"一般来说，Java 应用程序访问数据库的过程是：装载数据库驱动程序；通过 jdbc 建立数据库连接；访问数据库，执行 sql 语句；断开数据库连接。 [链接] public class DBConnection { private Connection con; //定义数据库连接类对象 p ...."

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AI开发者社区 • 0 回帖 • 3 浏览 • 4 个月前

Java数据库连接池实现原理

一般来说，Java 应用程序访问数据库的过程是：

装载数据库驱动程序；
通过 jdbc 建立数据库连接；
访问数据库，执行 sql 语句；
断开数据库连接。

public class DBConnection {
</span><span style="color: rgba(0, 0, 255, 1)">private</span> Connection con;         <span style="color: rgba(0, 128, 0, 1)">//</span><span style="color: rgba(0, 128, 0, 1)">定义数据库连接类对象</span>
<span style="color: rgba(0, 0, 255, 1)">private</span><span style="color: rgba(0, 0, 0, 1)"> PreparedStatement pstm;
</span><span style="color: rgba(0, 0, 255, 1)">private</span> String user="root";     <span style="color: rgba(0, 128, 0, 1)">//</span><span style="color: rgba(0, 128, 0, 1)">连接数据库用户名</span>
<span style="color: rgba(0, 0, 255, 1)">private</span> String password="123456";       <span style="color: rgba(0, 128, 0, 1)">//</span><span style="color: rgba(0, 128, 0, 1)">连接数据库密码</span>
<span style="color: rgba(0, 0, 255, 1)">private</span> String driverName="com.mysql.jdbc.Driver";  <span style="color: rgba(0, 128, 0, 1)">//</span><span style="color: rgba(0, 128, 0, 1)">数据库驱动</span>
<span style="color: rgba(0, 0, 255, 1)">private</span> String url="jdbc:mysql://localhost:3306/qingqingtuan"<span style="color: rgba(0, 0, 0, 1)">;

</span><span style="color: rgba(0, 128, 0, 1)">//</span><span style="color: rgba(0, 128, 0, 1)">连接数据库的URL,后面的是为了防止插入数据 库出现乱码，?useUnicode=true&amp;characterEncoding=UTF-8
</span><span style="color: rgba(0, 128, 0, 1)">//</span><span style="color: rgba(0, 128, 0, 1)">构造函数</span>
<span style="color: rgba(0, 0, 255, 1)">public</span><span style="color: rgba(0, 0, 0, 1)"> DBConnection() {

}

</span><span style="color: rgba(0, 128, 0, 1)">/**</span><span style="color: rgba(0, 128, 0, 1)">创建数据库连接</span><span style="color: rgba(0, 128, 0, 1)">*/</span>
<span style="color: rgba(0, 0, 255, 1)">public</span><span style="color: rgba(0, 0, 0, 1)"> Connection getConnection() {
    </span><span style="color: rgba(0, 0, 255, 1)">try</span><span style="color: rgba(0, 0, 0, 1)"> {
        Class.forName(</span>"com.mysql.jdbc.Driver"<span style="color: rgba(0, 0, 0, 1)">);
    } </span><span style="color: rgba(0, 0, 255, 1)">catch</span><span style="color: rgba(0, 0, 0, 1)">(ClassNotFoundException e) {
        System.out.println(</span>"加载数据库驱动失败！"<span style="color: rgba(0, 0, 0, 1)">);
        e.printStackTrace();
    }
    </span><span style="color: rgba(0, 0, 255, 1)">try</span><span style="color: rgba(0, 0, 0, 1)"> {
        con</span>=DriverManager.getConnection(url,user,password);     <span style="color: rgba(0, 128, 0, 1)">//</span><span style="color: rgba(0, 128, 0, 1)">获取数据库连接</span>
    } <span style="color: rgba(0, 0, 255, 1)">catch</span><span style="color: rgba(0, 0, 0, 1)"> (SQLException e) {
        System.out.println(</span>"创建数据库连接失败！"<span style="color: rgba(0, 0, 0, 1)">);
        con</span>=<span style="color: rgba(0, 0, 255, 1)">null</span><span style="color: rgba(0, 0, 0, 1)">;
        e.printStackTrace();
    }
    </span><span style="color: rgba(0, 0, 255, 1)">return</span> con;            <span style="color: rgba(0, 128, 0, 1)">//</span><span style="color: rgba(0, 128, 0, 1)">返回数据库连接对象</span>

    }
</span><span style="color: rgba(0, 0, 255, 1)">public</span> <span style="color: rgba(0, 0, 255, 1)">static</span> <span style="color: rgba(0, 0, 255, 1)">void</span><span style="color: rgba(0, 0, 0, 1)"> main(String[] args) {
    List</span>&lt;shop&gt; mShopList=<span style="color: rgba(0, 0, 255, 1)">new</span> ArrayList&lt;shop&gt;<span style="color: rgba(0, 0, 0, 1)">();
    Connection mConnection</span>=<span style="color: rgba(0, 0, 255, 1)">new</span><span style="color: rgba(0, 0, 0, 1)"> DBConnection().getConnection();
    </span><span style="color: rgba(0, 0, 255, 1)">if</span>(mConnection!=<span style="color: rgba(0, 0, 255, 1)">null</span><span style="color: rgba(0, 0, 0, 1)">) {
        </span><span style="color: rgba(0, 0, 255, 1)">try</span><span style="color: rgba(0, 0, 0, 1)"> {
            String sql</span>="select * from shop"<span style="color: rgba(0, 0, 0, 1)">;
            PreparedStatement pstm</span>=<span style="color: rgba(0, 0, 0, 1)">mConnection.prepareStatement(sql);
            ResultSet rs</span>=<span style="color: rgba(0, 0, 0, 1)">pstm.executeQuery();
            </span><span style="color: rgba(0, 0, 255, 1)">while</span><span style="color: rgba(0, 0, 0, 1)">(rs.next()) {
                ......</span><span style="color: rgba(0, 128, 0, 1)">//</span><span style="color: rgba(0, 128, 0, 1)">封装PoPj的操作</span>

                }
rs.close();
pstm.close();
} catch (SQLException e) {
e.printStackTrace();
}
finally {
try {
if(mConnection!=null) {
mConnection.close();
}
} catch (SQLException e) {
e.printStackTrace();
}
}
}
}
}

程序开发过程中，存在很多问题：

首先，每一次 web 请求都要建立一次数据库连接。建立连接是一个费时的活动，每次都得花费 0.05s～1s 的时间，而且系统还要分配内存资源。这个时间对于一次或几次数据库操作，或许感觉不出系统有多大的开销。可是对于现在的 web 应用，尤其是大型电子商务网站，同时有几百人甚至几千人在线是很正常的事。在这种情况下，频繁的进行数据库连接操作势必占用很多的系统资源，网站的响应速度必定下降，严重的甚至会造成服务器的崩溃。不是危言耸听，这就是制约某些电子商务网站发展的技术瓶颈问题。其次，对于每一次数据库连接，使用完后都得断开。否则，如果程序出现异常而未能关闭，将会导致数据库系统中的内存泄漏，最终将不得不重启数据库
通过上面的分析，我们可以看出来，“数据库连接”是一种稀缺的资源，为了保障网站的正常使用，应该对其进行妥善管理。其实我们查询完数据库后，如果不关闭连接，而是暂时存放起来，当别人使用时，把这个连接给他们使用。就避免了一次建立数据库连接和断开的操作时间消耗。数据库连接池的基本思想：就是为数据库连接建立一个“缓冲池”。预先在缓冲池中放入一定数量的连接，当需要建立数据库连接时，只需从“缓冲池”中取出一个，使用完毕之后再放回去。我们可以通过设定连接池最大连接数来防止系统无尽的与数据库连接

