使用Spring Boot如何实现配置数据库链接池？相信很多没有经验的人对此束手无策，为此本文总结了问题出现的原因和解决方法，通过这篇文章希望你能解决这个问题。

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配置方法

基于当前的1.5.2.RELEASE的Spring Boot。

依照官方文档，如果增加了如下依赖的配置，或者类路径中存在spring-boot-starter-jdbc的jar，那么已默认启用了数据库链接池。

 
  org.springframework.boot
  spring-boot-starter-jdbc
 

Spring Boot选择数据库链接池实现的判断逻辑：

1.检查Tomcat的数据库链接池实现是否可用，如可用，则启用。使用spring.datasource.tomcat.*可以控制链接池的行为。

2.检查HikariCP是否可用，如可用，则启用。使用spring.datasource.hikari.*可以控制链接池的行为。

3.检查Commons DBCP是否可用，如可用，则启用；但Spring Boot不建议在生产环境使用该链接池的实现。

4.检查Commons DBCP2是否可用，如可用，则启用。使用spring.datasource.dbcp2.*可以控制链接池的行为。

使用tomcat-jdbc时，可在application.yml增加配置项spring.datasource.tomcat.*来控制链接池的行为。比如如下配置。

spring:

datasource:
  url: jdbc:MySQL://localhost:3306/jackieathome?useSSL=false
  username: root
  password: mypassword
  # 6.x版本的MySQL JDBC驱动类为com.mysql.cj.jdbc.Driver
  # 5.X版本的MySQL JDBC驱动类为com.mysql.jdbc.Driver
  driver-class-name: com.mysql.cj.jdbc.Driver
  tomcat:
   max-wait: 10000
   max-active: 30
   test-on-borrow: true
   # 传递MySQL JDBC特有的参数
   db-properties:
    logger: net.jackieathome.db.customized.MySQLLogger
    gatherPerfMetrics: 'true'
    profileSQL: 'true'
    reportMetricsIntervalMillis: '60000'
    logSlowQueries: 'true'
    explainSlowQueries: 'true'

    logging:

 level:
  # 关闭其它软件的日志，减少干扰
  org: ERROR
  net: ERROR
  com: ERROR
  # 开启MySQL JDBC驱动的日志
  MySQL: DEBUG

上述spring.datasource.tomcat.*代表的配置项，可参考tomcat-jdbc的官方文档Apache Tomcat 8.5 - The Tomcat JDBC Connection Pool或者Apache Tomcat 8.0 - The Tomcat JDBC Connection Pool。

依据tomcat-jdbc的文档，如需要向数据库的JDBC驱动传入控制参数，可以使用db-properties字段。需要注意的是，当使用MySQL驱动时，控制参数的值需要强制转换为字符串，否则创建数据库链接时会报错。配置方法如上述样例中的 reportMetricsIntervalMillis: '60000'和logSlowQueries: 'true'。

依照MySQL JDBC驱动文档，可以配置一个日志记录器，用于记录其工作时的输出，如下是实现样例。

package net.jackieathome.db.customized;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;
public class MySQLLogger implements com.mysql.cj.api.log.Log {
  private static Logger LOG;
  public MySQLLogger(String name) {
    LOG = LoggerFactory.getLogger(name);
  }
  @Override
  public boolean isDebugEnabled() {
    return LOG.isDebugEnabled();
  }
  @Override
  public boolean isErrorEnabled() {
    return LOG.isErrorEnabled();
  }
  @Override
  public boolean isFatalEnabled() {
    return LOG.isErrorEnabled();
  }
  @Override
  public boolean isInfoEnabled() {
    return LOG.isInfoEnabled();
  }
  @Override
  public boolean isTraceEnabled() {
    return LOG.isTraceEnabled();
  }
  @Override
  public boolean isWarnEnabled() {
    return LOG.isWarnEnabled();
  }
  @Override
  public void logDebug(Object msg) {
    LOG.debug("{}", msg);
  }
  @Override
  public void logDebug(Object msg, Throwable thrown) {
    LOG.debug("{}", msg, thrown);
  }
  @Override
  public void logError(Object msg) {
    LOG.error("{}", msg);
  }
  @Override
  public void logError(Object msg, Throwable thrown) {
    LOG.error("{}", msg, thrown);
  }
  @Override
  public void logFatal(Object msg) {
    LOG.error("{}", msg);
  }
  @Override
  public void logFatal(Object msg, Throwable thrown) {
    LOG.error("{}", msg, thrown);
  }
  @Override
  public void logInfo(Object msg) {
    LOG.info("{}", msg);
  }
  @Override
  public void logInfo(Object msg, Throwable thrown) {
    LOG.info("{}", msg, thrown);
  }
  @Override
  public void logTrace(Object msg) {
    LOG.trace("{}", msg);
  }
  @Override
  public void logTrace(Object msg, Throwable thrown) {
    LOG.trace("{}", msg, thrown);
  }
  @Override
  public void logWarn(Object msg) {
    LOG.warn("{}", msg);
  }
  @Override
  public void logWarn(Object msg, Throwable thrown) {
    LOG.warn("{}", msg, thrown);
  }
}

同时修改application.yml，增加相应的日志配置，如下。

logging:
  level:
    # 开启MySQL JDBC驱动的日志
    MySQL: DEBUG

如下是MySQL JDBC驱动输出的样例日志。

2017-04-16 00:51:32.626 QUERY created: Sun Apr 16 00:51:32 CST 2017 duration: 0 connection: 93 statement: 1 resultset: 1 message: /* mysql-connector-java-6.0.6 ( Revision: 3dab84f4d9bede3cdd14d57b99e9e98a02a5b97d ) */SELECT  @@session.auto_increment_increment AS auto_increment_increment, @@character_set_client AS character_set_client, @@character_set_connection AS character_set_connection, @@character_set_results AS character_set_results, @@character_set_server AS character_set_server, @@init_connect AS init_connect, @@interactive_timeout AS interactive_timeout, @@license AS license, @@lower_case_table_names AS lower_case_table_names, @@max_allowed_packet AS max_allowed_packet, @@net_buffer_length AS net_buffer_length, @@net_write_timeout AS net_write_timeout, @@query_cache_size AS query_cache_size, @@query_cache_type AS query_cache_type, @@sql_mode AS sql_mode, @@system_time_zone AS system_time_zone, @@time_zone AS time_zone, @@tx_isolation AS tx_isolation, @@wait_timeout AS wait_timeout
2017-04-16 00:51:32.629 FETCH created: Sun Apr 16 00:51:32 CST 2017 duration: 36 connection: 93 statement: 1 resultset: 1
2017-04-16 00:51:32.639 QUERY created: Sun Apr 16 00:51:32 CST 2017 duration: 1 connection: 93 statement: 999 resultset: 0 message: SET NAMES latin1
2017-04-16 00:51:32.640 FETCH created: Sun Apr 16 00:51:32 CST 2017 duration: 0 connection: 93 statement: 999 resultset: 0
2017-04-16 00:51:32.642 QUERY created: Sun Apr 16 00:51:32 CST 2017 duration: 2 connection: 93 statement: 999 resultset: 0 message: SET character_set_results = NULL
2017-04-16 00:51:32.643 FETCH created: Sun Apr 16 00:51:32 CST 2017 duration: 0 connection: 93 statement: 999 resultset: 0
2017-04-16 00:51:32.645 QUERY created: Sun Apr 16 00:51:32 CST 2017 duration: 0 connection: 93 statement: 999 resultset: 0 message: SET autocommit=1
2017-04-16 00:51:32.646 FETCH created: Sun Apr 16 00:51:32 CST 2017 duration: 0 connection: 93 statement: 999 resultset: 0
2017-04-16 00:51:32.667 QUERY created: Sun Apr 16 00:51:32 CST 2017 duration: 1 connection: 94 statement: 2 resultset: 2 message: /* mysql-connector-java-6.0.6 ( Revision: 3dab84f4d9bede3cdd14d57b99e9e98a02a5b97d ) */SELECT  @@session.auto_increment_increment AS auto_increment_increment, @@character_set_client AS character_set_client, @@character_set_connection AS character_set_connection, @@character_set_results AS character_set_results, @@character_set_server AS character_set_server, @@init_connect AS init_connect, @@interactive_timeout AS interactive_timeout, @@license AS license, @@lower_case_table_names AS lower_case_table_names, @@max_allowed_packet AS max_allowed_packet, @@net_buffer_length AS net_buffer_length, @@net_write_timeout AS net_write_timeout, @@query_cache_size AS query_cache_size, @@query_cache_type AS query_cache_type, @@sql_mode AS sql_mode, @@system_time_zone AS system_time_zone, @@time_zone AS time_zone, @@tx_isolation AS tx_isolation, @@wait_timeout AS wait_timeout

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