> getEndpoints(Class<E> type) {
Set<E> result = new HashSet<>(this.endpoints.size());
for (MvcEndpoint candidate : this.endpoints) {
if (type.isInstance(candidate)) {
result.add((E) candidate);
}
}
return Collections.unmodifiableSet(result); // 不可修改的集合
}
// 通用的端点
private boolean isGenericEndpoint(Class<?> type) {
return !this.customTypes.contains(type)
&& !MvcEndpoint.class.isAssignableFrom(type);
}
private String determinePath(Endpoint<?> endpoint, Environment environment) {
// 配置属性
ConfigurationProperties configurationProperties = AnnotationUtils
.findAnnotation(endpoint.getClass(), ConfigurationProperties.class);
if (configurationProperties != null) {
return environment.getProperty(configurationProperties.prefix() + ".path");
}
return null;
}
}
5.2、端点处理程序映射(EndpointHandlerMapping)
/**
* @RequestMapping的语义应该与普通的@Controller相同，
* 但是端点不应该被注释为@Controller，否则它们将被正常的MVC机制映射。
* <p>
* <p>映射的目标之一是支持作为HTTP端点工作的端点，
* 但是当没有HTTP服务器(类路径上没有Spring MVC)时，仍然可以提供有用的服务接口。
* 注意：具有方法签名的任何端点将在非Servlet环境下中断。
*/
// 核心类 通过端点的逻辑标识将端点映射到URL的处理程序映射
public class EndpointHandlerMapping extends AbstractEndpointHandlerMapping<MvcEndpoint> {
/**
* Create a new {@link EndpointHandlerMapping} instance. All {@link Endpoint}s will be
* detected from the {@link ApplicationContext}. The endpoints will accepts CORS
* requests based on the given {@code corsConfiguration}.
* @param endpoints the endpoints (MVC端点列表)
* @param corsConfiguration the CORS configuration for the endpoints
* @since 1.3.0
*/
public EndpointHandlerMapping(Collection<? extends MvcEndpoint> endpoints,
CorsConfiguration corsConfiguration) {
super(endpoints, corsConfiguration);
}
}
其抽象实现基类 AbstractEndpointHandlerMapping<E extends MvcEndpoint>
/**
* @RequestMapping的语义应该与普通的@Controller相同，
* 但是端点不应该被注释为@Controller，否则它们将被正常的MVC机制映射。
* <p>映射的目标之一是支持作为HTTP端点工作的端点，
* 但是当没有HTTP服务器(类路径上没有Spring MVC)时，仍然可以提供有用的服务接口。
* 注意：具有方法签名的任何端点将在非Servlet环境下中断。
*
* @param <E> The endpoint type (端点类型)
*/
// 核心类 通过端点的逻辑标识将端点映射到URL的处理程序映射的抽象基类
public abstract class AbstractEndpointHandlerMapping<E extends MvcEndpoint>
extends RequestMappingHandlerMapping {
/**
* MVC端点集合
*/
private final Set<E> endpoints;
/**
* 安全处理程序拦截器
*/
private HandlerInterceptor securityInterceptor;
/**
* CORS配置
*/
private final CorsConfiguration corsConfiguration;
/**
* 端点的映射路径前缀
*/
private String prefix = "";
private boolean disabled = false;
/**
* Create a new {@link AbstractEndpointHandlerMapping} instance. All {@link Endpoint}s
* will be detected from the {@link ApplicationContext}. The endpoints will accepts
* CORS requests based on the given {@code corsConfiguration}.
* <p>将从应用上下文检测到所有端点。
* @param endpoints the endpoints
* @param corsConfiguration the CORS configuration for the endpoints
* @since 1.3.0
*/
public AbstractEndpointHandlerMapping(Collection<? extends E> endpoints,
CorsConfiguration corsConfiguration) {
this.endpoints = new HashSet<>(endpoints);
postProcessEndpoints(this.endpoints);
this.corsConfiguration = corsConfiguration;
// By default the static resource handler mapping is LOWEST_PRECEDENCE - 1
// and the RequestMappingHandlerMapping is 0 (we ideally want to be before both)
// 默认情况下，静态资源处理程序映射的顺序是 LOWEST_PRECEDENCE - 1
setOrder(-100);
setUseSuffixPatternMatch(false);
}
/**
* Post process the endpoint setting before they are used. Subclasses can add or
* modify the endpoints as necessary.