创建数据库连接池大概有 3 个步骤：

创建 ConnectionPool 实例，并初始化创建 10 个连接，保存在 Vector 中（线程安全）
实现 getConnection() 从连接库中获取一个可用的连接
returnConnection(conn) 提供将连接放回连接池中方法

//////////////////////////////// 数据库连接池类 ConnectionPool.java ////////////////////////////////////////

/*
 这个例子是根据 POSTGRESQL 数据库写的，
 请用的时候根据实际的数据库调整。
 调用方法如下：
 ①　ConnectionPool connPool
 = new ConnectionPool("com.microsoft.jdbc.sqlserver.SQLServerDriver"
 ,"jdbc:microsoft:sqlserver://localhost:1433;DatabaseName=MyDataForTest"
 ,"Username"
 ,"Password");
 ②　connPool .createPool();
 Connection conn = connPool .getConnection();
 connPool.returnConnection(conn);
 connPool.refreshConnections();
 connPool.closeConnectionPool();
 */
import java.sql.Connection;
import java.sql.DatabaseMetaData;
import java.sql.Driver;
import java.sql.DriverManager;
import java.sql.SQLException;
import java.sql.Statement;
import java.util.Enumeration;
import java.util.Vector;
public class ConnectionPool {
private String jdbcDriver = ""; // 数据库驱动
private String dbUrl = ""; // 数据 URL
private String dbUsername = ""; // 数据库用户名
private String dbPassword = ""; // 数据库用户密码
private String testTable = ""; // 测试连接是否可用的测试表名，默认没有测试表
<span style="color: rgba(0, 0, 255, 1)">private</span> <span style="color: rgba(0, 0, 255, 1)">int</span> initialConnections = 10; <span style="color: rgba(0, 128, 0, 1)">//</span><span style="color: rgba(0, 128, 0, 1)"> 连接池的初始大小</span>
<span style="color: rgba(0, 0, 255, 1)">private</span> <span style="color: rgba(0, 0, 255, 1)">int</span> incrementalConnections = 5;<span style="color: rgba(0, 128, 0, 1)">//</span><span style="color: rgba(0, 128, 0, 1)"> 连接池自动增加的大小</span>
<span style="color: rgba(0, 0, 255, 1)">private</span> <span style="color: rgba(0, 0, 255, 1)">int</span> maxConnections = 50; <span style="color: rgba(0, 128, 0, 1)">//</span><span style="color: rgba(0, 128, 0, 1)"> 连接池最大的大小</span>
<span style="color: rgba(0, 0, 255, 1)">private</span> Vector connections = <span style="color: rgba(0, 0, 255, 1)">null</span>; <span style="color: rgba(0, 128, 0, 1)">//</span><span style="color: rgba(0, 128, 0, 1)"> 存放连接池中数据库连接的向量 , 初始时为 null
</span><span style="color: rgba(0, 128, 0, 1)">//</span><span style="color: rgba(0, 128, 0, 1)"> 它中存放的对象为 PooledConnection 型</span>

<span style="color: rgba(0, 128, 0, 1)">/**</span><span style="color: rgba(0, 128, 0, 1)">
 * 构造函数
 *
 * </span><span style="color: rgba(128, 128, 128, 1)">@param</span><span style="color: rgba(0, 128, 0, 1)"> jdbcDriver
 *            String JDBC 驱动类串
 * </span><span style="color: rgba(128, 128, 128, 1)">@param</span><span style="color: rgba(0, 128, 0, 1)"> dbUrl
 *            String 数据库 URL
 * </span><span style="color: rgba(128, 128, 128, 1)">@param</span><span style="color: rgba(0, 128, 0, 1)"> dbUsername
 *            String 连接数据库用户名
 * </span><span style="color: rgba(128, 128, 128, 1)">@param</span><span style="color: rgba(0, 128, 0, 1)"> dbPassword
 *            String 连接数据库用户的密码
 *
 </span><span style="color: rgba(0, 128, 0, 1)">*/</span>
<span style="color: rgba(0, 0, 255, 1)">public</span><span style="color: rgba(0, 0, 0, 1)"> ConnectionPool(String jdbcDriver, String dbUrl, String dbUsername,
                      String dbPassword) {
    </span><span style="color: rgba(0, 0, 255, 1)">this</span>.jdbcDriver =<span style="color: rgba(0, 0, 0, 1)"> jdbcDriver;
    </span><span style="color: rgba(0, 0, 255, 1)">this</span>.dbUrl =<span style="color: rgba(0, 0, 0, 1)"> dbUrl;
    </span><span style="color: rgba(0, 0, 255, 1)">this</span>.dbUsername =<span style="color: rgba(0, 0, 0, 1)"> dbUsername;
    </span><span style="color: rgba(0, 0, 255, 1)">this</span>.dbPassword =<span style="color: rgba(0, 0, 0, 1)"> dbPassword;
}

</span><span style="color: rgba(0, 128, 0, 1)">/**</span><span style="color: rgba(0, 128, 0, 1)">
 * 返回连接池的初始大小
 *
 * </span><span style="color: rgba(128, 128, 128, 1)">@return</span><span style="color: rgba(0, 128, 0, 1)"> 初始连接池中可获得的连接数量
 </span><span style="color: rgba(0, 128, 0, 1)">*/</span>
<span style="color: rgba(0, 0, 255, 1)">public</span> <span style="color: rgba(0, 0, 255, 1)">int</span><span style="color: rgba(0, 0, 0, 1)"> getInitialConnections() {
    </span><span style="color: rgba(0, 0, 255, 1)">return</span> <span style="color: rgba(0, 0, 255, 1)">this</span><span style="color: rgba(0, 0, 0, 1)">.initialConnections;
}
</span><span style="color: rgba(0, 128, 0, 1)">/**</span><span style="color: rgba(0, 128, 0, 1)">
 * 设置连接池的初始大小
 *
 * </span><span style="color: rgba(128, 128, 128, 1)">@param</span><span style="color: rgba(0, 128, 0, 1)"> 用于设置初始连接池中连接的数量
 </span><span style="color: rgba(0, 128, 0, 1)">*/</span>
<span style="color: rgba(0, 0, 255, 1)">public</span> <span style="color: rgba(0, 0, 255, 1)">void</span> setInitialConnections(<span style="color: rgba(0, 0, 255, 1)">int</span><span style="color: rgba(0, 0, 0, 1)"> initialConnections) {
    </span><span style="color: rgba(0, 0, 255, 1)">this</span>.initialConnections =<span style="color: rgba(0, 0, 0, 1)"> initialConnections;
}
</span><span style="color: rgba(0, 128, 0, 1)">/**</span><span style="color: rgba(0, 128, 0, 1)">
 * 返回连接池自动增加的大小 、
 *
 * </span><span style="color: rgba(128, 128, 128, 1)">@return</span><span style="color: rgba(0, 128, 0, 1)"> 连接池自动增加的大小
 </span><span style="color: rgba(0, 128, 0, 1)">*/</span>
<span style="color: rgba(0, 0, 255, 1)">public</span> <span style="color: rgba(0, 0, 255, 1)">int</span><span style="color: rgba(0, 0, 0, 1)"> getIncrementalConnections() {
    </span><span style="color: rgba(0, 0, 255, 1)">return</span> <span style="color: rgba(0, 0, 255, 1)">this</span><span style="color: rgba(0, 0, 0, 1)">.incrementalConnections;
}
</span><span style="color: rgba(0, 128, 0, 1)">/**</span><span style="color: rgba(0, 128, 0, 1)">
 * 设置连接池自动增加的大小
 *
 * </span><span style="color: rgba(128, 128, 128, 1)">@param</span><span style="color: rgba(0, 128, 0, 1)"> 连接池自动增加的大小
 </span><span style="color: rgba(0, 128, 0, 1)">*/</span>

