配置方法

基於當前的1.5.2.RELEASE的Spring Boot。 依照官方文件，如果增加了如下依賴的配置，或者類路徑中存在spring-boot-starter-jdbc的jar，那麼已預設啟用了資料庫連結池。

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

Spring Boot選擇資料庫連結池實現的判斷邏輯：

1. 檢查Tomcat的資料庫連結池實現是否可用，如可用，則啟用。使用spring.datasource.tomcat.*
   可以控制連結池的行為。
2. 檢查HikariCP是否可用，如可用，則啟用。使用spring.datasource.hikari.*可以控制連結池的行為。
3. 檢查Commons DBCP是否可用，如可用，則啟用；但Spring Boot不建議在生產環境使用該連結池的實現。
4. 檢查Commons DBCP2是否可用，如可用，則啟用。使用spring.datasource.dbcp2.*可以控制連結池的行為。

使用tomcat-jdbc時，可在application.yml增加配置項spring.datasource.tomcat.*來控制連結池的行為。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驅動類為com.mysql.cj.jdbc.Driver
        # 5.X版本的MySQL JDBC驅動類為com.mysql.jdbc.Driver
        driver-class-name: com.mysql.cj.jdbc.Driver
        tomcat:
            max-wait: 10000
            max-active: 30
            test-on-borrow: true
            # 傳遞MySQL JDBC特有的引數
            db-properties:
                logger: net.jackieathome.db.customized.MySQLLogger
                gatherPerfMetrics: 'true'
                profileSQL: 'true'
                reportMetricsIntervalMillis: '60000'
                logSlowQueries: 'true'
                explainSlowQueries: 'true'
logging:
    level:
        # 關閉其它軟體的日誌，減少干擾
        org: ERROR
        net: ERROR
        com: ERROR
        # 開啟MySQL JDBC驅動的日誌
        MySQL: DEBUG
 

上述spring.datasource.tomcat.*代表的配置項，可參考tomcat-jdbc的官方文件Apache Tomcat 8.5 - The Tomcat JDBC Connection Pool或者Apache Tomcat 8.0 - The Tomcat JDBC Connection Pool。 依據tomcat-jdbc的文件，如需要向資料庫的JDBC驅動傳入控制引數，可以使用db-properties欄位。需要注意的是，當使用MySQL驅動時，控制引數的值需要強制轉換為字串，否則建立資料庫連結時會報錯。配置方法如上述樣例中的 reportMetricsIntervalMillis: '60000'和logSlowQueries: 'true'。 依照MySQL JDBC驅動文件，可以配置一個日誌記錄器，用於記錄其工作時的輸出，如下是實現樣例。

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);
    }
}

同時修改application.yml，增加相應的日誌配置，如下。

logging:
    level:
        # 開啟MySQL JDBC驅動的日誌
        MySQL: DEBUG

如下是MySQL JDBC驅動輸出的樣例日誌。

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

參考資料

Spring的連結池配置

Spring Boot的連結池的配置

Tomcat的連結池的配置

MySQL JDBC

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