* <p>在使用之前，后处理端点设置。
* @param endpoints the endpoints to post process
*/
protected void postProcessEndpoints(Set<E> endpoints) {
}
@Override
public void afterPropertiesSet() {
super.afterPropertiesSet();
if (!this.disabled) { // 端点处理程序被禁用
for (MvcEndpoint endpoint : this.endpoints) {
detectHandlerMethods(endpoint);
}
}
}
// 核心实现 注册端点处理程序方法及其唯一映射
@Override
@Deprecated
protected void registerHandlerMethod(Object handler, Method method,
RequestMappingInfo mapping) {
if (mapping == null) {
return;
}
String[] patterns = getPatterns(handler, mapping);
if (!ObjectUtils.isEmpty(patterns)) {
super.registerHandlerMethod(handler, method,
withNewPatterns(mapping, patterns));
}
}
private String[] getPatterns(Object handler, RequestMappingInfo mapping) {
if (handler instanceof String) { // 组件名称
handler = getApplicationContext().getBean((String) handler);
}
Assert.state(handler instanceof MvcEndpoint, "Only MvcEndpoints are supported");
String path = getPath((MvcEndpoint) handler); // MVC端点路径
return (path == null ? null : getEndpointPatterns(path, mapping));
}
protected String getPath(MvcEndpoint endpoint) {
return endpoint.getPath();
}
// 核心实现 返回端点的路径列表
private String[] getEndpointPatterns(String path, RequestMappingInfo mapping) {
// 路径模式前缀
String patternPrefix = StringUtils.hasText(this.prefix) ? this.prefix + path
: path;
// 默认的路径集合
Set<String> defaultPatterns = mapping.getPatternsCondition().getPatterns();
if (defaultPatterns.isEmpty()) {
// 端点路径
return new String[] { patternPrefix, patternPrefix + ".json" };
}
List<String> patterns = new ArrayList<>(defaultPatterns);
for (int i = 0; i < patterns.size(); i++) {
patterns.set(i, patternPrefix + patterns.get(i)); // 端点请求路径
}
return patterns.toArray(new String[patterns.size()]);
}
// 新的端点路径
private RequestMappingInfo withNewPatterns(RequestMappingInfo mapping,
String[] patternStrings) {
// 模式请求条件
PatternsRequestCondition patterns = new PatternsRequestCondition(patternStrings,
null, null, useSuffixPatternMatch(), useTrailingSlashMatch(), null);
return new RequestMappingInfo(patterns, mapping.getMethodsCondition(),
mapping.getParamsCondition(), mapping.getHeadersCondition(),
mapping.getConsumesCondition(), mapping.getProducesCondition(),
mapping.getCustomCondition());
}
// 核心实现 获取处理程序执行链
@Override
protected HandlerExecutionChain getHandlerExecutionChain(Object handler,
HttpServletRequest request) {
HandlerExecutionChain chain = super.getHandlerExecutionChain(handler, request);
if (this.securityInterceptor == null || CorsUtils.isCorsRequest(request)) {
return chain;
}
return addSecurityInterceptor(chain);
}
private HandlerExecutionChain addSecurityInterceptor(HandlerExecutionChain chain) {
// 处理程序拦截器
List<HandlerInterceptor> interceptors = new ArrayList<>();
if (chain.getInterceptors() != null) {
interceptors.addAll(Arrays.asList(chain.getInterceptors()));
}
// 添加安全处理程序拦截器
interceptors.add(this.securityInterceptor);
return new HandlerExecutionChain(chain.getHandler(),
interceptors.toArray(new HandlerInterceptor[interceptors.size()]));
}
// 获取端点的路径
public String getPath(String endpoint) {
return this.prefix + endpoint;
}
// 返回MVC端点集合
public Set<E> getEndpoints() {
return Collections.unmodifiableSet(this.endpoints); // 不可修改的集合
}
}
5.3、组件存在条件(OnBeanCondition)
5.3.1、未注入组件条件(ConditionalOnMissingBean)
/**
* 仅当指定的组件类型或名称尚未包含在{@link BeanFactory}中时才匹配的条件。
*/
@Target({ ElementType.TYPE, ElementType.METHOD })
@Retention(RetentionPolicy.RUNTIME)
@Documented
@Conditional(OnBeanCondition.class)
public @interface ConditionalOnMissingBean {
/**
* The class type of bean that should be checked. The condition matches when each
* class specified is missing in the {@link ApplicationContext}.
* @return the class types of beans to check
*/
// 组件的类型
Class<?>[] value() default {};
String[] type() default {};
/**
* The class type of beans that should be ignored when identifying matching beans.
* @return the class types of beans to ignore
* @since 1.2.5
*/
Class<?>[] ignored() default {};
String[] ignoredType() default {};
// 装饰组件的注解类型
Class<? extends Annotation>[] annotation() default {};
// 组件的名称列表
String[] name() default {};
// 应用上下文层次结构的搜索策略
SearchStrategy search() default SearchStrategy.ALL;
}
5.3.2、组件条件(ConditionalOnBean)
/**
* 仅当指定的组件类型或名称已经包含在{@link BeanFactory}中时才匹配的条件
*/
@Target({ ElementType.TYPE, ElementType.METHOD })
@Retention(RetentionPolicy.RUNTIME)
@Documented
@Conditional(OnBeanCondition.class)
public @interface ConditionalOnBean {
/**
* The class type of bean that should be checked. The condition matches when all of
* the classes specified are contained in the {@link ApplicationContext}.