<span style="color: rgba(0, 0, 255, 1)">public</span> <span style="color: rgba(0, 0, 255, 1)">void</span> setIncrementalConnections(<span style="color: rgba(0, 0, 255, 1)">int</span><span style="color: rgba(0, 0, 0, 1)"> incrementalConnections) {
    </span><span style="color: rgba(0, 0, 255, 1)">this</span>.incrementalConnections =<span style="color: rgba(0, 0, 0, 1)"> incrementalConnections;
}
</span><span style="color: rgba(0, 128, 0, 1)">/**</span><span style="color: rgba(0, 128, 0, 1)">
 * 返回连接池中最大的可用连接数量
 *
 * </span><span style="color: rgba(128, 128, 128, 1)">@return</span><span style="color: rgba(0, 128, 0, 1)"> 连接池中最大的可用连接数量
 </span><span style="color: rgba(0, 128, 0, 1)">*/</span>
<span style="color: rgba(0, 0, 255, 1)">public</span> <span style="color: rgba(0, 0, 255, 1)">int</span><span style="color: rgba(0, 0, 0, 1)"> getMaxConnections() {
    </span><span style="color: rgba(0, 0, 255, 1)">return</span> <span style="color: rgba(0, 0, 255, 1)">this</span><span style="color: rgba(0, 0, 0, 1)">.maxConnections;
}
</span><span style="color: rgba(0, 128, 0, 1)">/**</span><span style="color: rgba(0, 128, 0, 1)">
 * 设置连接池中最大可用的连接数量
 *
 * </span><span style="color: rgba(128, 128, 128, 1)">@param</span><span style="color: rgba(0, 128, 0, 1)"> 设置连接池中最大可用的连接数量值
 </span><span style="color: rgba(0, 128, 0, 1)">*/</span>
<span style="color: rgba(0, 0, 255, 1)">public</span> <span style="color: rgba(0, 0, 255, 1)">void</span> setMaxConnections(<span style="color: rgba(0, 0, 255, 1)">int</span><span style="color: rgba(0, 0, 0, 1)"> maxConnections) {
    </span><span style="color: rgba(0, 0, 255, 1)">this</span>.maxConnections =<span style="color: rgba(0, 0, 0, 1)"> maxConnections;
}

</span><span style="color: rgba(0, 128, 0, 1)">/**</span><span style="color: rgba(0, 128, 0, 1)">
 * 获取测试数据库表的名字
 *
 * </span><span style="color: rgba(128, 128, 128, 1)">@return</span><span style="color: rgba(0, 128, 0, 1)"> 测试数据库表的名字
 </span><span style="color: rgba(0, 128, 0, 1)">*/</span>

<span style="color: rgba(0, 0, 255, 1)">public</span><span style="color: rgba(0, 0, 0, 1)"> String getTestTable() {
    </span><span style="color: rgba(0, 0, 255, 1)">return</span> <span style="color: rgba(0, 0, 255, 1)">this</span><span style="color: rgba(0, 0, 0, 1)">.testTable;
}

</span><span style="color: rgba(0, 128, 0, 1)">/**</span><span style="color: rgba(0, 128, 0, 1)">
 * 设置测试表的名字
 *
 * </span><span style="color: rgba(128, 128, 128, 1)">@param</span><span style="color: rgba(0, 128, 0, 1)"> testTable
 *            String 测试表的名字
 </span><span style="color: rgba(0, 128, 0, 1)">*/</span>

<span style="color: rgba(0, 0, 255, 1)">public</span> <span style="color: rgba(0, 0, 255, 1)">void</span><span style="color: rgba(0, 0, 0, 1)"> setTestTable(String testTable) {
    </span><span style="color: rgba(0, 0, 255, 1)">this</span>.testTable =<span style="color: rgba(0, 0, 0, 1)"> testTable;
}

</span><span style="color: rgba(0, 128, 0, 1)">/**</span><span style="color: rgba(0, 128, 0, 1)">
 *
 * 创建一个数据库连接池，连接池中的可用连接的数量采用类成员 initialConnections 中设置的值
 </span><span style="color: rgba(0, 128, 0, 1)">*/</span>

<span style="color: rgba(0, 0, 255, 1)">public</span> <span style="color: rgba(0, 0, 255, 1)">synchronized</span> <span style="color: rgba(0, 0, 255, 1)">void</span> createPool() <span style="color: rgba(0, 0, 255, 1)">throws</span><span style="color: rgba(0, 0, 0, 1)"> Exception {
    </span><span style="color: rgba(0, 128, 0, 1)">//</span><span style="color: rgba(0, 128, 0, 1)"> 确保连接池没有创建
    </span><span style="color: rgba(0, 128, 0, 1)">//</span><span style="color: rgba(0, 128, 0, 1)"> 如果连接池己经创建了，保存连接的向量 connections 不会为空</span>
    <span style="color: rgba(0, 0, 255, 1)">if</span> (connections != <span style="color: rgba(0, 0, 255, 1)">null</span><span style="color: rgba(0, 0, 0, 1)">) {
        </span><span style="color: rgba(0, 0, 255, 1)">return</span>; <span style="color: rgba(0, 128, 0, 1)">//</span><span style="color: rgba(0, 128, 0, 1)"> 如果己经创建，则返回</span>

        }
// 实例化 JDBC Driver 中指定的驱动类实例
Driver driver = (Driver) (Class.forName(this.jdbcDriver).newInstance());
DriverManager.registerDriver(driver); // 注册 JDBC 驱动程序
// 创建保存连接的向量 , 初始时有 0 个元素
connections = new Vector();
// 根据 initialConnections 中设置的值，创建连接。
createConnections(this.initialConnections);
// System.out.println("数据库连接池创建成功！");
    }
</span><span style="color: rgba(0, 128, 0, 1)">/**</span><span style="color: rgba(0, 128, 0, 1)">
 * 创建由 numConnections 指定数目的数据库连接 , 并把这些连接 放入 connections 向量中
 *
 * </span><span style="color: rgba(128, 128, 128, 1)">@param</span><span style="color: rgba(0, 128, 0, 1)"> numConnections
 *            要创建的数据库连接的数目
 </span><span style="color: rgba(0, 128, 0, 1)">*/</span>

