JNDI多数据源实现方案
目的：
实现多数据源的配置访问。
配置文件示例：
<id="querycodedict" ds="sysds"> select * from code_dict</id>
本文并没有使用此配置文件进行模拟，但整个过程完全相似，如果以此配置文件为准，需要编写对此文件的解析过程
服务器：
tomcat5.5
数据库：
mysql5.0
准备：
建立两个数据库
数据库1:javatest
mysql> GRANT ALL PRIVILEGES ON *.* TO javauser@localhost IDENTIFIED BY 'javadude' WITH GRANT OPTION;
mysql> create database javatest;
mysql> use javatest;
mysql> create table testdata (
-> id int not null auto_increment primary key,
-> foo varchar(25),
-> bar int);
mysql> insert into testdata values(null, 'hello', 12345);
Query OK, 1 row affected (0.00 sec)
mysql> select * from testdata;
+----+-------+-------+
| ID | FOO | BAR |
+----+-------+-------+
| 1 | hello | 12345 |
+----+-------+-------+
1 row in set (0.00 sec)
mysql>
数据库2：systest
mysql> GRANT ALL PRIVILEGES ON *.* TO sysuser@localhost IDENTIFIED BY 'javadude' WITH GRANT OPTION;
Query OK, 0 rows affected (0.06 sec)
mysql> create database systest;
Query OK, 1 row affected (0.02 sec)
mysql> use systest;
Database changed
mysql> create table code_dict(
-> id int not null auto_increment primary key,
-> foo varchar(25),
-> bar int);
Query OK, 0 rows affected (0.14 sec)
mysql> insert into code_dict values(null, 'hello', 12345);
Query OK, 1 row affected (0.05 sec)
mysql> select * from code_dict;
+----+-------+-------+
| id | foo | bar |
+----+-------+-------+
| 1 | hello | 12345 |
+----+-------+-------+
1 row in set (0.00 sec)
mysql>
编写配置文件：
tomcat家目录下有conf文件夹，其中有一个context.xml文件
配置如下：
<!-- The contents of this file will be loaded for each web application --> <Context path="/DBTest" docBase="DBTest" debug="5" reloadable="true" crossContext="true"> <Resource name="jdbc/TestDB" auth="Container" type="javax.sql.DataSource" maxActive="100" maxIdle="30" maxWait="10000" username="javauser" password="javadude" driverClassName="com.mysql.jdbc.Driver" url="jdbc:mysql://localhost:3306/javatest?autoReconnect=true"/> <Resource name="jdbc/SysDB" auth="Container" type="javax.sql.DataSource" maxActive="100" maxIdle="30" maxWait="10000" username="sysuser" password="javadude" driverClassName="com.mysql.jdbc.Driver" url="jdbc:mysql://localhost:3306/systest?autoReconnect=true"/></Context>
添加jbdc驱动：
tomcat家目录下有common文件夹，将mysq驱动放入其中的lib下
编写代码测试：
建立一个web工程，编写一个servlet进行测试
web.xml文件配置如下：
<?xml version="1.0" encoding="UTF-8"?>
<web-app version="2.5"
xmlns="http://java.sun.com/xml/ns/javaee"
xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xsi:schemaLocation="http://java.sun.com/xml/ns/javaee
http://java.sun.com/xml/ns/javaee/web-app_2_5.xsd">
<servlet>
<servlet-name>JNDIServlet</servlet-name>
<servlet-class>JNDIServlet</servlet-class>
</servlet>
<servlet-mapping>
<servlet-name>JNDIServlet</servlet-name>
<url-pattern>/servlet/JNDIServlet</url-pattern>
</servlet-mapping>
<description>MySQL Test App</description>
<resource-ref>
<description>DB Connection</description>
<res-ref-name>jdbc/TestDB</res-ref-name>
<res-type>javax.sql.DataSource</res-type>
<res-auth>Container</res-auth>
</resource-ref>
<resource-ref>
<description>DB Connection</description>
<res-ref-name>jdbc/SysDB</res-ref-name>
<res-type>javax.sql.DataSource</res-type>
<res-auth>Container</res-auth>
</resource-ref>
<welcome-file-list>
<welcome-file>index.jsp</welcome-file>
</welcome-file-list>
</web-app>
编写java代码，JNDIBinding类中的代码在servlet中doGet方法中调用
import java.io.IOException;
import java.io.PrintWriter;
import java.sql.SQLException;
import javax.naming.NamingException;
import javax.servlet.ServletException;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
public class JNDIServlet extends HttpServlet
{
/**
* The doGet method of the servlet. <br>
*
* This method is called when a form has its tag value method equals to get.
