从连接池获取数据库连接 [英] Get database connection from a connection pool

问题描述

我正在重构其他代码。我注意到的一件事是关于系统如何从连接池获得连接的方式。

I am refactoring others code. The one thing I notice is that of the manner on how the system is getting a connection from the connection pool.

示例是这样的。在每次调用service方法时，系统都会在JNDI上为数据源进行上下文查找。

Sample is like this. On every call of the service method, the system is making a context lookup on the JNDI for the datasource.

public class CheckinServlet extends HttpServlet {

    public void doPost(HttpServletRequest request, HttpServletResponse response)
            throws ServletException, IOException {

        try {
            //Obtain Connection
            InitialContext initialContext = new InitialContext();
            javax.sql.DataSource ds = (javax.sql.DataSource) initialContext
                    .lookup("jdbc/mysqldb");
            java.sql.Connection conn = ds.getConnection();
            //business logic
            //redirect
        } finally {
            conn.close();
        }
    }
}

我认为有每次这样做都会影响性能。我正在考虑另外一种方法来解决如何从连接池中检索连接。

I do think that there is a performance hit on doing this every time. I am thinking of another way around these on how to retrieve a connection from a connection pool.

我正在考虑使用servlet的 init（） 方法，但我认为这不是最优的。

I am thinking about using the servlet's init() method but I think that is not optimal.

推荐答案

在 ServletContextListener 每次在 init（）中的许多servlet。在webapp启动期间， contextInitialized（）方法只执行一次。

Do it once in a ServletContextListener instead of everytime in init() of many servlets. The contextInitialized() method is executed only once during webapp's startup.

public class Config implements ServletContextListener {
    private static final String ATTRIBUTE_NAME = "config";
    private DataSource dataSource;

    @Override
    public void contextInitialized(ServletContextEvent event) {
        ServletContext servletContext = event.getServletContext();
        String databaseName = servletContext.getInitParameter("database.name");
        try {
            dataSource = (DataSource) new InitialContext().lookup(databaseName);
        } catch (NamingException e) {
            throw new RuntimeException("Config failed: datasource not found", e);
        }
        servletContext.setAttribute(ATTRIBUTE_NAME, this);
    }

    @Override
    public void contextDestroyed(ServletContextEvent event) {
        // NOOP.
    }

    public DataSource getDataSource() {
        return dataSource;
    }

    public static Config getInstance(ServletContext servletContext) {
        return (Config) servletContext.getAttribute(ATTRIBUTE_NAME);
    }
}

在中按如下方式配置web.xml ：

<context-param>
    <param-name>database.name</param-name>
    <param-value>jdbc/mysqldb</param-value>
</context-param>
<listener>
    <listener-class>com.example.Config</listener-class>
</listener>

您可以在servlet中获取它，如下所示（ init（）或 doXXX（）方法，您选择）：

You can obtain it in your servlet as follows (init() or doXXX() method, you choose):

DataSource dataSource = Config.getInstance(getServletContext()).getDataSource();

然而，我会进一步重构它，最好将JDBC代码放在自己的类中，不在servlet中。查看DAO模式。

I'd however refactor it a step further, JDBC code should preferably be placed in its own classes, not in servlets. Lookup the DAO pattern.

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