前言

之前的几篇文章分析了spring boot 中有关endpoint的实现,细心的朋友可以发现,在org.springframework.boot.actuate.endpoint.mvc 包下也有一系列的xxxEndpoint,这又是为什么呢?

原因是: 我们很多情况下,都是访问接口的方式获取应用的监控,之前的分析是其实现的底层,要想实现通过接口访问,还需要对其进行包装一番,org.springframework.boot.actuate.endpoint.mvc 包下的实现就是干的这种事,下面,我们就来分析一下吧

解析

关于mvcEndPoint的类图如下,

mvc-endpoint-class-uml

下面我们就来1个1个的来分析吧.

MvcEndpoint

MvcEndpoint –> 顶层接口,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EndpointHandlerMapping。

该类声明如下:

public interface MvcEndpoint {// 禁用端点的响应实体
ResponseEntity<Map<String, String>> DISABLED_RESPONSE = new ResponseEntity<Map<String, String>>(Collections.singletonMap("message", "This endpoint is disabled"),HttpStatus.NOT_FOUND);// 返回端点的MVC路径
String getPath();// 返回端点是否暴露敏感信息
boolean isSensitive();// 返回端点暴露的类型。或者返回null 如果当前的MvcEndpoint 暴露的信息 不能视为一个传统的Endpoint(也就是我们之前分析的那一堆Endpoint)
Class<? extends Endpoint> getEndpointType();
}

AbstractMvcEndpoint

AbstractMvcEndpoint继承了WebMvcConfigurerAdapter,实现了MvcEndpoint, EnvironmentAware接口,此时 AbstractMvcEndpoint 就持有了Environment,可以对spring mvc 做个性化设置.

字段,构造器分别如下:

// Endpoint 请求路径
private String path;// endpoint是否可用
private Boolean enabled;// 标识该endpoint 是否暴露了敏感数据,如果为true,访问该Endpoint需要进行校验
private Boolean sensitive;// 是否默认敏感
private final boolean sensitiveDefault;public AbstractMvcEndpoint(String path, boolean sensitive) {setPath(path);this.sensitiveDefault = sensitive;
}public AbstractMvcEndpoint(String path, boolean sensitive, boolean enabled) {setPath(path);this.sensitiveDefault = sensitive;this.enabled = enabled;
}

AbstractMvcEndpoint 实现了MvcEndpoint的方法,分别如下:

getPath,直接返回其字段值即可,代码如下:
```
public String getPath() {
return this.path;
}
```

isSensitive–> 默认返回false.代码如下:

public boolean isSensitive() {
// 默认返回false
return EndpointProperties.isSensitive(this.environment, this.sensitive,this.sensitiveDefault);
}

调用:

public static boolean isSensitive(Environment environment, Boolean sensitive,boolean sensitiveDefault) {
// 1. 如果sensitive 不等于null,则直接返回
if (sensitive != null) {return sensitive;
}
// 2. 如果environment 不等于null 并且 environment中配置有endpoints.sensitive的属性,则
// 返回其配置值
if (environment != null&& environment.containsProperty(ENDPOINTS_SENSITIVE_PROPERTY)) {return environment.getProperty(ENDPOINTS_SENSITIVE_PROPERTY, Boolean.class);
}
// 3. 返回给的默认值
return sensitiveDefault;
}

如果sensitive 不等于null,则直接返回
如果environment 不等于null 并且 environment中配置有endpoints.sensitive的属性,则返回其配置值
返回给的默认值

getEndpointType –> 默认返回null,代码如下:

public Class<? extends Endpoint> getEndpointType() {
return null;
}

此外,该类还声明了1个方法,判断当前端点是否可用,默认返回true代码如下:

public boolean isEnabled() {// 默认返回truereturn EndpointProperties.isEnabled(this.environment, this.enabled);
}

调用:

public static boolean isEnabled(Environment environment, Boolean enabled) {// 1. 如果enabled 不为null,则进行返回.if (enabled != null) {return enabled;}// 2. 如果Environment 不等于null 并且Environment 配置有endpoints.enabled的属性,// 则返回其配置的值if (environment != null&& environment.containsProperty(ENDPOINTS_ENABLED_PROPERTY)) {return environment.getProperty(ENDPOINTS_ENABLED_PROPERTY, Boolean.class);}// 3. 默认为truereturn true;
}

