import java.sql.*;
import java.util.Enumeration;
import java.util.Vector;
public class ConnectionPool {
</span><span style="color: rgba(0, 0, 255, 1)">private</span> String jdbcDriver = ""; <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 dbUrl = ""; <span style="color: rgba(0, 128, 0, 1)">//</span><span style="color: rgba(0, 128, 0, 1)"> 数据 URL</span>

<span style="color: rgba(0, 0, 255, 1)">private</span> String dbUsername = ""; <span style="color: rgba(0, 128, 0, 1)">//</span><span style="color: rgba(0, 128, 0, 1)"> 数据库用户名</span>

<span style="color: rgba(0, 0, 255, 1)">private</span> String dbPassword = ""; <span style="color: rgba(0, 128, 0, 1)">//</span><span style="color: rgba(0, 128, 0, 1)"> 数据库用户密码</span>

<span style="color: rgba(0, 0, 255, 1)">private</span> String testTable = ""; <span style="color: rgba(0, 128, 0, 1)">//</span><span style="color: rgba(0, 128, 0, 1)"> 测试连接是否可用的测试表名，默认没有测试表</span>

<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, 0, 255, 1)">try</span><span style="color: rgba(0, 0, 0, 1)"> {
        createPool();
    } </span><span style="color: rgba(0, 0, 255, 1)">catch</span><span style="color: rgba(0, 0, 0, 1)"> (Exception e) {
        e.printStackTrace();
    }

}

</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)">
 * 用于设置初始连接池中连接的数量
 * </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
 * &lt;p&gt;
 * 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>


        }
    </span><span style="color: rgba(0, 128, 0, 1)">//</span><span style="color: rgba(0, 128, 0, 1)"> 实例化 JDBC Driver 中指定的驱动类实例</span>


        Driver driver = (Driver) (Class.forName(this.jdbcDriver).newInstance());
    DriverManager.registerDriver(driver); </span><span style="color: rgba(0, 128, 0, 1)">//</span><span style="color: rgba(0, 128, 0, 1)"> 注册 JDBC 驱动程序

    </span><span style="color: rgba(0, 128, 0, 1)">//</span><span style="color: rgba(0, 128, 0, 1)"> 创建保存连接的向量 , 初始时有 0 个元素</span>


        connections = new Vector();
    </span><span style="color: rgba(0, 128, 0, 1)">//</span><span style="color: rgba(0, 128, 0, 1)"> 根据 initialConnections 中设置的值，创建连接。</span>


        createConnections(this.initialConnections);
    System.out.println(</span>" 数据库连接池创建成功！ "<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)">
 * 创建由 numConnections 指定数目的数据库连接 , 并把这些连接
 * &lt;p&gt;
 * 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();

        }

        System.out.println(</span>" 数据库连接己创建 ......"<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)">
 * 创建一个新的数据库连接并返回它
 *
 * </span><span style="color: rgba(128, 128, 128, 1)">@return</span><span style="color: rgba(0, 128, 0, 1)"> 返回一个新创建的数据库连接
 </span><span style="color: rgba(0, 128, 0, 1)">*/</span>

<span style="color: rgba(0, 0, 255, 1)">private</span> Connection newConnection() <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)"> 创建一个数据库连接</span>


        Connection conn = DriverManager.getConnection(dbUrl, dbUsername,
                dbPassword);
    </span><span style="color: rgba(0, 128, 0, 1)">//</span><span style="color: rgba(0, 128, 0, 1)"> 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

    </span><span style="color: rgba(0, 128, 0, 1)">//</span><span style="color: rgba(0, 128, 0, 1)"> 最大客户连接数目

    </span><span style="color: rgba(0, 128, 0, 1)">//</span><span style="color: rgba(0, 128, 0, 1)">connections.size()==0 表示目前没有连接己被创建</span>

    <span style="color: rgba(0, 0, 255, 1)">if</span> (connections.size() == 0<span style="color: rgba(0, 0, 0, 1)">) {

        DatabaseMetaData metaData </span>=<span style="color: rgba(0, 0, 0, 1)"> conn.getMetaData();

        </span><span style="color: rgba(0, 0, 255, 1)">int</span> driverMaxConnections =<span style="color: rgba(0, 0, 0, 1)"> metaData.getMaxConnections();

