Tomcat 中的 JDBC Pool

摘要：连接池的名称指定由连接池所创建的连接的自动提交状态。由连接池所创建的连接对数据库的只读属性指定由连接池所创建的连接的事务级别。以毫秒表示的当连接池中没有可用连接时等待可用连接返回的时间，超时则抛出异常，值为时无限期等待。

什么是 Connection Pool -- 连接池呢？

我就不解释了。不太清楚的看这篇文章 [生产级别Nodejs开发实践-使用连接池]（这篇文章的前半部分讲述了什么是连接池）

它的英文文档在：[The Tomcat JDBC Connection Pool]

Tomcat 不仅是非常受欢迎的 Servlet 容器，也是同时为我们提供了很多非常实用组件。 jdbc pool 就是其中一个非常实用且高效的 jdbc 连接池的实现. Tomcat 官方大概列出了15条tomcat相对于其他连接池的优点，我这里就不在详细解释了。

jdbc pool 组件存在于 tomcat8 release 版本的 lib/tomcat-jdbc.jar 包中。

我们所使用的到所有类都存在于 org.apache.tomcat.jdbc.pool 包名下。

这里面我们以 mysql 作为数据库来演示
添加 mysql-connector 依赖

xml
    mysql
    mysql-connector-java
    5.1.34

xml
    org.apache.tomcat
    tomcat-jdbc
    8.0.15

javaimport java.sql.Connection;
import java.sql.PreparedStatement;
import java.sql.ResultSet;
import java.sql.SQLException;

import org.apache.tomcat.jdbc.pool.DataSource;
import org.apache.tomcat.jdbc.pool.PoolProperties;

// main
// 创建连接池属性对象
PoolProperties poolProps = new PoolProperties();
poolProps.setUrl("jdbc:mysql://localhost:3306/test");

poolProps.setDriverClassName("com.mysql.jdbc.Driver");

poolProps.setUsername("root");

poolProps.setPassword("123456");

// 创建连接池, 使用了 tomcat 提供的的实现，它实现了 javax.sql.DataSource 接口
DataSource dataSource = new DataSource();
// 为连接池设置属性
dataSource.setPoolProperties(poolProps);

try (Connection conn = dataSource.getConnection()) {

    PreparedStatement state = conn.prepareStatement("select * from book");

    ResultSet result = state.executeQuery();

    StringBuilder stringBuilder = new StringBuilder();

    while ( result.next() ) {
            stringBuilder.append("[ id: "+ result.getInt("id") + ", ").append("name: " + result.getString("name") + ",	").append("publisher: " + result.getString("publisher")).append(" ]
");
    }

    System.out.println(stringBuilder.toString());

} 
catch (SQLException e) 
{
    e.printStackTrace();
}

java    private volatile Properties dbProperties = new Properties();
    private volatile String url = null;
    private volatile String driverClassName = null;
    private volatile Boolean defaultAutoCommit = null;
    private volatile Boolean defaultReadOnly = null;
    private volatile int defaultTransactionIsolation = DataSourceFactory.UNKNOWN_TRANSACTIONISOLATION;
    private volatile String defaultCatalog = null;
    private volatile String connectionProperties;
    private volatile int initialSize = 10;
    private volatile int maxActive = DEFAULT_MAX_ACTIVE;
    private volatile int maxIdle = maxActive;
    private volatile int minIdle = initialSize;
    private volatile int maxWait = 30000;
    private volatile String validationQuery;
    private volatile int validationQueryTimeout = -1;
    private volatile String validatorClassName;
    private volatile Validator validator;
    private volatile boolean testOnBorrow = false;
    private volatile boolean testOnReturn = false;
    private volatile boolean testWhileIdle = false;
    private volatile int timeBetweenEvictionRunsMillis = 5000;
    private volatile int numTestsPerEvictionRun;
    private volatile int minEvictableIdleTimeMillis = 60000;
    private volatile boolean accessToUnderlyingConnectionAllowed = true;
    private volatile boolean removeAbandoned = false;
    private volatile int removeAbandonedTimeout = 60;
    private volatile boolean logAbandoned = false;
    private volatile String name = "Tomcat Connection Pool["+(poolCounter.addAndGet(1))+"-"+System.identityHashCode(PoolProperties.class)+"]";
    private volatile String password;
    private volatile String username;
    private volatile long validationInterval = 30000;
    private volatile boolean jmxEnabled = true;
    private volatile String initSQL;
    private volatile boolean testOnConnect =false;
    private volatile String jdbcInterceptors=null;
    private volatile boolean fairQueue = true;
    private volatile boolean useEquals = true;
    private volatile int abandonWhenPercentageFull = 0;
    private volatile long maxAge = 0;
    private volatile boolean useLock = false;
    private volatile InterceptorDefinition[] interceptors = null;
    private volatile int suspectTimeout = 0;
    private volatile Object dataSource = null;
    private volatile String dataSourceJNDI = null;
    private volatile boolean alternateUsernameAllowed = false;
    private volatile boolean commitOnReturn = false;
    private volatile boolean rollbackOnReturn = false;
    private volatile boolean useDisposableConnectionFacade = true;
    private volatile boolean logValidationErrors = false;
    private volatile boolean propagateInterruptState = false;
    private volatile boolean ignoreExceptionOnPreLoad = false;

javapoolProps.setJdbcInterceptors("org.apache.tomcat.jdbc.pool.interceptor.ConnectionState;org.apache.tomcat.jdbc.pool.interceptor.StatementFinalizer");