如果enabled 不为null,则进行返回.
如果Environment 不等于null 并且Environment 配置有endpoints.enabled的属性,则返回其配置的值
默认为true

NamedMvcEndpoint

NamedMvcEndpoint继承自MvcEndpoint,使一个MvcEndpoint可以包含一个逻辑名.不像getPath()–>它没有给用户一个机会去改变endpoint的名字.NamedMvcEndpoint 提供了一个一致的方式去引用一个endpoint.

该类声明了1个方法,如下:

// 返回一个逻辑名字,不能为null,空,字母数字组成
String getName();

AbstractNamedMvcEndpoint

该类继承自AbstractMvcEndpoint,实现了NamedMvcEndpoint接口.

字段,构造器如下:

// Endpoint 名字
private final String name;public AbstractNamedMvcEndpoint(String name, String path, boolean sensitive) {super(path, sensitive);Assert.hasLength(name, "Name must not be empty");this.name = name;
}public AbstractNamedMvcEndpoint(String name, String path, boolean sensitive,boolean enabled) {super(path, sensitive, enabled);Assert.hasLength(name, "Name must not be empty");this.name = name;
}

getName,只需返回name属性值即可,很简单,代码如下:
```
public String getName() {return this.name;
}
```

该类的子类有:

AuditEventsMvcEndpoint
DocsMvcEndpoint
HalJsonMvcEndpoint
HeapdumpMvcEndpoint
JolokiaMvcEndpoint
LogFileMvcEndpoint

这些子类的实现我们后续进行分析…

AbstractEndpointMvcAdapter

AbstractEndpointMvcAdapter 实现了NamedMvcEndpoint接口,是MvcEndpoint的抽象基类

字段,构造器如下:

// 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;
}

NamedMvcEndpoint接口方法实现如下:

getName,返回被代理的Endpoint的id,代码如下:

public String getName() {
return this.delegate.getId();
}

getPath –> 如果path不等于null,则直接返回,否则使用/+Endpoint的id,代码如下:

public String getPath() {
// 如果path不等于null,则直接返回,否则使用/+Endpoint的id
return (this.path != null ? this.path : "/" + this.delegate.getId());
}

isSensitive–> 直接调用被代理的Endpoint的isSensitive方法即可.代码如下:
```
public boolean isSensitive() {
return this.delegate.isSensitive();
}
```

getEndpointType –> 返回被代理的 Endpoint的类型即可,代码如下:

public Class<? extends Endpoint> getEndpointType() {
return this.delegate.getClass();
}

AbstractEndpointMvcAdapter 还声明了2个方法,供子类使用

getDisabledResponse–> 返回该相应当所代理的endpoint不可用时.代码如下:

protected ResponseEntity<?> getDisabledResponse() {
return MvcEndpoint.DISABLED_RESPONSE;
}

即:

ResponseEntity<Map<String, String>> DISABLED_RESPONSE = new ResponseEntity<Map<String, String>>(Collections.singletonMap("message", "This endpoint is disabled"),HttpStatus.NOT_FOUND);

invoke–> 调用代理的Endpoint，并返回调用结果,代码如下:
```
protected Object invoke() {
if (!this.delegate.isEnabled()) {return getDisabledResponse();
}
return this.delegate.invoke();
}
```
1. 端点不可用(禁用),则返回默认的不可用信息.当Endpoint被禁用时,是不会注册的.
2. 否则,调用Endpoint的invoke方法

EndpointMvcAdapter

EndpointMvcAdapter,继承自AbstractEndpointMvcAdapter,将Endpoint适配为MvcEndpoint. 构造器如下:
```
public EndpointMvcAdapter(Endpoint<?> delegate) {super(delegate);
}
```

该类覆写了invoke,使其能过被spring mvc 处理–> 暴露接口(关于这部分,我们后续有分析),代码如下:

@Override
@ActuatorGetMapping
@ResponseBody
public Object invoke() {return super.invoke();
}