<span style="color: rgba(0, 0, 255, 1)">private</span> <span style="color: rgba(0, 0, 255, 1)">void</span> createConnections(<span style="color: rgba(0, 0, 255, 1)">int</span> numConnections) <span style="color: rgba(0, 0, 255, 1)">throws</span><span style="color: rgba(0, 0, 0, 1)"> SQLException {
    </span><span style="color: rgba(0, 128, 0, 1)">//</span><span style="color: rgba(0, 128, 0, 1)"> 循环创建指定数目的数据库连接</span>
    <span style="color: rgba(0, 0, 255, 1)">for</span> (<span style="color: rgba(0, 0, 255, 1)">int</span> x = 0; x &lt; numConnections; x++<span style="color: rgba(0, 0, 0, 1)">) {
        </span><span style="color: rgba(0, 128, 0, 1)">//</span><span style="color: rgba(0, 128, 0, 1)"> 是否连接池中的数据库连接的数量己经达到最大？最大值由类成员 maxConnections
        </span><span style="color: rgba(0, 128, 0, 1)">//</span><span style="color: rgba(0, 128, 0, 1)"> 指出，如果 maxConnections 为 0 或负数，表示连接数量没有限制。
        </span><span style="color: rgba(0, 128, 0, 1)">//</span><span style="color: rgba(0, 128, 0, 1)"> 如果连接数己经达到最大，即退出。</span>
        <span style="color: rgba(0, 0, 255, 1)">if</span> (<span style="color: rgba(0, 0, 255, 1)">this</span>.maxConnections &gt; 0
        &amp;&amp; <span style="color: rgba(0, 0, 255, 1)">this</span>.connections.size() &gt;= <span style="color: rgba(0, 0, 255, 1)">this</span><span style="color: rgba(0, 0, 0, 1)">.maxConnections) {
            </span><span style="color: rgba(0, 0, 255, 1)">break</span><span style="color: rgba(0, 0, 0, 1)">;
        }
        </span><span style="color: rgba(0, 128, 0, 1)">//</span><span style="color: rgba(0, 128, 0, 1)"> add a new PooledConnection object to connections vector
        </span><span style="color: rgba(0, 128, 0, 1)">//</span><span style="color: rgba(0, 128, 0, 1)"> 增加一个连接到连接池中（向量 connections 中）</span>
        <span style="color: rgba(0, 0, 255, 1)">try</span><span style="color: rgba(0, 0, 0, 1)"> {
            connections.addElement(</span><span style="color: rgba(0, 0, 255, 1)">new</span><span style="color: rgba(0, 0, 0, 1)"> PooledConnection(newConnection()));
        } </span><span style="color: rgba(0, 0, 255, 1)">catch</span><span style="color: rgba(0, 0, 0, 1)"> (SQLException e) {
            System.out.println(</span>" 创建数据库连接失败！ " +<span style="color: rgba(0, 0, 0, 1)"> e.getMessage());
            </span><span style="color: rgba(0, 0, 255, 1)">throw</span> <span style="color: rgba(0, 0, 255, 1)">new</span><span style="color: rgba(0, 0, 0, 1)"> SQLException();
        }
        </span><span style="color: rgba(0, 128, 0, 1)">//</span><span style="color: rgba(0, 128, 0, 1)"> System.out.println(" 数据库连接己创建 ......");</span>

        }
}
/**
* 创建一个新的数据库连接并返回它
*
* @return 返回一个新创建的数据库连接
*/
private Connection newConnection() throws SQLException {
// 创建一个数据库连接
Connection conn = DriverManager.getConnection(dbUrl, dbUsername,
dbPassword);
// 如果这是第一次创建数据库连接，即检查数据库，获得此数据库允许支持的
// 最大客户连接数目
// connections.size()==0 表示目前没有连接己被创建
if (connections.size() == 0) {
DatabaseMetaData metaData = conn.getMetaData();
int driverMaxConnections = metaData.getMaxConnections();
// 数据库返回的 driverMaxConnections 若为 0 ，表示此数据库没有最大
// 连接限制，或数据库的最大连接限制不知道
// driverMaxConnections 为返回的一个整数，表示此数据库允许客户连接的数目
// 如果连接池中设置的最大连接数量大于数据库允许的连接数目 , 则置连接池的最大
// 连接数目为数据库允许的最大数目
if (driverMaxConnections > 0
&& this.maxConnections > driverMaxConnections) {
this.maxConnections = driverMaxConnections;
}
}
return conn; // 返回创建的新的数据库连接
    }
</span><span style="color: rgba(0, 128, 0, 1)">/**</span><span style="color: rgba(0, 128, 0, 1)">
 * 通过调用 getFreeConnection() 函数返回一个可用的数据库连接 , 如果当前没有可用的数据库连接，并且更多的数据库连接不能创
 * 建（如连接池大小的限制），此函数等待一会再尝试获取。
 *
 * </span><span style="color: rgba(128, 128, 128, 1)">@return</span><span style="color: rgba(0, 128, 0, 1)"> 返回一个可用的数据库连接对象
 </span><span style="color: rgba(0, 128, 0, 1)">*/</span>

<span style="color: rgba(0, 0, 255, 1)">public</span> <span style="color: rgba(0, 0, 255, 1)">synchronized</span> Connection getConnection() <span style="color: rgba(0, 0, 255, 1)">throws</span><span style="color: rgba(0, 0, 0, 1)"> SQLException {
    </span><span style="color: rgba(0, 128, 0, 1)">//</span><span style="color: rgba(0, 128, 0, 1)"> 确保连接池己被创建</span>
    <span style="color: rgba(0, 0, 255, 1)">if</span> (connections == <span style="color: rgba(0, 0, 255, 1)">null</span><span style="color: rgba(0, 0, 0, 1)">) {
        </span><span style="color: rgba(0, 0, 255, 1)">return</span> <span style="color: rgba(0, 0, 255, 1)">null</span>; <span style="color: rgba(0, 128, 0, 1)">//</span><span style="color: rgba(0, 128, 0, 1)"> 连接池还没创建，则返回 null</span>

        }
Connection conn = getFreeConnection(); // 获得一个可用的数据库连接
// 如果目前没有可以使用的连接，即所有的连接都在使用中
while (conn == null) {
// 等一会再试
// System.out.println("Wait");
wait(250);
conn = getFreeConnection(); // 重新再试，直到获得可用的连接，如果
// getFreeConnection() 返回的为 null
// 则表明创建一批连接后也不可获得可用连接
        }
return conn;// 返回获得的可用的连接
    }
</span><span style="color: rgba(0, 128, 0, 1)">/**</span><span style="color: rgba(0, 128, 0, 1)">
 * 本函数从连接池向量 connections 中返回一个可用的的数据库连接，如果 当前没有可用的数据库连接，本函数则根据
 * incrementalConnections 设置 的值创建几个数据库连接，并放入连接池中。 如果创建后，所有的连接仍都在使用中，则返回 null
 *
 * </span><span style="color: rgba(128, 128, 128, 1)">@return</span><span style="color: rgba(0, 128, 0, 1)"> 返回一个可用的数据库连接
 </span><span style="color: rgba(0, 128, 0, 1)">*/</span>
<span style="color: rgba(0, 0, 255, 1)">private</span> Connection getFreeConnection() <span style="color: rgba(0, 0, 255, 1)">throws</span><span style="color: rgba(0, 0, 0, 1)"> SQLException {
    </span><span style="color: rgba(0, 128, 0, 1)">//</span><span style="color: rgba(0, 128, 0, 1)"> 从连接池中获得一个可用的数据库连接</span>
    Connection conn =<span style="color: rgba(0, 0, 0, 1)"> findFreeConnection();
    </span><span style="color: rgba(0, 0, 255, 1)">if</span> (conn == <span style="color: rgba(0, 0, 255, 1)">null</span><span style="color: rgba(0, 0, 0, 1)">) {
        </span><span style="color: rgba(0, 128, 0, 1)">//</span><span style="color: rgba(0, 128, 0, 1)"> 如果目前连接池中没有可用的连接
        </span><span style="color: rgba(0, 128, 0, 1)">//</span><span style="color: rgba(0, 128, 0, 1)"> 创建一些连接</span>