*
* @param request the request send by the client to the server
* @param response the response send by the server to the client
* @throws ServletException if an error occurred
* @throws IOException if an error occurred
*/
public void doGet(HttpServletRequest request, HttpServletResponse response)
throws ServletException, IOException
{
response.setContentType("text/html");
PrintWriter out = response.getWriter();
out
.println("<!DOCTYPE HTML PUBLIC /"-//W3C//DTD HTML 4.01 Transitional//EN/">");
out.println("<HTML>");
out.println(" <HEAD><TITLE>A Servlet</TITLE></HEAD>");
out.println(" <BODY>");
out.print(" This is ");
out.print(this.getClass());
out.println(", using the GET method");
try
{out.println("get JNDI");
JNDIBinding.getJNDI(request.getParameter("name"));
} catch (NamingException e)
{
// TODO Auto-generated catch block
e.printStackTrace();
} catch (SQLException e)
{
// TODO Auto-generated catch block
e.printStackTrace();
}
out.println(" </BODY>");
out.println("</HTML>");
out.flush();
out.close();
}
/**
* The doPost method of the servlet. <br>
*
* This method is called when a form has its tag value method equals to post.
*
* @param request the request send by the client to the server
* @param response the response send by the server to the client
* @throws ServletException if an error occurred
* @throws IOException if an error occurred
*/
public void doPost(HttpServletRequest request, HttpServletResponse response)
throws ServletException, IOException
{
response.setContentType("text/html");
PrintWriter out = response.getWriter();
out
.println("<!DOCTYPE HTML PUBLIC /"-//W3C//DTD HTML 4.01 Transitional//EN/">");
out.println("<HTML>");
out.println(" <HEAD><TITLE>A Servlet</TITLE></HEAD>");
out.println(" <BODY>");
out.print(" This is ");
out.print(this.getClass());
out.println(", using the POST method");
try
{out.println("get JNDI");
JNDIBinding.getJNDI(request.getParameter("name"));
} catch (NamingException e)
{
// TODO Auto-generated catch block
e.printStackTrace();
} catch (SQLException e)
{
// TODO Auto-generated catch block
e.printStackTrace();
}
out.println(" </BODY>");
out.println("</HTML>");
out.flush();
out.close();
}
}
import java.sql.Connection;
import java.sql.ResultSet;
import java.sql.SQLException;
import java.sql.Statement;
import javax.naming.Context;
import javax.naming.InitialContext;
import javax.naming.NamingException;
import javax.sql.DataSource;
/***
*
* 设想方案：
* 多个数据库
* 同一个配置文件中可以编写不同数据源的sql在其中
* 代码中指明sql的名称，根据名称得到数据源标识及对应sql
* 根据数据源标识得到相应的数据库连接，之后即可对相应的数据库进行操作
*
* 配置文件示例：
* <id="querycodedict" ds="sysds"> select * from code_dict</id>
*
* @author Administrator
*
*/
public class JNDIBinding
{
/***
* 以下代码很简单的模拟了根据传入数据不同得到不同数据库连接，进行不同的操作
* @param obj
* @throws NamingException
* @throws SQLException
*/
static void getJNDI(Object obj) throws NamingException, SQLException
{
System.out.println(obj);
Context initContext = new InitialContext();
//两个不同的数据源配置
String ardb = "jdbc/TestDB";
String sysdb = "jdbc/SysDB";
String jndi = null;
String sql = null;
//如果传入的参数是123则查询javatest库,不是则查询systest库
if (obj.equals("123"))
{
jndi = ardb;
sql = "select * from testdata";
}
else
{
jndi = sysdb;
sql = "select * from code_dict";
}
//查找数据源
DataSource ds = (DataSource) initContext.lookup("java:/comp/env/"+ jndi);
//获得连接
Connection conn = ds.getConnection();
if (conn == null)
{
System.out.println("conn is null");
return;
} else
{
System.out.println("conn is not null");
}
Statement stmt = null; // Or PreparedStatement if needed
ResultSet rs = null;
try
{
stmt = conn.createStatement();
System.out.println(sql);
rs = stmt.executeQuery(sql);
while (rs != null && rs.next())
{
System.out.println(rs.getInt("id"));
}
rs.close();
rs = null;
stmt.close();
stmt = null;
conn.close(); // Return to connection pool
conn = null; // Make sure we don't close it twice
} catch (SQLException e)
{
e.getStackTrace();
} finally
{
if (rs != null)
{
try
{
rs.close();
} catch (SQLException e)
{
;
}
rs = null;
}
if (stmt != null)
{
try
{
stmt.close();
} catch (SQLException e)
{
;
}
stmt = null;
}
if (conn != null)
{
try
{
conn.close();
} catch (SQLException e)
{
;
}
conn = null;
}
}
}
}
在地址栏中输入以下内容
http://localhost:8081/DBTest/servlet/JNDIServlet?name=123
运行后中控制台中可以看到查询结果
另特别说明：
此过程中遇到过找不到驱动问题，最后看官方文档发现驱动应该放在common目录下的lib下，如在网上找贴学习，此错误容易遇到