其中@ActuatorGetMapping 就是@RequestMapping的封装,被该注解标注的方法,其请求方式为get,产生的数据格式为application/vnd.spring-boot.actuator.v1+json和application/json.代码如下:

@Target(ElementType.METHOD)
@Retention(RetentionPolicy.RUNTIME)
@Documented
@RequestMapping(method = RequestMethod.GET, produces = {ActuatorMediaTypes.APPLICATION_ACTUATOR_V1_JSON_VALUE,MediaType.APPLICATION_JSON_VALUE })
@interface ActuatorGetMapping {/*** Alias for {@link RequestMapping#value}.* @return the value*/
@AliasFor(annotation = RequestMapping.class)
String[] value() default {};
}

EnvironmentMvcEndpoint

该类继承自EndpointMvcAdapter,实现了EnvironmentAware,因此,该类也就持有了Environment.

字段,构造器如下:

private Environment environment;public EnvironmentMvcEndpoint(EnvironmentEndpoint delegate) {super(delegate);
}

此时, EnvironmentMvcEndpoint 也就持有了EnvironmentEndpoint的实例

该类声明了1个被@ActuatorGetMapping注解的方法,value,代码如下:

@ActuatorGetMapping("/{name:.*}")
@ResponseBody
@HypermediaDisabled
public Object value(@PathVariable String name) {if (!getDelegate().isEnabled()) {// Shouldn't happen - MVC endpoint shouldn't be registered when delegate's// disabledreturn getDisabledResponse();}return new NamePatternEnvironmentFilter(this.environment).getResults(name);
}

@ActuatorGetMapping(“/{name:.*}”)与@PathVariable String name –> rest风格,将其name注入到方法的参数name中,匹配规则是任意字符
@ResponseBody –> 返回json格式的数据

@HypermediaDisabled–>表明该MvcEndpoint或者@RequestMapping注解的方法不会生成hypermedia 的响应.代码如下:

@Target({ ElementType.TYPE, ElementType.METHOD })
@Retention(RetentionPolicy.RUNTIME)
@Documented
public @interface HypermediaDisabled {
}

其方法逻辑如下:

如果EnvironmentEndpoint不可用,则返回Disabled Response.

否则实例化NamePatternEnvironmentFilter,调用其getResults方法获得对应name的属性值.

NamePatternEnvironmentFilter继承自NamePatternFilter.

NamePatternFilter:

NamePatternFilter–> 可以使用name正则表达式过滤源数据的实用工具类,用来检测检测名称是否是经典的“single value”键或正则表达式.子类必须实现getValue,getNames 方法.该类是1个泛型类,其泛型参数T 代表着原始数据的类型.

字段,构造器如下:

private static final String[] REGEX_PARTS = { "*", "$", "^", "+", "[" };
private final T source;
NamePatternFilter(T source) {
this.source = source;
}

声明了3个抽象方法:

protected abstract void getNames(T source, NameCallback callback);
protected abstract Object getValue(T source, String name);
protected abstract Object getOptionalValue(T source, String name);

NamePatternFilter中声明了1个方法,代码如下:

public Map<String, Object> getResults(String name) {
// 1. 如果name含有 "*", "$", "^", "+", "[" ,则认为是一个正则表达式,将其返回Pattern.否则返回null
Pattern pattern = compilePatternIfNecessary(name);
if (pattern == null) {
// 2. 如果pattern 等于null,则说明name 是一个普通字符串,调用getValue 这一抽象方法获得value,放入result后返回
Object value = getValue(this.source, name);
Map<String, Object> result = new HashMap<String, Object>();
result.put(name, value);
return result;
}
// 3. 实例化 ResultCollectingNameCallback
ResultCollectingNameCallback resultCollector = new ResultCollectingNameCallback(pattern);
// 4. 抽象方法
getNames(this.source, resultCollector);
// 5, 返回结果
return resultCollector.getResults();
}

如果name含有 “*”, “$”, “^”, “+”, “[” ,则认为是一个正则表达式,将其返回Pattern.否则返回null,代码如下:

private Pattern compilePatternIfNecessary(String name) {
for (String part : REGEX_PARTS) {
if (name.contains(part)) {
try {return Pattern.compile(name);
}
catch (PatternSyntaxException ex) {return null;
}
}
}
return null;
}