            createConnections(incrementalConnections);
// 重新从池中查找是否有可用连接
conn = findFreeConnection();
if (conn == null) {
// 如果创建连接后仍获得不到可用的连接，则返回 null
return null;
}
}
return conn;
}
</span><span style="color: rgba(0, 128, 0, 1)">/**</span><span style="color: rgba(0, 128, 0, 1)">
 * 查找连接池中所有的连接，查找一个可用的数据库连接， 如果没有可用的连接，返回 null
 *
 * </span><span style="color: rgba(128, 128, 128, 1)">@return</span><span style="color: rgba(0, 128, 0, 1)"> 返回一个可用的数据库连接
 </span><span style="color: rgba(0, 128, 0, 1)">*/</span>

<span style="color: rgba(0, 0, 255, 1)">private</span> Connection findFreeConnection() <span style="color: rgba(0, 0, 255, 1)">throws</span><span style="color: rgba(0, 0, 0, 1)"> SQLException {
    Connection conn </span>= <span style="color: rgba(0, 0, 255, 1)">null</span><span style="color: rgba(0, 0, 0, 1)">;
    PooledConnection pConn </span>= <span style="color: rgba(0, 0, 255, 1)">null</span><span style="color: rgba(0, 0, 0, 1)">;
    </span><span style="color: rgba(0, 128, 0, 1)">//</span><span style="color: rgba(0, 128, 0, 1)"> 获得连接池向量中所有的对象</span>
    Enumeration enumerate =<span style="color: rgba(0, 0, 0, 1)"> connections.elements();
    </span><span style="color: rgba(0, 128, 0, 1)">//</span><span style="color: rgba(0, 128, 0, 1)"> 遍历所有的对象，看是否有可用的连接</span>
    <span style="color: rgba(0, 0, 255, 1)">while</span><span style="color: rgba(0, 0, 0, 1)"> (enumerate.hasMoreElements()) {
        pConn </span>=<span style="color: rgba(0, 0, 0, 1)"> (PooledConnection) enumerate.nextElement();
        </span><span style="color: rgba(0, 0, 255, 1)">if</span> (!<span style="color: rgba(0, 0, 0, 1)">pConn.isBusy()) {
            </span><span style="color: rgba(0, 128, 0, 1)">//</span><span style="color: rgba(0, 128, 0, 1)"> 如果此对象不忙，则获得它的数据库连接并把它设为忙</span>
            conn =<span style="color: rgba(0, 0, 0, 1)"> pConn.getConnection();
            pConn.setBusy(</span><span style="color: rgba(0, 0, 255, 1)">true</span><span style="color: rgba(0, 0, 0, 1)">);
            </span><span style="color: rgba(0, 128, 0, 1)">//</span><span style="color: rgba(0, 128, 0, 1)"> 测试此连接是否可用</span>
            <span style="color: rgba(0, 0, 255, 1)">if</span> (!<span style="color: rgba(0, 0, 0, 1)">testConnection(conn)) {
                </span><span style="color: rgba(0, 128, 0, 1)">//</span><span style="color: rgba(0, 128, 0, 1)"> 如果此连接不可再用了，则创建一个新的连接，
                </span><span style="color: rgba(0, 128, 0, 1)">//</span><span style="color: rgba(0, 128, 0, 1)"> 并替换此不可用的连接对象，如果创建失败，返回 null</span>
                <span style="color: rgba(0, 0, 255, 1)">try</span><span style="color: rgba(0, 0, 0, 1)"> {
                    conn </span>=<span style="color: rgba(0, 0, 0, 1)"> newConnection();
                } </span><span style="color: rgba(0, 0, 255, 1)">catch</span><span style="color: rgba(0, 0, 0, 1)"> (SQLException e) {
                    System.out.println(</span>" 创建数据库连接失败！ " +<span style="color: rgba(0, 0, 0, 1)"> e.getMessage());
                    </span><span style="color: rgba(0, 0, 255, 1)">return</span> <span style="color: rgba(0, 0, 255, 1)">null</span><span style="color: rgba(0, 0, 0, 1)">;
                }
                pConn.setConnection(conn);
            }
            </span><span style="color: rgba(0, 0, 255, 1)">break</span>; <span style="color: rgba(0, 128, 0, 1)">//</span><span style="color: rgba(0, 128, 0, 1)"> 己经找到一个可用的连接，退出</span>

            }
}
return conn;// 返回找到到的可用连接
    }
</span><span style="color: rgba(0, 128, 0, 1)">/**</span><span style="color: rgba(0, 128, 0, 1)">
 * 测试一个连接是否可用，如果不可用，关掉它并返回 false 否则可用返回 true
 *
 * </span><span style="color: rgba(128, 128, 128, 1)">@param</span><span style="color: rgba(0, 128, 0, 1)"> conn
 *            需要测试的数据库连接
 * </span><span style="color: rgba(128, 128, 128, 1)">@return</span><span style="color: rgba(0, 128, 0, 1)"> 返回 true 表示此连接可用， false 表示不可用
 </span><span style="color: rgba(0, 128, 0, 1)">*/</span>

<span style="color: rgba(0, 0, 255, 1)">private</span> <span style="color: rgba(0, 0, 255, 1)">boolean</span><span style="color: rgba(0, 0, 0, 1)"> testConnection(Connection conn) {
    </span><span style="color: rgba(0, 0, 255, 1)">try</span><span style="color: rgba(0, 0, 0, 1)"> {
        </span><span style="color: rgba(0, 128, 0, 1)">//</span><span style="color: rgba(0, 128, 0, 1)"> 判断测试表是否存在</span>
        <span style="color: rgba(0, 0, 255, 1)">if</span> (testTable.equals(""<span style="color: rgba(0, 0, 0, 1)">)) {
            </span><span style="color: rgba(0, 128, 0, 1)">//</span><span style="color: rgba(0, 128, 0, 1)"> 如果测试表为空，试着使用此连接的 setAutoCommit() 方法
            </span><span style="color: rgba(0, 128, 0, 1)">//</span><span style="color: rgba(0, 128, 0, 1)"> 来判断连接否可用（此方法只在部分数据库可用，如果不可用 ,
            </span><span style="color: rgba(0, 128, 0, 1)">//</span><span style="color: rgba(0, 128, 0, 1)"> 抛出异常）。注意：使用测试表的方法更可靠</span>
            conn.setAutoCommit(<span style="color: rgba(0, 0, 255, 1)">true</span><span style="color: rgba(0, 0, 0, 1)">);
        } </span><span style="color: rgba(0, 0, 255, 1)">else</span> {<span style="color: rgba(0, 128, 0, 1)">//</span><span style="color: rgba(0, 128, 0, 1)"> 有测试表的时候使用测试表测试
            </span><span style="color: rgba(0, 128, 0, 1)">//</span><span style="color: rgba(0, 128, 0, 1)"> check if this connection is valid</span>
            Statement stmt =<span style="color: rgba(0, 0, 0, 1)"> conn.createStatement();
            stmt.execute(</span>"select count(*) from " +<span style="color: rgba(0, 0, 0, 1)"> testTable);
        }
    } </span><span style="color: rgba(0, 0, 255, 1)">catch</span><span style="color: rgba(0, 0, 0, 1)"> (SQLException e) {
        </span><span style="color: rgba(0, 128, 0, 1)">//</span><span style="color: rgba(0, 128, 0, 1)"> 上面抛出异常，此连接己不可用，关闭它，并返回 false;</span>

