package com.dlab.bean;

    public class JdbcBean {

        private String userName;

        private String password;

        private String Url;

        private String jdbcDriverName;

        public String getUserName() {

            return userName;

        }

        public void setUserName(String userName) {

            this.userName = userName;

        }

        public String getPassword() {

            return password;

        }

        public void setPassword(String password) {

            this.password = password;

        }

        public String getUrl() {

            return Url;

        }

        public void setUrl(String url) {

            Url = url;

        }

        public String getJdbcDriverName() {

            return jdbcDriverName;

        }

        public void setJdbcDriverName(String jdbcDriverName) {

            this.jdbcDriverName = jdbcDriverName;

        }

    }

package com.dlab.util;

    import java.io.IOException;

    import java.io.InputStream;

    import java.util.Properties;

    import com.dlab.bean.JdbcBean;

    public class JdbcConfig {

        private JdbcBean jdbcBean;

        public JdbcConfig()  throws IOException{

                //使用InputStream读取配置文件

                InputStream in = Thread.currentThread().getContextClassLoader().getResourceAsStream("config.properties");

                Properties configReader = new Properties();

                //加载配置文件

                configReader.load(in);

                jdbcBean = new JdbcBean();

                jdbcBean.setUserName(configReader.getProperty("username"));

                jdbcBean.setPassword(configReader.getProperty("password"));

                jdbcBean.setUrl(configReader.getProperty("url"));

                jdbcBean.setJdbcDriverName(configReader.getProperty("jdbcDriverName"));

        }

        //返回JdbcBean对象

        public JdbcBean getConfigInfo(){

            return jdbcBean;

        }

    }

package com.dlab.util;

    import java.io.IOException;

    import java.sql.Connection;

    import java.sql.DriverManager;

    import java.sql.PreparedStatement;

    import java.sql.ResultSet;

    import java.sql.SQLException;

    import com.dlab.bean.JdbcBean;

    public class DBUtil {

        /**

         * 采用单例模式

         */

        private static DBUtil instance = new DBUtil();

        private Connection conn;

        private DBUtil (){

            JdbcBean jdbcBean;

            try {

                jdbcBean = new JdbcConfig().getConfigInfo();

                Class.forName(jdbcBean.getJdbcDriverName());

                conn = DriverManager.getConnection(jdbcBean.getUrl(), jdbcBean.getUserName(), jdbcBean.getPassword());

            } catch (IOException e) {

                e.printStackTrace();

            } catch (ClassNotFoundException e) {

                e.printStackTrace();

            } catch (SQLException e) {

                e.printStackTrace();

            }

        }

        public static synchronized DBUtil getInstance (){

            return instance;

        }

        //返回Connection

        public Connection getConn(){

            return conn;

        }

        //Connection的静态关闭方法

        public static void close(Connection conn){

            if(conn != null){

                try {

                    conn.close();

                } catch (SQLException e) {

                    e.printStackTrace();

                }

            }

        }

        //PreparedStatement的静态关闭方法

        public static void close(PreparedStatement pstmt){

            if(pstmt != null){

                try {

                    pstmt.close();

                } catch (SQLException e) {

                    e.printStackTrace();

                }

            }

        }

        //ResultSet的静态关闭方法

        public static void close(ResultSet rs){

            if(rs != null){

                try {

                    rs.close();

                } catch (SQLException e) {

                    e.printStackTrace();

                }

            }

        }

    }

package com.dlab.dbtest;

    import java.sql.Connection;

    import java.sql.PreparedStatement;

    import java.sql.ResultSet;

    import java.sql.SQLException;

    import com.dlab.util.DBUtil;

    public class DBTest {

        public static void main(String[] args) {

            String sql = "select * from Admin";

            Connection conn = null;

            PreparedStatement pstmt = null;

            ResultSet rs = null;

            try {

                conn = DBUtil.getInstance().getConn();

                pstmt = conn.prepareStatement(sql);

                rs = pstmt.executeQuery();

                while(rs.next()){

                    System.out.println(rs.getString("Admin_Username"));

                }

            } catch (SQLException e) {

                e.printStackTrace();

            } finally {

                DBUtil.close(rs);

                DBUtil.close(pstmt);

                DBUtil.close(conn);

            }

        }

    }