JDBC数据源(DataSource)数据源技术是Java操作数据库的一个很关键技术，流行的持久化框架都离不开数据源的应用。
import org.apache.commons.logging.Log;
import org.apache.commons.logging.LogFactory;
import javax.sql.DataSource;
import java.util.Collections;
import java.util.LinkedList;
import java.sql.Connection;
import java.sql.SQLException;
import java.sql.DriverManager;
import java.io.PrintWriter;
/**
* 一个简单的DataSource实现
*
* @author leizhimin 2010-1-14 0:03:17
*/
public class SimpleDateSource implements DataSource {
private static Log log = LogFactory.getLog(SimpleDateSource.class);
private static final String dirverClassName = "com.mysql.jdbc.Driver";
private static final String url = "jdbc:mysql://127.0.0.1:3306/testdb";
private static final String user = "root";
private static final String pswd = "leizhimin";
//连接池
private static LinkedList<Connection> pool = (LinkedList<Connection>) Collections.synchronizedList(new LinkedList<Connection>());
private static SimpleDateSource instance = new SimpleDateSource();
static {
try {
Class.forName(dirverClassName);
} catch (ClassNotFoundException e) {
log.error("找不到驱动类！", e);
}
}
private SimpleDateSource() {
}
/**
* 获取数据源单例
*
* @return 数据源单例
*/
public SimpleDateSource instance() {
if (instance == null) instance = new SimpleDateSource();
return instance;
}
/**
* 获取一个数据库连接
*
* @return 一个数据库连接
* @throws SQLException
*/
public Connection getConnection() throws SQLException {
synchronized (pool) {
if (pool.size() > 0) return pool.removeFirst();
else return makeConnection();
}
}
/**
* 连接归池
*
* @param conn
*/
public static void freeConnection(Connection conn) {
pool.addLast(conn);
}
private Connection makeConnection() throws SQLException {
return DriverManager.getConnection(url, user, pswd);
}
public Connection getConnection(String username, String password) throws SQLException {
return DriverManager.getConnection(url, username, password);
}
public PrintWriter getLogWriter() throws SQLException {
return null;
}
public void setLogWriter(PrintWriter out) throws SQLException {
}
public void setLoginTimeout(int seconds) throws SQLException {
}
public int getLoginTimeout() throws SQLException {
return 0;
}
public <T> T unwrap(Class<T> iface) throws SQLException {
return null;
}
public boolean isWrapperFor(Class<?> iface) throws SQLException {
return false;
}
}
DataSource接口（javax.sql.DataSource）替代DriverManager获取Connection的方法，有以下好处：
- 可以在部署时灵活更换Connection实现；
- 可以更好的屏蔽数据库的相关性。
以下以Oracle为例说明。
使用厂商DataSource
数据库厂商在提高JDBC2.0和以上版本的JDBC驱动中应该包含厂商的DataSource实现。
OracleDataSource ods = new OracleDataSource();
ods.setUser(“my_user”);
ods.setPassword(“my_password”);
ods.setURL(“jdbc:oracle:thin:@<database>”);
Connection conn = ods.getConnection();
第三方DataSource
第三方厂商也可提供DataSource实现，比如免费开源的有DBCP，C3P0和proxool等，中间件厂商比如ibm的websphere，bea的weblogic等也都有实现。
以下是DBCP的示例：
BasicDataSource basicDataSource = new BasicDataSource(); basicDataSource.setDriverClassName(“oracle.jdbc.OracleDriver”); basicDataSource.setUrl(“jdbc:oracle:thin:@<database>”); basicDataSource.setUsername(“user”);basicDataSource.setPassword(“password”); Connection connection=basicDataSource.getConnection();
结合JNDI的DataSource
以tomcat为例，将数据库驱动库复制到{tomcat}/commmon/lib目录下。
配置{tomcat}/conf/context.xml文件，加入：
<Resource name=”jdbc/demo” auth=”Container” type=”javax.sql.DataSource”
driverClassName=”org.apache.derby.jdbc.ClientDriver”
url=”jdbc:derby://localhost:1527/demo”
username=”test”
password=”test”
maxActive=”2″
maxIdle=”1″
removeAbandoned=”true”
maxWait=”300″ />
在程序中访问DataSource：
Context initContext = new InitialContext();
// 注意: 以下写法只适用于tomcat(Java:/comp/env).
Context envContext = (Context) initContext.lookup(“java:/comp/env”);
dataSource = (DataSource) envContext.lookup(“jdbc/demo”);
配置内容也可以加到webapp/META-INF/context.xml文件中，这样更便于打包部署。
<%@page import="java.sql.*, javax.sql.*, javax.naming.*"%>
<html>
<head>
<title>Using a DataSource</title>
</head>
<body>
<h1>Using a DataSource</h1>
<%
DataSource ds = null;
Connection conn = null;
ResultSet result = null;
Statement stmt = null;
ResultSetMetaData rsmd = null;
try{
Context context = new InitialContext();
Context envCtx = (Context) context.lookup("java:comp/env");
ds = (DataSource)envCtx.lookup("jdbc/address");
if (ds != null) {
conn = ds.getConnection();
stmt = conn.createStatement();
result = stmt.executeQuery("SELECT * FROM AddressList");
}
}
catch (SQLException e) {
System.out.println("Error occurred " + e);
}
int columns=0;
try {
rsmd = result.getMetaData();
columns = rsmd.getColumnCount();
}
catch (SQLException e) {
System.out.println("Error occurred " + e);
}
%>
<table width="90%" border="1">
<tr>
<% // write out the header cells containing the column labels
try {
for (int i=1; i<=columns; i++) {
out.write("<th>" + rsmd.getColumnLabel(i) + "</th>");
}
%>
</tr>
<% // now write out one row for each entry in the database table
while (result.next()) {
out.write("<tr>");
for (int i=1; i<=columns; i++) {
out.write("<td>" + result.getString(i) + "</td>");
}
out.write("</tr>");
}
// close the connection, resultset, and the statement
result.close();
stmt.close();
conn.close();
} // end of the try block
catch (SQLException e) {
System.out.println("Error " + e);
}
// ensure everything is closed
finally {
try {
if (stmt != null)
stmt.close();
} catch (SQLException e) {}
try {
if (conn != null)
conn.close();
} catch (SQLException e) {}
}
%>
</table>
</body>
</html>