            closeConnection(conn);
return false;
}
// 连接可用，返回 true
return true;
}
</span><span style="color: rgba(0, 128, 0, 1)">/**</span><span style="color: rgba(0, 128, 0, 1)">
 * 此函数返回一个数据库连接到连接池中，并把此连接置为空闲。 所有使用连接池获得的数据库连接均应在不使用此连接时返回它。
 *
 * </span><span style="color: rgba(128, 128, 128, 1)">@param</span><span style="color: rgba(0, 128, 0, 1)"> 需返回到连接池中的连接对象
 </span><span style="color: rgba(0, 128, 0, 1)">*/</span>

<span style="color: rgba(0, 0, 255, 1)">public</span> <span style="color: rgba(0, 0, 255, 1)">void</span><span style="color: rgba(0, 0, 0, 1)"> returnConnection(Connection conn) {
    </span><span style="color: rgba(0, 128, 0, 1)">//</span><span style="color: rgba(0, 128, 0, 1)"> 确保连接池存在，如果连接没有创建（不存在），直接返回</span>
    <span style="color: rgba(0, 0, 255, 1)">if</span> (connections == <span style="color: rgba(0, 0, 255, 1)">null</span><span style="color: rgba(0, 0, 0, 1)">) {
        System.out.println(</span>" 连接池不存在，无法返回此连接到连接池中 !"<span style="color: rgba(0, 0, 0, 1)">);
        </span><span style="color: rgba(0, 0, 255, 1)">return</span><span style="color: rgba(0, 0, 0, 1)">;
    }
    PooledConnection pConn </span>= <span style="color: rgba(0, 0, 255, 1)">null</span><span style="color: rgba(0, 0, 0, 1)">;
    Enumeration enumerate </span>=<span style="color: rgba(0, 0, 0, 1)"> connections.elements();
    </span><span style="color: rgba(0, 128, 0, 1)">//</span><span style="color: rgba(0, 128, 0, 1)"> 遍历连接池中的所有连接，找到这个要返回的连接对象</span>
    <span style="color: rgba(0, 0, 255, 1)">while</span><span style="color: rgba(0, 0, 0, 1)"> (enumerate.hasMoreElements()) {
        pConn </span>=<span style="color: rgba(0, 0, 0, 1)"> (PooledConnection) enumerate.nextElement();
        </span><span style="color: rgba(0, 128, 0, 1)">//</span><span style="color: rgba(0, 128, 0, 1)"> 先找到连接池中的要返回的连接对象</span>
        <span style="color: rgba(0, 0, 255, 1)">if</span> (conn ==<span style="color: rgba(0, 0, 0, 1)"> pConn.getConnection()) {
            </span><span style="color: rgba(0, 128, 0, 1)">//</span><span style="color: rgba(0, 128, 0, 1)"> 找到了 , 设置此连接为空闲状态</span>
            pConn.setBusy(<span style="color: rgba(0, 0, 255, 1)">false</span><span style="color: rgba(0, 0, 0, 1)">);
            </span><span style="color: rgba(0, 0, 255, 1)">break</span><span style="color: rgba(0, 0, 0, 1)">;
        }
    }
}

</span><span style="color: rgba(0, 128, 0, 1)">/**</span><span style="color: rgba(0, 128, 0, 1)">
 * 刷新连接池中所有的连接对象
 *
 </span><span style="color: rgba(0, 128, 0, 1)">*/</span>

<span style="color: rgba(0, 0, 255, 1)">public</span> <span style="color: rgba(0, 0, 255, 1)">synchronized</span> <span style="color: rgba(0, 0, 255, 1)">void</span> refreshConnections() <span style="color: rgba(0, 0, 255, 1)">throws</span><span style="color: rgba(0, 0, 0, 1)"> SQLException {
    </span><span style="color: rgba(0, 128, 0, 1)">//</span><span style="color: rgba(0, 128, 0, 1)"> 确保连接池己创新存在</span>
    <span style="color: rgba(0, 0, 255, 1)">if</span> (connections == <span style="color: rgba(0, 0, 255, 1)">null</span><span style="color: rgba(0, 0, 0, 1)">) {
        System.out.println(</span>" 连接池不存在，无法刷新 !"<span style="color: rgba(0, 0, 0, 1)">);
        </span><span style="color: rgba(0, 0, 255, 1)">return</span><span style="color: rgba(0, 0, 0, 1)">;
    }
    PooledConnection pConn </span>= <span style="color: rgba(0, 0, 255, 1)">null</span><span style="color: rgba(0, 0, 0, 1)">;
    Enumeration enumerate </span>=<span style="color: rgba(0, 0, 0, 1)"> connections.elements();
    </span><span style="color: rgba(0, 0, 255, 1)">while</span><span style="color: rgba(0, 0, 0, 1)"> (enumerate.hasMoreElements()) {
        </span><span style="color: rgba(0, 128, 0, 1)">//</span><span style="color: rgba(0, 128, 0, 1)"> 获得一个连接对象</span>
        pConn =<span style="color: rgba(0, 0, 0, 1)"> (PooledConnection) enumerate.nextElement();
        </span><span style="color: rgba(0, 128, 0, 1)">//</span><span style="color: rgba(0, 128, 0, 1)"> 如果对象忙则等 5 秒 ,5 秒后直接刷新</span>
        <span style="color: rgba(0, 0, 255, 1)">if</span><span style="color: rgba(0, 0, 0, 1)"> (pConn.isBusy()) {
            wait(</span>5000); <span style="color: rgba(0, 128, 0, 1)">//</span><span style="color: rgba(0, 128, 0, 1)"> 等 5 秒</span>

            }
// 关闭此连接，用一个新的连接代替它。
            closeConnection(pConn.getConnection());
pConn.setConnection(newConnection());
pConn.setBusy(false);
}
}
</span><span style="color: rgba(0, 128, 0, 1)">/**</span><span style="color: rgba(0, 128, 0, 1)">
 * 关闭连接池中所有的连接，并清空连接池。
 </span><span style="color: rgba(0, 128, 0, 1)">*/</span>

