开发中使用Consul作为服务注册中心时，项目接入sharding-jdbc后，db测活一致失败问题解决

一、问题背景：

项目中（Spring boot）使用consul作为服务注册中心时，当接入sharding-jdbc 1.4.x版本后，健康检查一直失败。主要是db检测失败，抛出以下错误：

"db": {
"status": "DOWN",
"database": "MySQL",
"error": "java.lang.NullPointerException: null"
}

二、问题分析：

1.Consul中的测活依赖于spring-boot-starter-actuator包，不添加会check failing；

 
    org.springframework.boot 
    spring-boot-starter-actuator 

2.在actuator包中下面HealthIndicators会被Spring Boot自动配置：

名字	描述
CassandraHealthIndicator	检查Cassandra database是否正常
DiskSpaceHealthIndicator	低磁盘空间检测
DataSourceHealthIndicator	检查数据库连接是否正常
ElasticsearchHealthIndicator	检查Elasticsearch cluster是否正常
JmsHealthIndicator	检查JMS broker是否正常
MailHealthIndicator	检查mail server是否正常
MongoHealthIndicator	检查Mongo database是否正常
RabbitHealthIndicator	检查Rabbit server是否正常
RedisHealthIndicator	检查Redis server是否正常
SolrHealthIndicator	检查Solr server是否正常

3.该问题主要是在执行DataSourceHealthIndicator时，报错。

dbHealthIndicator自动注册部分的源码：

//org.springframework.boot.actuate.autoconfigure.HealthIndicatorAutoConfiguration 类中定义
//....
@Bean
@ConditionalOnMissingBean(name = "dbHealthIndicator")
public HealthIndicator dbHealthIndicator() {
   return createHealthIndicator(this.dataSources);
}

@Override
protected DataSourceHealthIndicator createHealthIndicator(DataSource source) {
   return new DataSourceHealthIndicator(source, getValidationQuery(source));
}

private String getValidationQuery(DataSource source) {
   DataSourcePoolMetadata poolMetadata = this.poolMetadataProvider
         .getDataSourcePoolMetadata(source);
   return (poolMetadata == null ? null : poolMetadata.getValidationQuery());
}

DataSourceHealthIndicator的数据库检测部分源码：

//类
//org.springframework.boot.actuate.health.DataSourceHealthIndicator

//...

@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 {
		String product = getProduct();
		builder.up().withDetail("database", product);
		String validationQuery = getValidationQuery(product);
		if (StringUtils.hasText(validationQuery)) {
			try {
				// Avoid calling getObject as it breaks MySQL on Java 7
				List