我们知道health端点用于查看Spring Boot应用的健康状态，提供了用于检测磁盘的DiskSpaceHealthIndicator、检测DataSource连接是否可用的DataSourceHealthIndicator、检测XXX内置服务（XXX代表内置的Elasticsearch、JMS、Mail、MongoDB、Rabbit、Redis、Solr等）是否可用的XXXHealthIndicator等健康指标检测器。在Spring Boot中，这些检测器都是通过HealthIndicator接口实现，并且根据依赖关系的引入实现自动化装配。
    当Spring Boot自带的HealthIndicator接口实现类不能满足我们的需求时，就需要自定义HealthIndicator接口实现类。自定义HealthIndicator接口实现类很简单，只需要实现HealthIndicator接口，并重写接口方法health，返回一个Health对象。

自定义HealthIndicator

1．创建HealthIndicator接口实现类MyHealthIndicator
2．将健康详细信息显示给所有用户
3．测试运行

<project xmlns="http://maven.apache.org/POM/4.0.0" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd">
  <modelVersion>4.0.0</modelVersion>
  <groupId>com.health</groupId>
  <artifactId>SpringBootHealthIndicator</artifactId>
  <version>0.0.1-SNAPSHOT</version>
  
  <parent>
        <groupId>org.springframework.boot</groupId>
        <artifactId>spring-boot-starter-parent</artifactId>
        <version>2.0.0.RELEASE</version>
        <relativePath /> <!-- lookup parent from repository -->
    </parent>

    <properties>
        <!-- 声明项目配置依赖编码格式为 utf-8 -->
        <project.build.sourceEncoding>UTF-8</project.build.sourceEncoding>
        <project.reporting.outputEncoding>UTF-8</project.reporting.outputEncoding>
        <fastjson.version>1.2.24</fastjson.version>
    </properties>

    <dependencies>
        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter-actuator</artifactId>
        </dependency>
        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter-data-jpa</artifactId>
        </dependency>

        <!-- 添加MySQL依赖 -->
        <dependency>
            <groupId>mysql</groupId>
            <artifactId>mysql-connector-java</artifactId>
            <scope>runtime</scope>
            <version>8.0.13</version><!--$NO-MVN-MAN-VER$ -->
        </dependency>

        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter-web</artifactId>
        </dependency>
        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter-test</artifactId>
            <scope>test</scope>
        </dependency>
    </dependencies>
  
  <build>
    <plugins>
      <plugin>
        <artifactId>maven-compiler-plugin</artifactId>
        <configuration>
          <source>1.8</source>
          <target>1.8</target>
        </configuration>
      </plugin>
    </plugins>
  </build>
</project>

spring.datasource.url=jdbc:mysql://localhost:3306/springbootjpa?serverTimezone=UTC&autoReconnect=true
spring.datasource.username=root
spring.datasource.password=admin
spring.datasource.driver-class-name=com.mysql.cj.jdbc.Driver
spring.jpa.database=MYSQL
spring.jpa.show-sql=true
spring.jpa.hibernate.ddl-auto=update
spring.jackson.serialization.indent-output=true
management.endpoints.web.exposure.include=*
management.endpoint.health.show-details=always

package com.ch.ch10_2.health;

import org.springframework.boot.actuate.health.Health;
import org.springframework.boot.actuate.health.HealthIndicator;
import org.springframework.stereotype.Component;

@Component
public class MyHealthIndicator implements HealthIndicator {
    @Override
    public Health health() {
        int errorCode = check();
        if (errorCode != 0) {
            // down方法表示异常，withDetail方法添加任意多的异常信息
            return Health.down().withDetail("message", "error:" + errorCode).build();
        }
        // up方法表示健康
        return Health.up().build();
    }

    /**
     * 模拟返回一个错误状态
     */
    private int check() {
        return 1;
    }
}

2．将健康详细信息显示给所有用户

在配置文件application.properties中，配置将详细健康信息显示给所有用户。配置内容如下：
#将详细健康信息显示给所有用户
management.endpoint.health.show-details=always

3．测试运行

health的对象名默认为类名去掉HealthIndicator后缀，并且首字母小写，因此该例的health对象名为my。
启动应用程序主类Ch102Application，并通过“http://localhost:8080/actuator/health/my”测试运行

package com.ch.ch10_2;

import org.springframework.boot.SpringApplication;
import org.springframework.boot.autoconfigure.SpringBootApplication;

@SpringBootApplication
public class Ch102Application {
    public static void main(String[] args) {
        SpringApplication.run(Ch102Application.class, args);
    }
}

package com.ch.ch10_2.endPoint;

import java.util.HashMap;
import java.util.Map;
import org.springframework.boot.actuate.endpoint.annotation.Endpoint;
import org.springframework.boot.actuate.endpoint.annotation.ReadOperation;
import org.springframework.boot.actuate.endpoint.annotation.WriteOperation;
import org.springframework.stereotype.Component;
import com.zaxxer.hikari.HikariConfigMXBean;
import com.zaxxer.hikari.HikariDataSource;
import com.zaxxer.hikari.HikariPoolMXBean;

//注册为端点，id不能使用驼峰法（dataSource），需要以-分割
@Endpoint(id = "data-source")
@Component
public class DataSourceEndpoint {
    // HikariDataSource提供多个监控信息
    HikariDataSource ds;

    public DataSourceEndpoint(HikariDataSource ds) {
        this.ds = ds;
    }

    @ReadOperation
    public Map<String, Object> info() {
        Map<String, Object> map = new HashMap<String, Object>();
        // 连接池配置
        HikariConfigMXBean configBean = ds.getHikariConfigMXBean();
        map.put("max", configBean.getMaximumPoolSize());
        // 连接池运行状态
        HikariPoolMXBean mxBean = ds.getHikariPoolMXBean();
        map.put("active", mxBean.getActiveConnections());
        map.put("idle", mxBean.getIdleConnections());
        // 连接池无连接时，等待获取连接的线程个数
        map.put("wait", mxBean.getThreadsAwaitingConnection());
        return map;
    }

    @WriteOperation
    public void setMax(int max) {
        ds.getHikariConfigMXBean().setMaximumPoolSize(max);
    }
}

package com.ch.ch10_2;

import org.junit.Test;
import org.junit.runner.RunWith;
import org.springframework.boot.test.context.SpringBootTest;
import org.springframework.test.context.junit4.SpringRunner;

@RunWith(SpringRunner.class)
@SpringBootTest
public class Ch102ApplicationTests {
    @Test
    public void contextLoads() {
    }
}