* @return the class types of beans to check
*/
// 组件的类型
Class<?>[] value() default {};
String[] type() default {};
// 装饰组件的注解类型
Class<? extends Annotation>[] annotation() default {};
// 组件的名称列表
String[] name() default {};
// 应用上下文层次结构的搜索策略
SearchStrategy search() default SearchStrategy.ALL;
}
5.3.3、启用端点条件(ConditionalOnEnabledEndpoint)
/**
* 检查端点是否启用的条件。
* 如果endpoints.<name>.enabled属性的值是true，则匹配。
*
* @since 1.2.4
*/
// 启用端点上的条件
@Retention(RetentionPolicy.RUNTIME)
@Target({ ElementType.METHOD, ElementType.TYPE })
@Documented
@Conditional(OnEnabledEndpointCondition.class)
public @interface ConditionalOnEnabledEndpoint {
// 端点的名称
String value();
/**
* Returns whether or not the endpoint is enabled by default.
*/
boolean enabledByDefault() default true;
}
6、shutdown端点示例
6.1、关闭应用程序的端点(ShutdownEndpoint)
/**
* {@link Endpoint} to shutdown the {@link ApplicationContext}.
* <p>用于优雅地关闭应用上下文({@link ApplicationContext})的端点。
* 允许应用以优雅的方式关闭
*
* @author Dave Syer
* @author Christian Dupuis
* @author Andy Wilkinson
*/
@ConfigurationProperties(prefix = "endpoints.shutdown") // 属性前缀配置
public class ShutdownEndpoint extends AbstractEndpoint<Map<String, Object>>
implements ApplicationContextAware { // 应用上下文感知
/** 无关闭上下文信息 */
private static final Map<String, Object> NO_CONTEXT_MESSAGE = Collections
.unmodifiableMap(Collections.<String, Object>singletonMap("message",
"No context to shutdown."));
/** 关闭信息 */
private static final Map<String, Object> SHUTDOWN_MESSAGE = Collections
.unmodifiableMap(Collections.<String, Object>singletonMap("message",
"Shutting down, bye..."));
/**
* 可配置的应用上下文
*/
private ConfigurableApplicationContext context;
/**
* Create a new {@link ShutdownEndpoint} instance.
*/
public ShutdownEndpoint() {
super("shutdown", true, false);
}
// 核心实现 新启线程来关闭应用上下文，并释放所有资源和锁
@Override
public Map<String, Object> invoke() {
if (this.context == null) {
return NO_CONTEXT_MESSAGE;
}
try {
return SHUTDOWN_MESSAGE;
}
finally {
Thread thread = new Thread(() -> {
try {
Thread.sleep(500L); // 使当前正在执行的线程休眠(500ms)
}
catch (InterruptedException ex) {
Thread.currentThread().interrupt(); // 如果出现中断异常，则中断当前线程
}
ShutdownEndpoint.this.context.close(); // 关闭应用上下文，并释放所有资源和锁
});
thread.setContextClassLoader(getClass().getClassLoader()); // 本类的类加载器
thread.start();
}
}
// 核心实现 设置可配置的应用上下文
@Override
public void setApplicationContext(ApplicationContext context) throws BeansException {
if (context instanceof ConfigurableApplicationContext) {
this.context = (ConfigurableApplicationContext) context;
}
}
}
6.2、关闭应用程序的MVC端点(ShutdownMvcEndpoint)
/**
* 暴露关闭应用上下文端点({@link ShutdownEndpoint})为MVC端点({@link MvcEndpoint})的适配器。
*/
// 关闭应用程序的MVC端点
@ConfigurationProperties(prefix = "endpoints.shutdown") // 属性前缀配置
public class ShutdownMvcEndpoint extends EndpointMvcAdapter {
public ShutdownMvcEndpoint(ShutdownEndpoint delegate) {
super(delegate); // 委托代理
}
// 核心实现 以HTTP POST方式调用
@PostMapping(produces = { ActuatorMediaTypes.APPLICATION_ACTUATOR_V1_JSON_VALUE,
MediaType.APPLICATION_JSON_VALUE })
@ResponseBody
@Override
public Object invoke() {
if (!getDelegate().isEnabled()) { // 端点被禁用
return getDisabledResponse();
}
return super.invoke(); // 向上调用，链式模式
}
}
至此，HTTP端点实现原理就全部分析完成。