tomcat的 配置，进入conf->context.xml

web中调用

Context c=new InitialContext();
        DataSource ds=(DataSource)c.lookup("java:comp/env/mysql");
         out.println(ds.getConnection());

通过注记获取

@Resource(name="mysql",type=DataSource.class,authenticationType=AuthenticationType.CONTAINER)
public class Test extends HttpServlet {

@Resource(name="mysql")
    private DataSource ds;
    public void doGet(HttpServletRequest request, HttpServletResponse response)
            throws ServletException, IOException {

response.setContentType("text/html");
        PrintWriter out = response.getWriter();
        try {
            Context c=new InitialContext();
            out.println(ds.getConnection().toString());
        } catch (NamingException e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        } catch (SQLException e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        }
        
        out.flush();
        out.close();
    }