01-如何在 Spring Boot 应用程序中使用 Actuator 监控和管理端点，提高应用程序的生产力？

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

13:15:17.642 ifp [main] INFO  o.s.b.a.e.web.EndpointLinksResolver - Exposing 2 endpoint(s) beneath base path '/actuator'
13:15:17.654 ifp [main] INFO  o.s.b.a.e.w.s.WebMvcEndpointHandlerMapping - Mapped "{[/actuator/health],methods=[GET],produces=[application/vnd.spring-boot.actuator.v2+json || application/json]}" onto public java.lang.Object org.springframework.boot.actuate.endpoint.web.servlet.AbstractWebMvcEndpointHandlerMapping$OperationHandler.handle(javax.servlet.http.HttpServletRequest,java.util.Map<java.lang.String, java.lang.String>)
13:15:17.655 ifp [main] INFO  o.s.b.a.e.w.s.WebMvcEndpointHandlerMapping - Mapped "{[/actuator/info],methods=[GET],produces=[application/vnd.spring-boot.actuator.v2+json || application/json]}" onto public java.lang.Object org.springframework.boot.actuate.endpoint.web.servlet.AbstractWebMvcEndpointHandlerMapping$OperationHandler.handle(javax.servlet.http.HttpServletRequest,java.util.Map<java.lang.String, java.lang.String>)
13:15:17.656 ifp [main] INFO  o.s.b.a.e.w.s.WebMvcEndpointHandlerMapping - Mapped "{[/actuator],methods=[GET],produces=[application/vnd.spring-boot.actuator.v2+json || application/json]}" onto protected java.util.Map<java.lang.String, java.util.Map<java.lang.String, org.springframework.boot.actuate.endpoint.web.Link>> org.springframework.boot.actuate.endpoint.web.servlet.WebMvcEndpointHandlerMapping.links(javax.servlet.http.HttpServletRequest,javax.servlet.http.HttpServletResponse)

{
    "_links": {
        "self": {
            "href": "http://localhost:19086/actuator",
            "templated": false
        },
        "health": {
            "href": "http://localhost:19086/actuator/health",
            "templated": false
        },
        "info": {
            "href": "http://localhost:19086/actuator/info",
            "templated": false
        }
    }
}

http://localhost:19086/actuator/health：

{
	"status": "UP"
}

management:
  endpoints:
    web:
      exposure:
        include: '*'

package org.springframework.boot.actuate.health;

/**
 * 这个接口可以通过某种策略来判断程序应用的健康状况
 *
 * @author Dave Syer
 * @see ApplicationHealthIndicator
 */
@FunctionalInterface
public interface HealthIndicator {

	/**
	 * 返回健康状况的指示
	 * 这个指示可以告诉程序用户或管理员系统的健康程度，以供后续决策和操作。
	 */
	Health health();

}

@JsonInclude(Include.NON_EMPTY)
public final class Health {

	private final Status status;

	private final Map<String, Object> details;
  ...
}

management:
  endpoint:
    health:
      show-details: always

http://localhost:19086/actuator/health

{
    "status": "UP",
    "details": {
        "diskSpace": {
            "status": "UP",
            "details": {
                "total": 499963174912,
                "free": 22110871552,
                "threshold": 10485760
            }
        },
        "db": {
            "status": "UP",
            "details": {
                "database": "MySQL",
                "hello": 1
            }
        }
    }
}

	@Override
	protected void doHealthCheck(Health.Builder builder) throws Exception {
		if (this.dataSource == null) {
			builder.up().withDetail("database", "unknown");
		}
		else {
			doDataSourceHealthCheck(builder);
		}
	}

private void doDataSourceHealthCheck(Health.Builder builder) throws Exception {
  // ①
  String product = getProduct();
  // 就开始拼接要输出的信息了
  builder.up().withDetail("database", product);
  // ②
  String validationQuery = getValidationQuery(product);
  if (StringUtils.hasText(validationQuery)) {
    // Avoid calling getObject as it breaks MySQL on Java 7
    List<Object> results = this.jdbcTemplate.query(validationQuery,
        new SingleColumnRowMapper());
    // ③
    Object result = DataAccessUtils.requiredSingleResult(results);
    builder.withDetail("hello", result);
  }
}

String product = getProduct();

private String getProduct() {
  return this.jdbcTemplate.execute((ConnectionCallback<String>) this::getProduct);
}

private String getProduct(Connection connection) throws SQLException {
  return connection.getMetaData().getDatabaseProductName();
}

info:
  project-name: car-receiver
  author: JavaEdge
  app:
    encoding: UTF-8
    java:
      source: 1.8
      target: 1.8

info.app.encoding=@project.build.sourceEncoding@
info.app.java.source=@java.version@
info.app.java.target=@java.version@

management.info.git.mode=full