java 模板模式+回调+泛型实现数据库查询

一、数据库连接工具类

import java.sql.Connection;
import java.sql.DriverManager;
import java.sql.SQLException;


public class ConnectionUtils {
private final String ORACLE_DRIVER = "oracle.jdbc.driver.OracleDriver";


private final String URL = "jdbc:oracle:thin:@###.###.###.###:1521:****";


private final String USERNAME = "username";


private final String PASSWORD = "password";

private ConnectionUtils(){}

private static class DataBaseHolder{
private static final ConnectionUtils instance = new ConnectionUtils();
}

public static ConnectionUtils getInstance(){
return DataBaseHolder.instance;
}


public Connection getConnectionion() {
Connection conn = null;
try {
Class.forName(ORACLE_DRIVER);
conn = DriverManager.getConnection(URL, USERNAME, PASSWORD);
} catch (ClassNotFoundException e) {
e.printStackTrace();
} catch (SQLException e) {
e.printStackTrace();
}
return conn;
}


}

二、处理ResultSet结果集的公共接口

import java.sql.ResultSet;


public interface ResultSetHandler<T> {
public T handle(ResultSet rs);
}

三、SimpleJdbcTemplate主工具类

import java.sql.Connection;

import java.sql.PreparedStatement;
import java.sql.ResultSet;
import java.sql.SQLException;
import java.sql.Statement;


public class SimpleJdbcTemplate {
public static <T> T query(String queryString, ResultSetHandler<T> rsHandler) {
Connection connection = null;
PreparedStatement stmt = null;
try {
connection = ConnectionUtils.getInstance().getConnectionion();  
stmt = connection.prepareStatement(queryString,ResultSet.TYPE_SCROLL_INSENSITIVE,ResultSet.CONCUR_UPDATABLE);
ResultSet rs = stmt.executeQuery();
return rsHandler.handle(rs);
} catch (SQLException ex) {
close(stmt);    // close the statement
release(connection);    // release connection
throw new RuntimeException("An sql exception occurred.", ex);    
} finally {
close(stmt); // close the statement
release(connection); // release connection
}
}


private static void release(Connection conn) {
try {
if (conn != null) {
conn.close();
}
} catch (SQLException e) {
e.printStackTrace();
}
}


private static void close(Statement statement) {
try {
if (statement != null) {
statement.close();
}
} catch (SQLException e) {
e.printStackTrace();
}
}
}