使用Jet的JNDI查找失败与MySQL建立JDBC连接池？ [英] JNDI lookup failing with Jetty for JDBC connection pooling with MySQL?

问题描述

我正在使用带有标准MySQL连接器API的Jetty 9.2（嵌入式），我对如何设置它感到困惑。目前，我在 web.xml 文件中有这个：

I'm using Jetty 9.2 (embedded) with the standard MySQL connector API and I'm very confused by how this is supposed to be setup. Currently, I have this in my web.xml file:

<webapp ...

    <resource-ref>
        <description>JDBC Data Source</description>
        <res-ref-name>jdbc/DataSource</res-ref-name>
        <res-type>javax.sql.DataSource</res-type>
        <res-auth>Container</res-auth>
    </resource-ref>
</webapp>

...这在我的jetty-env.xml中：

<Configure class="org.eclipse.jetty.webapp.WebAppContext">

   <New id="DatabaseConnector" class="org.eclipse.jetty.plus.jndi.Resource">
        <Arg></Arg>
        <Arg>jdbc/DataSource</Arg>
        <Arg>
            <New class="com.mysql.jdbc.jdbc2.optional.MysqlConnectionPoolDataSource">
                <Set name="Url">jdbc:mysql://localhost:3306/DBName</Set>
                <Set name="User">user</Set>
                <Set name="Password">pass</Set>
            </New>
        </Arg>
    </New>

 </Configure>

...此代码初始化：

Context envCtx = (Context) new InitialContext().lookup("java:comp/env");
DataSource datasource = (DataSource) envCtx.lookup("jdbc/DataSource");

当我尝试启动服务器时，我收到错误 javax。 naming.NameNotFoundException;剩余名称'jdbc / DataSource'。我在代码初始化中尝试了很多不同的字符串变体，比如在 InitialContext上删除 lookup 调用对象，但我只是使用不同的名称值继续得到相同错误的变体;

When I try to fire up the server, I get the error javax.naming.NameNotFoundException; remaining name 'jdbc/DataSource'. I've tried lots of different variations of the strings in the code initialization, like removing the lookup call on the InitialContext object, but I just keep getting variations of the same error with a different name value;

两个xml文件位于我的 / WAR / WEB-INF 目录中。我看过很多以前的问题和教程，博客等，但我无处可去。

Both of the xml files are located in my /WAR/WEB-INF directory. I've looked at loads of previous questions and tutorials, blogs etc. but I'm getting nowhere.

推荐答案

这是一个嵌入式Jetty特有的问题组合。

It was a combination of problems specific to embedded Jetty.

首先，配置和启动Web服务器的启动器代码在我实际启动Web服务器之前进行JNDI查找，即在调用服务器之前.start（），因此JNDI配置在该阶段未初始化。

First, my launcher code that was configuring and launching the web server was doing the JNDI lookup before I actually started the web server i.e. before calling server.start(), so the JNDI configuration was not initialized at that stage.

但即使进行此更改也不起作用，因为需要从与WebApp关联的线程调用 envCtx.lookup（jdbc / DataSource）。所以我将该代码移动到静态块，在第一次Web服务器请求请求数据库连接时调用该块。

But even making this change didn't work, because the envCtx.lookup("jdbc/DataSource") needs to be called from a thread that's associated with the WebApp. So I moved that code to a static block that gets called the first time a database connection is requested by a web server request.

最后，我最终得到了一些东西对于我的启动器代码是这样的：

In the end, I ended up with something like this for my launcher code:

public static void main(String[] args) {
    Server server = new Server();

    //Enable parsing of jndi-related parts of web.xml and jetty-env.xml
    ClassList classlist = ClassList.setServerDefault(server);
    classlist.addAfter(
            "org.eclipse.jetty.webapp.FragmentConfiguration", 
            "org.eclipse.jetty.plus.webapp.EnvConfiguration", 
            "org.eclipse.jetty.plus.webapp.PlusConfiguration");
...
...
server.start();

这个主线程不能进行JNDI查找，所以把它放在像<$ c $这样的地方c> init servlet请求的方法，或者像我所做的那样，servlet使用的静态数据库访问器类的同步方法，例如

The JNDI lookup cannot be made by this main thread, so put it somewhere like the init method of a servlet request, or like I did, a synchronized method of a static database accessor class that gets used by servlets e.g.

public class DatabaseUtils {

    private static DataSource datasource;

    private static synchronized Connection getDBConnection() throws SQLException {
        if (datasource == null) {
            initDataSource();
        }
        return datasource.getConnection();
    }

    public static void initDataSource() {
        try {
             datasource = (DataSource) new InitialContext().lookup("java:comp/env/jdbc/DataSource");
             LOG.info("Database connection pool initalized successfully");
        } catch (Exception e) {
            LOG.error("Error while initialising the database connection pool", e);
        }
    }

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