Question

我正在尝试确定我是否实际使用JDBC连接池。经过一些研究，实施几乎看起来太容易了。事实上比常规连接更容易，所以我想验证。

这是我的连接类：

public class DatabaseConnection {

Connection conn = null;

public Connection getConnection() {

    BasicDataSource bds = new BasicDataSource();
    bds.setDriverClassName("com.mysql.jdbc.Driver");
    bds.setUrl("jdbc:mysql://localhost:3306/data");
    bds.setUsername("USERNAME");
    bds.setPassword("PASSWORD");

    try{
        System.out.println("Attempting Database Connection");
        conn = bds.getConnection();
        System.out.println("Connected Successfully");
    }catch(SQLException e){
        System.out.println("Caught SQL Exception: " + e);
    }
    return conn;
}

public void closeConnection() throws SQLException {
    conn.close();
}

}

这是真正的连接汇集吗？我在另一个类中使用连接：

        //Check data against database.
    DatabaseConnection dbConn = new DatabaseConnection();
    Connection conn;
    ResultSet rs;
    PreparedStatement prepStmt;

    //Query database and check username/pass against table.
    try{
        conn = dbConn.getConnection();
        String sql = "SELECT * FROM users WHERE username=? AND password=?";
        prepStmt = conn.prepareStatement(sql);
        prepStmt.setString(1, user.getUsername());
        prepStmt.setString(2, user.getPassword());
        rs = prepStmt.executeQuery();

        if(rs.next()){ //Found Match.
            do{
                out.println("UserName = " + rs.getObject("username") + " Password = " + rs.getObject("password"));
                out.println("<br>");
            } while(rs.next());
        } else {
            out.println("Sorry, you are not in my database."); //No Match.
        }

        dbConn.closeConnection(); //Close db connection.

    }catch(SQLException e){
        System.out.println("Caught SQL Exception: " + e);
    }

Answer 1

假设BasicDataSource来自DBCP，那么是的，您正在使用连接池。但是，您要在每个连接获取上重新创建另一个连接池。您实际上并不是从同一个池中汇集连接。您只需在应用程序启动时创建一次连接池，并从中获取每个连接。您也不应该将连接保存为实例变量。您还应关闭连接，语句和结果集，以确保在异常情况下正确关闭资源。 Java 7 try-with-resources statement对此有帮助，它将在try块完成时自动关闭资源。

这是一个小改写：

public final class Database {

    private static final BasicDataSource dataSource = new BasicDataSource();

    static {
        dataSource.setDriverClassName("com.mysql.jdbc.Driver");
        dataSource.setUrl("jdbc:mysql://localhost:3306/data");
        dataSource.setUsername("USERNAME");
        dataSource.setPassword("PASSWORD");
    }

    private Database() {
        //
    }

    public static Connection getConnection() throws SQLException {
        return dataSource.getConnection();
    }

}

（如果有必要，可以将其重构为抽象工厂以提高可插拔性）

和

private static final String SQL_EXIST = "SELECT * FROM users WHERE username=? AND password=?";

public boolean exist(User user) throws SQLException {
    boolean exist = false;

    try (
        Connection connection = Database.getConnection();
        PreparedStatement statement = connection.prepareStatement(SQL_EXIST);
    ) {
        statement.setString(1, user.getUsername());
        statement.setString(2, user.getPassword());

        try (ResultSet resultSet = preparedStatement.executeQuery()) {
            exist = resultSet.next();
        }
    }       

    return exist;
}

使用如下：

try {
    if (!userDAO.exist(username, password)) {
        request.setAttribute("message", "Unknown login. Try again.");
        request.getRequestDispatcher("/WEB-INF/login.jsp").forward(request, response);
    } else {
        request.getSession().setAttribute("user", username);
        response.sendRedirect("userhome");
    }
} catch (SQLException e) {
    throw new ServletException("DB error", e);
}

在真正的Java EE环境中，您应该将DataSource的创建委托给容器/应用程序服务器并从JNDI获取它。如果是Tomcat，请参阅此文档：http://tomcat.apache.org/tomcat-6.0-doc/jndi-resources-howto.html

Answer 2

看起来好像没有合并。您应该将DataSource存储在DatabaseConnection中，而不是在每次getConnection（）调用时创建一个新的。 getConnection（）应该返回datasource.getConnection（）。

Answer 3

看起来像DBCP用法。如果是，那么是的。它已经汇集了。这是DBCP的默认池属性值。

/**
* The default cap on the number of "sleeping" instances in the pool.
* @see #getMaxIdle
* @see #setMaxIdle
*/
public static final int DEFAULT_MAX_IDLE  = 8;
/**
* The default minimum number of "sleeping" instances in the pool
* before before the evictor thread (if active) spawns new objects.
* @see #getMinIdle
* @see #setMinIdle
*/
public static final int DEFAULT_MIN_IDLE = 0;
/**
* The default cap on the total number of active instances from the pool.
* @see #getMaxActive
*/
public static final int DEFAULT_MAX_ACTIVE  = 8;

Answer 4

作为BalusC解决方案的后续，下面是一个实现，我可以在需要多个连接的应用程序中使用，或者在一个不会提前知道连接属性的公共库中使用...

import org.apache.commons.dbcp.BasicDataSource;

import java.sql.Connection;
import java.sql.SQLException;
import java.util.concurrent.ConcurrentHashMap;

public final class Database {

    private static final ConcurrentHashMap<String, BasicDataSource> dataSources = new ConcurrentHashMap();

    private Database() {
        //
    }

    public static Connection getConnection(String connectionString, String username, String password) throws SQLException {

        BasicDataSource dataSource;

        if (dataSources.containsKey(connectionString)) {
            dataSource = dataSources.get(connectionString);
        } else {
            dataSource = new BasicDataSource();
            dataSource.setDriverClassName("com.mysql.jdbc.Driver");
            dataSource.setUrl(connectionString);
            dataSource.setUsername(username);
            dataSource.setPassword(password);
            dataSources.put(connectionString, dataSource);
        }

        return dataSource.getConnection();

    }

}

我使用JDBC连接池吗？

4 个答案: