JAVA WEB中如何让数据库连接对开发人员完全透明？

package org.smart4j.chapter2.util;

import java.io.FileNotFoundException;
import java.io.IOException;
import java.io.InputStream;
import java.util.Properties;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;

/**
 * Created by sahara on 2016/3/15.
 */
public final class PropsUtil {
    private static final Logger LOGGER=LoggerFactory.getLogger(PropsUtil.class);

    public static Properties loadProps(String fileName){
        Properties props = null;
        InputStream is = null;
        try {
            is = Thread.currentThread().getContextClassLoader().getResourceAsStream(fileName);
            if (is == null) {
                throw new FileNotFoundException(fileName + "file is not found");
            }
            props = new Properties();
            props.load(is);
        } catch (IOException e){
            LOGGER.error("load propertis file failure", e);
        } finally {
            if (is != null) {
                try {
                    is.close();
                } catch (IOException e) {
                    LOGGER.error("close input stream failure", e);
                }
            }
        }
        return props;
    }

    public static String getString(Properties props, String key) {
        return getString(props, key, "");
    }

    public static String getString(Properties props, String key, String defaultValue) {
        String value = defaultValue;
        if (props.containsKey(key)) {
            value = props.getProperty(key);
        }
        return value;
    }

    public static int getInt(Properties props, String key) {
        return getInt(props, key, 0);
    }

    public static int getInt(Properties props, String key , int defaultValue) {
        int value = defaultValue;
        if (props.containsKey(key)) {
            value = CastUtil.castInt(props.getProperty(key));
        }
        return value;
    }
    public static boolean getBoolean(Properties props, String key) {
        return getBoolean(props, key, false);
    }

    public static boolean getBoolean(Properties props, String key, Boolean defaultValue) {
        boolean value = defaultValue;
        if (props.containsKey(key)) {
            value = CastUtil.castBoolean(props.getProperty(key));
        }
        return value;
    }
}

package org.smart4j.chapter2.model;

/**
 * Created by sahara on 2016/3/14.
 */
public class Customer {
    private long id;
    private String name;
    private String contact;
    private String telephone;
    private String email;
    private String remark;

    public long getId() {
        return id;
    }

    public void setId(long id) {
        this.id = id;
    }

    public String getRemark() {
        return remark;
    }

    public void setRemark(String remark) {
        this.remark = remark;
    }

    public String getEmail() {
        return email;
    }

    public void setEmail(String email) {
        this.email = email;
    }

    public String getTelephone() {
        return telephone;
    }

    public void setTelephone(String telephone) {
        this.telephone = telephone;
    }

    public String getContact() {
        return contact;
    }

    public void setContact(String contact) {
        this.contact = contact;
    }

    public String getName() {
        return name;
    }

    public void setName(String name) {
        this.name = name;
    }
}

package org.smart4j.chapter2.helper;

import java.sql.Connection;
import java.sql.DriverManager;
import java.sql.SQLException;
import java.util.List;
import java.util.Properties;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;
import org.apache.commons.dbutils.QueryRunner;
import org.apache.commons.dbutils.handlers.BeanListHandler;
import org.smart4j.chapter2.util.PropsUtil;

/**
 * Created by sahara on 2016/3/16.
 */
public final class DatabaseHelper {
    private static final Logger LOGGER = LoggerFactory.getLogger((DatabaseHelper.class));

    private static final String DRIVER;
    private static final String URL;
    private static final String USERNAME;
    private static final String PASSWORD;

    private static final QueryRunner QUERY_RUNNER = new QueryRunner();
    private static final ThreadLocal<Connection> CONNECTION_HOLDER = new ThreadLocal<Connection>();

    static  {
        Properties conf = PropsUtil.loadProps("config.properties");
        DRIVER = conf.getProperty("jdbc.driver");
        URL = conf.getProperty("jdbc.url");
        USERNAME = conf.getProperty("jdbc.username");
        PASSWORD = conf.getProperty("jdbc.password");


        try {
            Class.forName(DRIVER);
        } catch (ClassNotFoundException e) {
            LOGGER.error("can not load jdbc driver", e);
        }
    }

    public static Connection getConnection() {
        Connection conn = CONNECTION_HOLDER.get();
        if (conn == null) {
            try {
                conn = DriverManager.getConnection(URL, USERNAME, PASSWORD);
            }catch (SQLException e) {
                LOGGER.error("get connection failure", e);
                throw new RuntimeException(e);
            }finally {
                CONNECTION_HOLDER.set(conn);
            }
        }
        return conn;
    }

    public static void closeConnection() {
        Connection conn =CONNECTION_HOLDER.get();
        if (conn != null) {
            try {
                conn.close();
            } catch (SQLException e) {
                LOGGER.error("close connection failure", e);
                throw new RuntimeException(e);
            }finally {
                CONNECTION_HOLDER.remove();
            }
        }
    }

    public static <T> List<T> queryEntityList(Class<T> entityClass, String sql, Object...params) {
        List<T> entityList;
        try {
            Connection conn = getConnection();
            entityList = QUERY_RUNNER.query(conn, sql, new BeanListHandler<T>(entityClass), params);
        } catch (SQLException e) {
            LOGGER.error("query entity list failure", e);
            throw new RuntimeException(e);
        } finally {
            closeConnection();
        }
        return entityList;
    }
}

package org.smart4j.chapter2.service;

import java.sql.*;
import java.util.ArrayList;
import java.util.List;
import java.util.Map;
import java.util.Properties;


import org.omg.PortableInterceptor.USER_EXCEPTION;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;
import org.smart4j.chapter2.model.Customer;
import org.smart4j.chapter2.util.PropsUtil;
import org.smart4j.chapter2.helper.DatabaseHelper;

/**
 * Created by sahara on 2016/3/14.
 */
public class CustomerService {
    private static final Logger LOGGER = LoggerFactory.getLogger((CustomerService.class));

    public List<Customer> getCustomerList() {
        String sql = "SELECT * FROM customer";
        return DatabaseHelper.queryEntityList(Customer.class, sql);
    }

    public Customer getCustomer(long id) {
        // TODO
        return null;
    }

    public boolean createCustomer(Map<String, Object> fieldMap) {
        // TODO
        return false;
    }

    public boolean updateCustomer(long id, Map<String, Object> fieldMap) {
        // TODO
        return false;
    }
}