如果pattern 等于null,则说明name 是一个普通字符串,调用getValue 这一抽象方法获得value,放入result后返回

实例化 ResultCollectingNameCallback,该类实现了NameCallback接口,该接口只声明了如下方法:

void addName(String name);

ResultCollectingNameCallback中的字段,构造器如下:

// 将name 转换为正则所对应的对象
private final Pattern pattern;
// 结果集
private final Map<String, Object> results = new LinkedHashMap<String, Object>();
ResultCollectingNameCallback(Pattern pattern) {
this.pattern = pattern;
}

其addName方法如下：

public void addName(String name) {
// 1. 如果name 符合正则,则通过调用getOptionalValue 获得值后加入到results
if (this.pattern.matcher(name).matches()) {
Object value = getOptionalValue(NamePatternFilter.this.source, name);
if (value != null) {this.results.put(name, value);
}
}
}

如果name 符合正则,则通过调用getOptionalValue 获得值后加入到results

此外还声明了get方法,来暴露结果集,代码如下:

public Map<String, Object> getResults() {
return this.results;
}

执行getNames方法,进行结果的收集
返回结果

NamePatternEnvironmentFilter

继承了NamePatternFilter 接口,泛型参数为Environment

抽象方法分别实现如下:

getValue:

protected Object getValue(Environment source, String name) {
// 1. 获取值,如果没获取到,则抛出NoSuchPropertyException,否则,对其进行脱敏
Object result = getValue(name);
if (result == null) {
throw new NoSuchPropertyException("No such property: " + name);
}
return ((EnvironmentEndpoint) getDelegate()).sanitize(name, result);
}

调用getValue方法获取值,如果没获取到,则抛出NoSuchPropertyException,否则,对其进行脱敏.

getValue–>直接从environment 中获取值,代码如下:

private Object getValue(String name) {
// 直接从environment 中获取值,
return ((EnvironmentEndpoint) getDelegate()).getResolver().getProperty(name,Object.class);
}

getNames–> 遍历source中的PropertySources,将PropertySource的属性名依次的加入到ResultCollectingNameCallback中.代码如下:

protected void getNames(Environment source, NameCallback callback) {
if (source instanceof ConfigurableEnvironment) {
// 遍历source中的PropertySources,将PropertySource的属性名依次的加入到ResultCollectingNameCallback中
getNames(((ConfigurableEnvironment) source).getPropertySources(),callback);
}
}
private void getNames(PropertySources propertySources, NameCallback callback) {
for (PropertySource<?> propertySource : propertySources) {
if (propertySource instanceof EnumerablePropertySource) {EnumerablePropertySource<?> source = (EnumerablePropertySource<?>) propertySource;for (String name : source.getPropertyNames()) {callback.addName(name);}
}
}
}

getOptionalValue,代码如下:

protected Object getOptionalValue(Environment source, String name) {
// 1. 获得name对应的属性值
Object result = getValue(name);
if (result != null) {
// 2. 如果属性值存在则进行脱敏
result = ((EnvironmentEndpoint) getDelegate()).sanitize(name, result);
}
// 3. 否则直接返回null
return result;
}

获得name对应的属性值
如果属性值存在则进行脱敏
否则直接返回null

属性配置(有@ConfigurationProperties(prefix = “endpoints.env”)注解):
```
endpoints.env.path=/env
```
自动装配:

在EndpointWebMvcManagementContextConfiguration中进行了配置,如下:
```
@Bean
@ConditionalOnMissingBean
@ConditionalOnBean(EnvironmentEndpoint.class)
@ConditionalOnEnabledEndpoint("env")
public EnvironmentMvcEndpoint environmentMvcEndpoint(EnvironmentEndpoint delegate) {return new EnvironmentMvcEndpoint(delegate);
}
```
- @Bean –> 注册1个id为 environmentMvcEndpoint,类型为EnvironmentMvcEndpoint的bean
- @ConditionalOnMissingBean–>BeanFactory中不存在EnvironmentMvcEndpoint类型的bean时生效
- @ConditionalOnBean(EnvironmentEndpoint.class) –> 当BeanFactory中存在EnvironmentEndpoint类型的Bean时生效
- @ConditionalOnEnabledEndpoint(“env”)–> 如果配置有endpoints.env.enabled = true 或者endpoints.enabled= true 则该配置生效.关于此处的实现我们后续有文章进行分析.