<span style="color: rgba(0, 0, 255, 1)">public</span> <span style="color: rgba(0, 0, 255, 1)">synchronized</span> <span style="color: rgba(0, 0, 255, 1)">void</span> closeConnectionPool() <span style="color: rgba(0, 0, 255, 1)">throws</span><span style="color: rgba(0, 0, 0, 1)"> SQLException {
    </span><span style="color: rgba(0, 128, 0, 1)">//</span><span style="color: rgba(0, 128, 0, 1)"> 确保连接池存在，如果不存在，返回</span>
    <span style="color: rgba(0, 0, 255, 1)">if</span> (connections == <span style="color: rgba(0, 0, 255, 1)">null</span><span style="color: rgba(0, 0, 0, 1)">) {
        System.out.println(</span>" 连接池不存在，无法关闭 !"<span style="color: rgba(0, 0, 0, 1)">);
        </span><span style="color: rgba(0, 0, 255, 1)">return</span><span style="color: rgba(0, 0, 0, 1)">;
    }
    PooledConnection pConn </span>= <span style="color: rgba(0, 0, 255, 1)">null</span><span style="color: rgba(0, 0, 0, 1)">;
    Enumeration enumerate </span>=<span style="color: rgba(0, 0, 0, 1)"> connections.elements();
    </span><span style="color: rgba(0, 0, 255, 1)">while</span><span style="color: rgba(0, 0, 0, 1)"> (enumerate.hasMoreElements()) {
        pConn </span>=<span style="color: rgba(0, 0, 0, 1)"> (PooledConnection) enumerate.nextElement();
        </span><span style="color: rgba(0, 128, 0, 1)">//</span><span style="color: rgba(0, 128, 0, 1)"> 如果忙，等 5 秒</span>
        <span style="color: rgba(0, 0, 255, 1)">if</span><span style="color: rgba(0, 0, 0, 1)"> (pConn.isBusy()) {
            wait(</span>5000); <span style="color: rgba(0, 128, 0, 1)">//</span><span style="color: rgba(0, 128, 0, 1)"> 等 5 秒</span>

            }
// 5 秒后直接关闭它
            closeConnection(pConn.getConnection());
// 从连接池向量中删除它
            connections.removeElement(pConn);
}
// 置连接池为空
connections = null;
}
</span><span style="color: rgba(0, 128, 0, 1)">/**</span><span style="color: rgba(0, 128, 0, 1)">
 * 关闭一个数据库连接
 *
 * </span><span style="color: rgba(128, 128, 128, 1)">@param</span><span style="color: rgba(0, 128, 0, 1)"> 需要关闭的数据库连接
 </span><span style="color: rgba(0, 128, 0, 1)">*/</span>

<span style="color: rgba(0, 0, 255, 1)">private</span> <span style="color: rgba(0, 0, 255, 1)">void</span><span style="color: rgba(0, 0, 0, 1)"> closeConnection(Connection conn) {
    </span><span style="color: rgba(0, 0, 255, 1)">try</span><span style="color: rgba(0, 0, 0, 1)"> {
        conn.close();
    } </span><span style="color: rgba(0, 0, 255, 1)">catch</span><span style="color: rgba(0, 0, 0, 1)"> (SQLException e) {
        System.out.println(</span>" 关闭数据库连接出错： " +<span style="color: rgba(0, 0, 0, 1)"> e.getMessage());
    }
}
</span><span style="color: rgba(0, 128, 0, 1)">/**</span><span style="color: rgba(0, 128, 0, 1)">
 * 使程序等待给定的毫秒数
 *
 * </span><span style="color: rgba(128, 128, 128, 1)">@param</span><span style="color: rgba(0, 128, 0, 1)"> 给定的毫秒数
 </span><span style="color: rgba(0, 128, 0, 1)">*/</span>

<span style="color: rgba(0, 0, 255, 1)">private</span> <span style="color: rgba(0, 0, 255, 1)">void</span> wait(<span style="color: rgba(0, 0, 255, 1)">int</span><span style="color: rgba(0, 0, 0, 1)"> mSeconds) {
    </span><span style="color: rgba(0, 0, 255, 1)">try</span><span style="color: rgba(0, 0, 0, 1)"> {
        Thread.sleep(mSeconds);
    } </span><span style="color: rgba(0, 0, 255, 1)">catch</span><span style="color: rgba(0, 0, 0, 1)"> (InterruptedException e) {
    }
}
</span><span style="color: rgba(0, 128, 0, 1)">/**</span><span style="color: rgba(0, 128, 0, 1)">
 *
 * 内部使用的用于保存连接池中连接对象的类 此类中有两个成员，一个是数据库的连接，另一个是指示此连接是否 正在使用的标志。
 </span><span style="color: rgba(0, 128, 0, 1)">*/</span>

<span style="color: rgba(0, 0, 255, 1)">class</span><span style="color: rgba(0, 0, 0, 1)"> PooledConnection {
    Connection connection </span>= <span style="color: rgba(0, 0, 255, 1)">null</span>;<span style="color: rgba(0, 128, 0, 1)">//</span><span style="color: rgba(0, 128, 0, 1)"> 数据库连接</span>
    <span style="color: rgba(0, 0, 255, 1)">boolean</span> busy = <span style="color: rgba(0, 0, 255, 1)">false</span>; <span style="color: rgba(0, 128, 0, 1)">//</span><span style="color: rgba(0, 128, 0, 1)"> 此连接是否正在使用的标志，默认没有正在使用

    </span><span style="color: rgba(0, 128, 0, 1)">//</span><span style="color: rgba(0, 128, 0, 1)"> 构造函数，根据一个 Connection 构告一个 PooledConnection 对象</span>
    <span style="color: rgba(0, 0, 255, 1)">public</span><span style="color: rgba(0, 0, 0, 1)"> PooledConnection(Connection connection) {
        </span><span style="color: rgba(0, 0, 255, 1)">this</span>.connection =<span style="color: rgba(0, 0, 0, 1)"> connection;
    }

    </span><span style="color: rgba(0, 128, 0, 1)">//</span><span style="color: rgba(0, 128, 0, 1)"> 返回此对象中的连接</span>
    <span style="color: rgba(0, 0, 255, 1)">public</span><span style="color: rgba(0, 0, 0, 1)"> Connection getConnection() {
        </span><span style="color: rgba(0, 0, 255, 1)">return</span><span style="color: rgba(0, 0, 0, 1)"> connection;
    }

    </span><span style="color: rgba(0, 128, 0, 1)">//</span><span style="color: rgba(0, 128, 0, 1)"> 设置此对象的，连接</span>
    <span style="color: rgba(0, 0, 255, 1)">public</span> <span style="color: rgba(0, 0, 255, 1)">void</span><span style="color: rgba(0, 0, 0, 1)"> setConnection(Connection connection) {
        </span><span style="color: rgba(0, 0, 255, 1)">this</span>.connection =<span style="color: rgba(0, 0, 0, 1)"> connection;
    }

    </span><span style="color: rgba(0, 128, 0, 1)">//</span><span style="color: rgba(0, 128, 0, 1)"> 获得对象连接是否忙</span>
    <span style="color: rgba(0, 0, 255, 1)">public</span> <span style="color: rgba(0, 0, 255, 1)">boolean</span><span style="color: rgba(0, 0, 0, 1)"> isBusy() {
        </span><span style="color: rgba(0, 0, 255, 1)">return</span><span style="color: rgba(0, 0, 0, 1)"> busy;
    }

    </span><span style="color: rgba(0, 128, 0, 1)">//</span><span style="color: rgba(0, 128, 0, 1)"> 设置对象的连接正在忙</span>
    <span style="color: rgba(0, 0, 255, 1)">public</span> <span style="color: rgba(0, 0, 255, 1)">void</span> setBusy(<span style="color: rgba(0, 0, 255, 1)">boolean</span><span style="color: rgba(0, 0, 0, 1)"> busy) {
        </span><span style="color: rgba(0, 0, 255, 1)">this</span>.busy =<span style="color: rgba(0, 0, 0, 1)"> busy;
    }
}

