JAVA与关系形数据库

JDBC

JDBC是JDK提供的JAVA访问关系型数据库的SPI，有多种实现方式。

ODBC是微软提出的！O是open不是oracle。也是最造被开发者和数据库厂商接收的交互方案。所以可以在ODBC的基础上构建JDBC，称为JDBC-ODBC Bridge Driver。ODBC通过调用数据库的本地客户端的API和远程数据库通信交互。

当然，可以直接调用数据库本地的客户端。也就是Native API Driver。不过，JDBC实现者就无法做到硬件无关了。所以，不被推荐。

JDBC-Net Driver,Java将sql翻译为数据库无关的操作协议，发给中间服务器，中间服务器负责翻译为具体服务器的操作转发到数据库服务器。ADO.NET是使用这种方案的。

Native Protocol Driver 最常用的一种，JDBC实现者直接将命令转化为操作数据的网络请求，直接发送给数据库。mysql-connector-java就属于这一种。

JDBC对数据库操作基本如下

      //加载驱动
      Class.forName("com.mysql.jdbc.Driver");
      System.out.println("Connecting to database...");
      //建立连接
      conn = DriverManager.getConnection(DB_URL,USER,PASS);

      //执行SQL
      System.out.println("Creating statement...");
      stmt = conn.createStatement();
      String sql;
      sql = "SELECT id, first, last, age FROM Employees";
      ResultSet rs = stmt.executeQuery(sql);

      //分析结果
      while(rs.next()){
         //Retrieve by column name
         int id  = rs.getInt("id");
         int age = rs.getInt("age");
      }

JNDI

JNDI可以配置在诸如Tomcat这样的容器中。提供程序员数据访问，而开发者不需要在代码里关系数据访问的细节。以tomcat为例，server.xml配置文件如下,配置两个数据源

 <!-- Global JNDI resources
       Documentation at /docs/jndi-resources-howto.html
  -->
  <GlobalNamingResources>
    <!-- Editable user database that can also be used by
         UserDatabaseRealm to authenticate users
    -->
    <Resource name="UserDatabase" auth="Container"
              type="org.apache.catalina.UserDatabase"
              description="User database that can be updated and saved"
              factory="org.apache.catalina.users.MemoryUserDatabaseFactory"
              pathname="conf/tomcat-users.xml" />
<Resource name="UserDatabase" auth="Container"
              type="org.apache.catalina.UserDatabase"
              description="User database that can be updated and saved"
              factory="org.apache.catalina.users.MemoryUserDatabaseFactory"
              pathname="conf/tomcat-users.xml" />


<Resource auth="Container" 
             description="DB Connection" 
             driverClass="oracle.jdbc.driver.OracleDriver" 
             maxPoolSize="20" 
             minPoolSize="5" 
             acquireIncrement="5" 
             maxIdleTime="300"
             idleConnectionTestPeriod="60"
             automaticTestTable="Test"
             acquireRetryAttempts="30"
             breakAfterAcquireFailure="true"
             name="jdbc/amodMonDbSource"
             user="amod" 
             password="amoddb" 
             factory="org.apache.naming.factory.BeanFactory" 
             type="com.mchange.v2.c3p0.ComboPooledDataSource" 
             jdbcUrl="jdbc:oracle:thin:@10.111.0.108:1521:orcl" />


<Resource auth="Container" 
             description="DB Connection" 
             driverClass="oracle.jdbc.driver.OracleDriver" 
             maxPoolSize="20" 
             minPoolSize="5" 
             acquireIncrement="5" 
             maxIdleTime="300"
             idleConnectionTestPeriod="60"
             automaticTestTable="Test"
             acquireRetryAttempts="30"
             breakAfterAcquireFailure="true"
             name="jdbc/ddamodMonDbSource"
             user="ddamod" 
             password="ddamoddb" 
             factory="org.apache.naming.factory.BeanFactory" 
             type="com.mchange.v2.c3p0.ComboPooledDataSource" 
             jdbcUrl="jdbc:oracle:thin:@10.111.0.108:1521:orcl" />


  </GlobalNamingResources>

然后还需要在context.xml中进行配置

<!-- The contents of this file will be loaded for each web application -->
<Context>
    <!-- Default set of monitored resources. If one of these changes, the    -->
    <!-- web application will be reloaded.                                   -->
    <WatchedResource>WEB-INF/web.xml</WatchedResource>
    <WatchedResource>${catalina.base}/conf/web.xml</WatchedResource>
    <!-- Uncomment this to disable session persistence across Tomcat restarts -->
    <!--
    <Manager pathname="" />
    -->


<ResourceLink name="jdbc/amodMonDbSource" global="jdbc/amodMonDbSource" type="javax.sql.DataSource"/>
<ResourceLink name="jdbc/ddamodMonDbSource" global="jdbc/ddamodMonDbSource" type="javax.sql.DataSource"/>
</Context>

最后就是实际使用了

Connection conn=null;try {  
Context ctx=new InitialContext();  
Object datasourceRef=ctx.lookup("java:MySqlDS"); 
......  
c.close();
} catch(Exception e) {  
e.printStackTrace();
} finally {  
if(conn!=null) {    
try {      
conn.close();    
} catch(SQLException e) { }  
}
}