        </span><span style="color: rgba(0, 128, 0, 1)">//</span><span style="color: rgba(0, 128, 0, 1)"> 数据库返回的 driverMaxConnections 若为 0 ，表示此数据库没有最大

        </span><span style="color: rgba(0, 128, 0, 1)">//</span><span style="color: rgba(0, 128, 0, 1)"> 连接限制，或数据库的最大连接限制不知道

        </span><span style="color: rgba(0, 128, 0, 1)">//</span><span style="color: rgba(0, 128, 0, 1)">driverMaxConnections 为返回的一个整数，表示此数据库允许客户连接的数目

        </span><span style="color: rgba(0, 128, 0, 1)">//</span><span style="color: rgba(0, 128, 0, 1)"> 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

        </span><span style="color: rgba(0, 128, 0, 1)">//</span><span style="color: rgba(0, 128, 0, 1)"> 连接数目为数据库允许的最大数目</span>

        <span style="color: rgba(0, 0, 255, 1)">if</span> (driverMaxConnections &gt; 0
                &amp;&amp; <span style="color: rgba(0, 0, 255, 1)">this</span>.maxConnections &gt;<span style="color: rgba(0, 0, 0, 1)"> driverMaxConnections) {

            </span><span style="color: rgba(0, 0, 255, 1)">this</span>.maxConnections =<span style="color: rgba(0, 0, 0, 1)"> driverMaxConnections;

        }

    }

    </span><span style="color: rgba(0, 0, 255, 1)">return</span> conn; <span style="color: rgba(0, 128, 0, 1)">//</span><span style="color: rgba(0, 128, 0, 1)"> 返回创建的新的数据库连接</span>


    }
</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 ,
 * &lt;p&gt;
 * 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
 * &lt;p&gt;
 * 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 </span>= getFreeConnection(); <span style="color: rgba(0, 128, 0, 1)">//</span><span style="color: rgba(0, 128, 0, 1)"> 获得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, 128, 0, 1)"> 如果目前没有可以使用的连接，即所有的连接都在使用中</span>

    <span style="color: rgba(0, 0, 255, 1)">while</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)"> 等一会再试</span>


            wait(250);
        conn </span>= getFreeConnection(); <span style="color: rgba(0, 128, 0, 1)">//</span><span style="color: rgba(0, 128, 0, 1)"> 重新再试，直到获得可用的连接，如果

        </span><span style="color: rgba(0, 128, 0, 1)">//</span><span style="color: rgba(0, 128, 0, 1)">getFreeConnection() 返回的为 null

        </span><span style="color: rgba(0, 128, 0, 1)">//</span><span style="color: rgba(0, 128, 0, 1)"> 则表明创建一批连接后也不可获得可用连接</span>


        }
    </span><span style="color: rgba(0, 0, 255, 1)">return</span> conn;<span style="color: rgba(0, 128, 0, 1)">//</span><span style="color: rgba(0, 128, 0, 1)"> 返回获得的可用的连接</span>


    }
</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
 * &lt;p&gt;
 * 当前没有可用的数据库连接，本函数则根据 incrementalConnections 设置
 * &lt;p&gt;
 * 的值创建几个数据库连接，并放入连接池中。
 * &lt;p&gt;
 * 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 = 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);
        </span><span style="color: rgba(0, 128, 0, 1)">//</span><span style="color: rgba(0, 128, 0, 1)"> 重新从池中查找是否有可用连接</span>


            conn = 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)"> 如果创建连接后仍获得不到可用的连接，则返回 null</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)">;

        }

    }

    </span><span style="color: rgba(0, 0, 255, 1)">return</span><span style="color: rgba(0, 0, 0, 1)"> 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，
 * &lt;p&gt;
 * 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 = 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 = 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>


            }
    }

    </span><span style="color: rgba(0, 0, 255, 1)">return</span> conn;<span style="color: rgba(0, 128, 0, 1)">//</span><span style="color: rgba(0, 128, 0, 1)"> 返回找到到的可用连接</span>


    }
</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
 * &lt;p&gt;
 * 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(true);
        } </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 = 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);
        </span><span style="color: rgba(0, 0, 255, 1)">return</span> <span style="color: rgba(0, 0, 255, 1)">false</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)"> 连接可用，返回 true</span>

    <span style="color: rgba(0, 0, 255, 1)">return</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)">
 * 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。
 * &lt;p&gt;
 * 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(false);
            </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 = (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>


            }
        </span><span style="color: rgba(0, 128, 0, 1)">//</span><span style="color: rgba(0, 128, 0, 1)"> 关闭此连接，用一个新的连接代替它。</span>


            closeConnection(pConn.getConnection());
        pConn.setConnection(newConnection());

        pConn.setBusy(</span><span style="color: rgba(0, 0, 255, 1)">false</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)">
 * 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>


            }
        </span><span style="color: rgba(0, 128, 0, 1)">//</span><span style="color: rgba(0, 128, 0, 1)">5 秒后直接关闭它</span>


            closeConnection(pConn.getConnection());
        </span><span style="color: rgba(0, 128, 0, 1)">//</span><span style="color: rgba(0, 128, 0, 1)"> 从连接池向量中删除它</span>


            connections.removeElement(pConn);
    }

    </span><span style="color: rgba(0, 128, 0, 1)">//</span><span style="color: rgba(0, 128, 0, 1)"> 置连接池为空</span>


        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
 * &lt;p&gt;
 * 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
 * &lt;p&gt;
 * 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;

    }

}

}

import org.junit.Test;
import zzhiDubboprovider.ConnectionPool;
import java.sql.Connection;
import java.sql.PreparedStatement;
import java.sql.ResultSet;
import java.sql.SQLException;
/**


Created by zhangzhii on 2018/2/22.
*/
public class ConnectionPoolTest {
@Test
public void test1() throws Exception {
 ConnectionPool connPool
         </span>= <span style="color: rgba(0, 0, 255, 1)">new</span> ConnectionPool("com.mysql.jdbc.Driver"<span style="color: rgba(0, 0, 0, 1)">
         , </span>"jdbc:mysql://localhost:3306/test?characterEncoding=utf-8"<span style="color: rgba(0, 0, 0, 1)">
         , </span>"root"<span style="color: rgba(0, 0, 0, 1)">
         , </span>"QAZwsx123"<span style="color: rgba(0, 0, 0, 1)">);


 Connection conn</span>=<span style="color: rgba(0, 0, 255, 1)">null</span><span style="color: rgba(0, 0, 0, 1)">;
 PreparedStatement preparedStatement </span>= <span style="color: rgba(0, 0, 255, 1)">null</span><span style="color: rgba(0, 0, 0, 1)">;
 ResultSet resultSet </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, 0, 255, 1)">try</span><span style="color: rgba(0, 0, 0, 1)"> {
     conn </span>=<span style="color: rgba(0, 0, 0, 1)"> connPool.getConnection();


     String sql </span>= "SELECT * FROM test.employee"<span style="color: rgba(0, 0, 0, 1)">;

     preparedStatement </span>=<span style="color: rgba(0, 0, 0, 1)"> conn.prepareStatement(sql);

     </span><span style="color: rgba(0, 128, 0, 1)">//</span><span style="color: rgba(0, 128, 0, 1)">向数据库发出sql执行查询，查询出结果集</span>
     resultSet =<span style="color: rgba(0, 0, 0, 1)"> preparedStatement.executeQuery();
     </span><span style="color: rgba(0, 128, 0, 1)">//</span><span style="color: rgba(0, 128, 0, 1)">遍历查询结果集</span>
     <span style="color: rgba(0, 0, 255, 1)">while</span><span style="color: rgba(0, 0, 0, 1)"> (resultSet.next()) {
         System.out.println(resultSet.getString(</span>"id") + "  " + resultSet.getString("name") + ":" + resultSet.getString("addrress"<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)"> (Exception e) {
     e.printStackTrace();
 }</span><span style="color: rgba(0, 0, 255, 1)">finally</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)">释放资源</span>
     <span style="color: rgba(0, 0, 255, 1)">if</span>(resultSet!=<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)"> {
             resultSet.close();
         } </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)"> TODO Auto-generated catch block</span>



                    e.printStackTrace();
}
}
if(preparedStatement!=null){
try {
preparedStatement.close();
} catch (SQLException e) {
// TODO Auto-generated catch block
                    e.printStackTrace();
}
}
if(conn!=null){
connPool.returnConnection(conn);
}
    }
}

}

  <dependency>
            <groupId>mysql</groupId>
            <artifactId>mysql-connector-java</artifactId>
        </dependency>