}

ConnectionPoolUtils

/*连接池工具类，返回唯一的一个数据库连接池对象, 单例模式*/
public class ConnectionPoolUtils {
    private ConnectionPoolUtils(){}; //私有静态方法
    private static ConnectionPool poolInstance = null;
    public static ConnectionPool GetPoolInstance() {
        if(poolInstance == null) {
            poolInstance = new ConnectionPool(
                "com.mysql.jdbc.Driver",
                "jdbc:mysql://localhost:3306/test?useUnicode=true&characterEncoding=utf-8",
                "root", "123456");
            try {poolInstance.createPool();
            } catch (Exception e) {
                // TODO Auto-generated catch block
                e.printStackTrace();}
        }
        return poolInstance;
    }
}

ConnectionPoolTest

import java.sql.Connection;
import java.sql.DriverManager;
import java.sql.ResultSet;
import java.sql.SQLException;
import java.sql.Statement;
public class ConnectionTest {
</span><span style="color: rgba(0, 128, 0, 1)">/**</span><span style="color: rgba(0, 128, 0, 1)">
 * </span><span style="color: rgba(128, 128, 128, 1)">@param</span><span style="color: rgba(0, 128, 0, 1)"> args
 * </span><span style="color: rgba(128, 128, 128, 1)">@throws</span><span style="color: rgba(0, 128, 0, 1)"> Exception
 </span><span style="color: rgba(0, 128, 0, 1)">*/</span>
<span style="color: rgba(0, 0, 255, 1)">public</span> <span style="color: rgba(0, 0, 255, 1)">static</span> <span style="color: rgba(0, 0, 255, 1)">void</span> main(String[] args) <span style="color: rgba(0, 0, 255, 1)">throws</span><span style="color: rgba(0, 0, 0, 1)"> Exception {
    </span><span style="color: rgba(0, 0, 255, 1)">try</span><span style="color: rgba(0, 0, 0, 1)"> {
        </span><span style="color: rgba(0, 128, 0, 1)">/*</span><span style="color: rgba(0, 128, 0, 1)">使用连接池创建100个连接的时间</span><span style="color: rgba(0, 128, 0, 1)">*/</span>
        <span style="color: rgba(0, 128, 0, 1)">/*</span><span style="color: rgba(0, 128, 0, 1)">// 创建数据库连接库对象
        ConnectionPool connPool = new ConnectionPool("com.mysql.jdbc.Driver","jdbc:mysql://localhost:3306/test", "root", "123456");
        // 新建数据库连接库
        connPool.createPool();</span><span style="color: rgba(0, 128, 0, 1)">*/</span><span style="color: rgba(0, 0, 0, 1)">

        ConnectionPool  connPool</span>=ConnectionPoolUtils.GetPoolInstance();<span style="color: rgba(0, 128, 0, 1)">//</span><span style="color: rgba(0, 128, 0, 1)">单例模式创建连接池对象
        </span><span style="color: rgba(0, 128, 0, 1)">//</span><span style="color: rgba(0, 128, 0, 1)"> SQL测试语句</span>
        String sql = "Select * from pet"<span style="color: rgba(0, 0, 0, 1)">;
        </span><span style="color: rgba(0, 128, 0, 1)">//</span><span style="color: rgba(0, 128, 0, 1)"> 设定程序运行起始时间</span>
        <span style="color: rgba(0, 0, 255, 1)">long</span> start =<span style="color: rgba(0, 0, 0, 1)"> System.currentTimeMillis();
        </span><span style="color: rgba(0, 128, 0, 1)">//</span><span style="color: rgba(0, 128, 0, 1)"> 循环测试100次数据库连接</span>
        <span style="color: rgba(0, 0, 255, 1)">for</span> (<span style="color: rgba(0, 0, 255, 1)">int</span> i = 0; i &lt; 100; i++<span style="color: rgba(0, 0, 0, 1)">) {
            Connection conn </span>= connPool.getConnection(); <span style="color: rgba(0, 128, 0, 1)">//</span><span style="color: rgba(0, 128, 0, 1)"> 从连接库中获取一个可用的连接</span>
            Statement stmt =<span style="color: rgba(0, 0, 0, 1)"> conn.createStatement();
            ResultSet rs </span>=<span style="color: rgba(0, 0, 0, 1)"> stmt.executeQuery(sql);
            </span><span style="color: rgba(0, 0, 255, 1)">while</span><span style="color: rgba(0, 0, 0, 1)"> (rs.next()) {
                String name </span>= rs.getString("name"<span style="color: rgba(0, 0, 0, 1)">);
                </span><span style="color: rgba(0, 128, 0, 1)">//</span><span style="color: rgba(0, 128, 0, 1)">  System.out.println("查询结果" + name);</span>

                }
rs.close();
stmt.close();
connPool.returnConnection(conn);// 连接使用完后释放连接到连接池
            }
System.out.println("经过 100 次的循环调用，使用连接池花费的时间:"+ (System.currentTimeMillis() - start) + "ms");
// connPool.refreshConnections();//刷新数据库连接池中所有连接，即不管连接是否正在运行，都把所有连接都释放并放回到连接池。注意：这个耗时比较大。
connPool.closeConnectionPool();// 关闭数据库连接池。注意：这个耗时比较大。
// 设定程序运行起始时间
start = System.currentTimeMillis();
        </span><span style="color: rgba(0, 128, 0, 1)">/*</span><span style="color: rgba(0, 128, 0, 1)">不使用连接池创建100个连接的时间</span><span style="color: rgba(0, 128, 0, 1)">*/</span>
        <span style="color: rgba(0, 128, 0, 1)">//</span><span style="color: rgba(0, 128, 0, 1)"> 导入驱动</span>
        Class.forName("com.mysql.jdbc.Driver"<span style="color: rgba(0, 0, 0, 1)">);
        </span><span style="color: rgba(0, 0, 255, 1)">for</span> (<span style="color: rgba(0, 0, 255, 1)">int</span> i = 0; i &lt; 100; i++<span style="color: rgba(0, 0, 0, 1)">) {
            </span><span style="color: rgba(0, 128, 0, 1)">//</span><span style="color: rgba(0, 128, 0, 1)"> 创建连接</span>
            Connection conn =<span style="color: rgba(0, 0, 0, 1)"> DriverManager.getConnection(
                </span>"jdbc:mysql://localhost:3306/test", "root", "123456"<span style="color: rgba(0, 0, 0, 1)">);
            Statement stmt </span>=<span style="color: rgba(0, 0, 0, 1)"> conn.createStatement();
            ResultSet rs </span>=<span style="color: rgba(0, 0, 0, 1)"> stmt.executeQuery(sql);
            </span><span style="color: rgba(0, 0, 255, 1)">while</span><span style="color: rgba(0, 0, 0, 1)"> (rs.next()) {
            }
            rs.close();
            stmt.close();
            conn.close();</span><span style="color: rgba(0, 128, 0, 1)">//</span><span style="color: rgba(0, 128, 0, 1)"> 关闭连接</span>

            }
System.out.println("经过 100 次的循环调用，不使用连接池花费的时间:"
+ (System.currentTimeMillis() - start) + "ms");
} catch (SQLException e) {
e.printStackTrace();
} catch (ClassNotFoundException e) {
e.printStackTrace();
}
}
}

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