LoggersMvcEndpoint

字段,构造器如下:

private final LoggersEndpoint delegate;public LoggersMvcEndpoint(LoggersEndpoint delegate) {super(delegate);this.delegate = delegate;
}

该类声明了2个@ActuatorGetMapping(“/{name:.*}”)注解的方法:

get,代码如下：

@ActuatorGetMapping("/{name:.*}")
@ResponseBody
@HypermediaDisabled
public Object get(@PathVariable String name) {
if (!this.delegate.isEnabled()) {// Shouldn't happen - MVC endpoint shouldn't be registered when delegate's// disabledreturn getDisabledResponse();
}
LoggerLevels levels = this.delegate.invoke(name);
return (levels == null ? ResponseEntity.notFound().build() : levels);
}

@ActuatorGetMapping(“/{name:.*}”) 与 @PathVariable String name–> rest风格,将其name注入到方法的参数name中,匹配规则是任意字符

方法逻辑如下:

如果LoggersEndpoint不可用,则返回默认的不可用消息

否则,调用LoggersEndpoint#invoke 获得LoggerLevels.代码如下:

public LoggerLevels invoke(String name) {
Assert.notNull(name, "Name must not be null");
LoggerConfiguration configuration = this.loggingSystem.getLoggerConfiguration(name);
return (configuration == null ? null : new LoggerLevels(configuration));
}

调用LoggingSystem#getLoggerConfiguration 获得LoggerConfiguration
如果LoggerConfiguration等于null,则返回null,否则,返回LoggerLevels

由于spring boot 默认使用的是logback,因此,此处调用的是LogbackLoggingSystem中的实现,代码如下:

public LoggerConfiguration getLoggerConfiguration(String loggerName) {
return getLoggerConfiguration(getLogger(loggerName));
}

调用getLogger 获得对应的logger,代码如下:

private ch.qos.logback.classic.Logger getLogger(String name) {
LoggerContext factory = getLoggerContext();
if (StringUtils.isEmpty(name) || ROOT_LOGGER_NAME.equals(name)) {
name = Logger.ROOT_LOGGER_NAME;
}
return factory.getLogger(name);
}

获得LoggerContext
如果name为空,或者name等于ROOT,则name赋值为ROOT
根据name获得对应的Logger

调用getLoggerConfiguration获得对应的LoggerConfiguration.

private LoggerConfiguration getLoggerConfiguration(
ch.qos.logback.classic.Logger logger) {
if (logger == null) {
return null;
}
LogLevel level = LEVELS.convertNativeToSystem(logger.getLevel());
LogLevel effectiveLevel = LEVELS
.convertNativeToSystem(logger.getEffectiveLevel());
String name = logger.getName();
if (!StringUtils.hasLength(name) || Logger.ROOT_LOGGER_NAME.equals(name)) {
name = ROOT_LOGGER_NAME;
}
return new LoggerConfiguration(name, level, effectiveLevel);
}

如果logger等于null,返回null
根据logger对应的level,影响的Level分别获得LogLevel
获得logger对应的name,如果name等于null,或者等于root,则将其赋值为root
实例化LoggerConfiguration进行返回

如果 LoggerLevels,则返回ResponseEntity–>状态码为404,否则,直接返回LoggerLevels

set–>该方法用于设置logger的日志级别.代码如下:

@ActuatorPostMapping("/{name:.*}")
@ResponseBody
@HypermediaDisabled
public Object set(@PathVariable String name,@RequestBody Map<String, String> configuration) {
// 1. 如果不可用,则返回默认的不可用信息
if (!this.delegate.isEnabled()) {// Shouldn't happen - MVC endpoint shouldn't be registered when delegate's// disabledreturn getDisabledResponse();
}
// 2. 根据configuration获得LogLevel,然后对指定的logger设置日志级别
LogLevel logLevel = getLogLevel(configuration);
this.delegate.setLogLevel(name, logLevel);
// 3. 返回ok
return ResponseEntity.ok().build();
}

