ConnectionPool.java

package com.github.walker.easydb.connection;

import com.github.walker.easydb.assistant.EasyConfig;
import com.github.walker.easydb.assistant.LogFactory;
import com.github.walker.easydb.exception.DataAccessException;
import org.apache.log4j.Logger;

import java.sql.Connection;
import java.sql.ResultSet;
import java.sql.SQLException;
import java.sql.Statement;
import java.util.HashMap;

/**
 * Connecion pool, it responsibles for geting and recycling the connecions.
 * Class EasyDBConnPool and ServerConnPool implemented it.
 *
 * @author HuQingmiao
 */
public abstract class ConnectionPool {

    protected static Logger log = LogFactory.getLogger(ConnectionPool.class);

    // instance pool
    private static HashMap<String, ConnectionPool> instances = new HashMap<String, ConnectionPool>(3);

    /**
     * Gets the default instance of this class. This method decides which
     * connection pool to be adopted. The ServerConnPool is prior to the
     * EasyDBConnPool.<br>
     * <p/>
     * 取得连接池的默认方法, 该方法试图取得与"jndi.name"相应的连接池, 如果没有在配置文件中 设定"jndi.name"的相应值,
     * 则获取EasyDB自实现的连接池.
     *
     * @return the instace of subclass .
     */
    public synchronized static ConnectionPool getInstance() {

        // 默认的JNDI键名采用"jndi.name"
        return getInstance("jndi.name");
    }

    /**
     * 获取数据库类型
     *
     * @return 数据库类型, 如'mysql', 'oracle'
     */
    public abstract String getDBType();

    /**
     * 取得指定jndi键名对应的连接池.
     *
     * @return the instace of subclass .
     */
    public synchronized static ConnectionPool getInstance(String jndiKey) {

        String jndiName = EasyConfig.getProperty(jndiKey);

        // 如果配置文件中为jndi.name设置了值, 则采用web服务器的连接池
        if (jndiName != null && !"".equals(jndiName.trim())) {
            if (instances.containsKey(jndiName)) {
                return instances.get(jndiName);
            } else {
                ConnectionPool instance = new ServerConnPool(jndiKey);
                instances.put(jndiName, instance);
                return instance;
            }

            // 采用自实现的连接池
        } else {
            if (instances.containsKey("NO_JNDI")) {
                return instances.get("NO_JNDI");

            } else {
                String driverStr = EasyConfig.getProperty("driverStr");
                String dataSource = EasyConfig.getProperty("dataSource");
                String username = EasyConfig.getProperty("username");

                if (driverStr != null && dataSource != null && username != null) {
                    ConnectionPool instance = new EasyDBConnPool();
                    instances.put("NO_JNDI", instance);
                    return instance;
                }

                // 没有找到数据库的配置信息
                String errorMsg = "Getting the database configuration... FAILED!  Please check the file '"
                        + EasyConfig.CONFIG_FILENAME + "'. ";
                log.error(errorMsg);

                return null;
            }
        }
    }

    /**
     * Gets database connection
     */
    public abstract Connection getConnection() throws DataAccessException;

    /**
     * Releases the connection.
     */
    public abstract void freeConnection(Connection conn) throws DataAccessException;

    /**
     * 释放资源
     *
     * @param conn
     * @param stmt
     * @param rs
     * @throws SQLException
     */
    public void release(Connection conn, Statement stmt, ResultSet rs) throws DataAccessException {
        this.release(rs);
        this.release(stmt);
        this.freeConnection(conn);
    }

    /**
     * 释放资源
     *
     * @param conn
     * @param stmt
     * @throws SQLException
     */
    public void release(Connection conn, Statement stmt) throws DataAccessException {
        this.release(stmt);
        this.freeConnection(conn);
    }

    /**
     * 释放游标
     *
     * @param stmt
     * @throws SQLException
     */
    public void release(Statement stmt) throws DataAccessException {

        try {
            if (stmt != null) {
                stmt.close();
            }
        } catch (SQLException e) {
            log.error("", e);
            throw new DataAccessException(e.getMessage());
        }
    }

    /**
     * 释放查询结果集
     *
     * @param rs
     * @throws SQLException
     */
    public void release(ResultSet rs) throws DataAccessException {
        try {
            if (rs != null) {
                rs.close();
            }
        } catch (SQLException e) {
            log.error("", e);
            throw new DataAccessException(e.getMessage());
        }
    }

}