逻辑如下:

如果不可用,则返回默认的不可用信息
根据configuration获得LogLevel,代码如下:
```
private LogLevel getLogLevel(Map<String, String> configuration) {
String level = configuration.get("configuredLevel");
try {
return (level == null ? null : LogLevel.valueOf(level.toUpperCase()));
}
catch (IllegalArgumentException ex) {
throw new InvalidLogLevelException(level);
}
}
```
1. 获得configuredLevel对应的值
2. 如果没有配置,则返回null,否则,返回LogLevel,合法值有TRACE, DEBUG, INFO, WARN, ERROR, FATAL, OFF.如果值不合法,抛出InvalidLogLevelException异常.由于InvalidLogLevelException类注有@ResponseStatus(value = HttpStatus.BAD_REQUEST, reason = “No such log level”),因此,当抛出该异常时,会返回相应的信息.

对指定的logger设置日志级别,代码如下:

public void setLogLevel(String name, LogLevel level) {
Assert.notNull(name, "Name must not be empty");
this.loggingSystem.setLogLevel(name, level);
}

默认情况下,会执行LogbackLoggingSystem#setLogLevel,代码如下:

public void setLogLevel(String loggerName, LogLevel level) {
ch.qos.logback.classic.Logger logger = getLogger(loggerName);
if (logger != null) {
logger.setLevel(LEVELS.convertSystemToNative(level));
}
}

根据对应的logger名获得Logger
将传入的loggerLevel转换为LogBack对应的日志级别
修改日志级别

返回ok

至此,我们明白,要想修改日志级别,可以通过对/loggers/logger名,发送post请求,传入类上如下格式的参数：

{"configuredLevel":"INFO"}

即可修改日志级别

参数配置–>因为该类有@ConfigurationProperties(prefix = “endpoints.loggers”)注解:
```
endpoints.loggers.path=/logfile # Endpoint path
```
自动化装配:

在EndpointWebMvcManagementContextConfiguration中进行了声明,代码如下:
```
@Bean
@ConditionalOnMissingBean
@ConditionalOnBean(LoggersEndpoint.class)
@ConditionalOnEnabledEndpoint("loggers")
public LoggersMvcEndpoint loggersMvcEndpoint(LoggersEndpoint delegate) {return new LoggersMvcEndpoint(delegate);
}
```
- @Bean –> 注册1个id为loggersMvcEndpoint,类型为LoggersMvcEndpoint的bean
- @ConditionalOnMissingBean–> 当BeanFactory中不包含类型为LoggersMvcEndpoint的bean时生效
- @ConditionalOnBean(LoggersEndpoint.class)–> 当BeanFactory中存在LoggersEndpoint类型的bean时生效
- @ConditionalOnEnabledEndpoint(“loggers”)–> 如果配置有endpoints. loggers.enabled = true 或者endpoints.enabled= true 则该配置生效

ShutdownMvcEndpoint

该类继承自EndpointMvcAdapter

构造器如下:

public ShutdownMvcEndpoint(ShutdownEndpoint delegate) {super(delegate);
}

invoke 实现如下:

@PostMapping(produces = { ActuatorMediaTypes.APPLICATION_ACTUATOR_V1_JSON_VALUE,MediaType.APPLICATION_JSON_VALUE })
@ResponseBody
@Override
public Object invoke() {if (!getDelegate().isEnabled()) {return new ResponseEntity<Map<String, String>>(Collections.singletonMap("message", "This endpoint is disabled"),HttpStatus.NOT_FOUND);}return super.invoke();
}

如果ShutdownEndpoint不可用,则返回{message:This endpoint is disabled},否则,调用ShutdownEndpoint#invoke,关闭spring boot 程序

参数配置–> 因为该类声明了@ConfigurationProperties(prefix = “endpoints.shutdown”):
```
endpoints.shutdown.path= # Endpoint path.
```
自动装配:

在EndpointWebMvcManagementContextConfiguration中进行了声明,代码如下:
```
@Bean
@ConditionalOnMissingBean
@ConditionalOnBean(ShutdownEndpoint.class)
@ConditionalOnEnabledEndpoint(value = "shutdown", enabledByDefault = false)
public ShutdownMvcEndpoint shutdownMvcEndpoint(ShutdownEndpoint delegate) {return new ShutdownMvcEndpoint(delegate);
}
```
- @Bean –> 注册1个id为shutdownMvcEndpoint,类型为ShutdownMvcEndpoint的bean
- @ConditionalOnMissingBean–> 当BeanFactory中不包含类型为ShutdownMvcEndpoint的bean时生效
- @ConditionalOnBean(ShutdownEndpoint.class)–> 当BeanFactory中存在ShutdownEndpoint类型的bean时生效
- @ConditionalOnEnabledEndpoint(“shutdown”, enabledByDefault = false) –>如果配置有endpoints. shutdown.enabled = true则该配置生效,如果没有配置,该配置不生效

MetricsMvcEndpoint

MetricsMvcEndpoint–> 继承自EndpointMvcAdapter.

字段构造器如下:

private final MetricsEndpoint delegate;public MetricsMvcEndpoint(MetricsEndpoint delegate) {super(delegate);this.delegate = delegate;
}

该类声明了1个被@ActuatorGetMapping注解的方法,如下:

@ActuatorGetMapping("/{name:.*}")
@ResponseBody
@HypermediaDisabled
public Object value(@PathVariable String name) {if (!this.delegate.isEnabled()) {return getDisabledResponse();}return new NamePatternMapFilter(this.delegate.invoke()).getResults(name);
}

如果不可用,则返回默认的不可用信息
实例化NamePatternMapFilter ,之后调用其getResults方法,根据传入的name 获得对应的map,key –>name,value–>name所对应的Metric的值

NamePatternMapFilter:
1. 继承了NamePatternFilter 接口,泛型参数为Map
2. 抽象方法实现如下:
  1. getValue–> 调用getOptionalValue获得MetricsEndpoint中Metrics名字为传入的值所对应的Metrics的值.,如果获取不到,则抛出NoSuchMetricException.代码如下:
```
protected Object getValue(Map<String, ?> source, String name) {Object value = getOptionalValue(source, name);if (value == null) {throw new NoSuchMetricException("No such metric: " + name);}return value;
}
```
    NoSuchMetricException代码如下:
```
@ResponseStatus(value = HttpStatus.NOT_FOUND, reason = "No such metric")
public static class NoSuchMetricException extends RuntimeException {public NoSuchMetricException(String string) {super(string);}}
```
    当抛出该异常时,返回的状态码为404,reason为No such metric
  2. getOptionalValue–> 获得MetricsEndpoint中Metrics名字为传入的值所对应的Metrics的值.代码如下:
```
protected Object getOptionalValue(Map<String, ?> source, String name) {return source.get(name);
}
```
  3. getNames–>遍历MetricsEndpoint中返回的Metrics名,如果Metrics名符合正则的话(MetricsMvcEndpoint#value方法传入的是正则),则加入到ResultCollectingNameCallback的result中.代码如下:
```
protected void getNames(Map<String, ?> source, NameCallback callback) {for (String name : source.keySet()) {try {callback.addName(name);}catch (NoSuchMetricException ex) {// Metric with null value. Continue.}}
}
```

自动装配:

声明在EndpointWebMvcManagementContextConfiguration中.代码如下:
```
@Bean
@ConditionalOnMissingBean
@ConditionalOnBean(MetricsEndpoint.class)
@ConditionalOnEnabledEndpoint("metrics")
public MetricsMvcEndpoint metricsMvcEndpoint(MetricsEndpoint delegate) {return new MetricsMvcEndpoint(delegate);
}
```
- @Bean –> 注册1个id为metricsMvcEndpoint,类型为MetricsMvcEndpoint的bean
- @ConditionalOnMissingBean–> BeanFactory中不存在MetricsMvcEndpoint类型的bean时生效
- @ConditionalOnBean(MetricsEndpoint.class)–> BeanFactory中存在MetricsEndpoint类型的bean时生效
- @ConditionalOnEnabledEndpoint(“metrics”) –> 如果配置有endpoints. metrics.enabled = true 或者endpoints.enabled= true 则该配置生效