繼續我們的冒險體驗，之前綜述了一些構建一個專案的大致流程，相信大家對於系統的框架已經瞭然於胸。 今天我們就來談一談，如何構建資料的橋樑。

這裡我們使用commons-dbutils 來簡單的封裝一個jdbc template, 幫助我們實現快速的CRUD. 廢話不多講直接上程式碼。

package org.foothold.learn2.helper;

import org.apache.commons.dbcp2.BasicDataSource;
import org.apache.commons.dbutils.QueryRunner;
import org.apache.commons.dbutils.handlers.BeanHandler;
import org.apache.commons.dbutils.handlers.BeanListHandler;
import org.apache.commons.dbutils.handlers.MapListHandler;
import org.foothold.learn2.util.PropsUtil;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;

import java.sql.Connection;
import java.sql.DriverManager;
import java.sql.SQLException;
import java.util.ArrayList;
import java.util.List;
import java.util.Map;
import java.util.Properties;

/**
 * Created by Jaden.Gu on 2018/11/16.
 */
public class DatabaseHelper {
    private static final Logger logger = LoggerFactory.getLogger(DatabaseHelper.class);
    private static final QueryRunner QUERY_RUNNER = new QueryRunner();

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

    private static final BasicDataSource basicDataSource;

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

    static {
        Properties properties = PropsUtil.loadProps("db.properties");
        basicDataSource = new BasicDataSource();

        DRIVER = properties.getProperty("jdbc.driver");
        URL = properties.getProperty("jdbc.url");
        USERNAME = properties.getProperty("jdbc.username");
        PASSWORD = properties.getProperty("jdbc.password");

        basicDataSource.setDriverClassName(DRIVER);
        basicDataSource.setUrl(URL);
        basicDataSource.setUsername(USERNAME);
        basicDataSource.setPassword(PASSWORD);

//        try {
//            Class.forName(DRIVER);
//        } catch (ClassNotFoundException ex) {
//            logger.error("DatabaseHelper ClassNotFoundException", ex);
//        }
    }

    public static Connection getConnection() {
        Connection conn = null;

        try {
            if(CONNECTION_HOLDER.get() == null) {
//                conn = DriverManager.getConnection(URL, USERNAME, PASSWORD);
                conn = basicDataSource.getConnection();
                CONNECTION_HOLDER.set(conn);
            }

        } catch (SQLException ex) {
            logger.error("getConnection", ex);
        }

        return  CONNECTION_HOLDER.get();
    }

    public static void closeConnection() {
        if(CONNECTION_HOLDER.get() != null) {
            try {
                CONNECTION_HOLDER.get().close();
            } catch (SQLException ex) {
                logger.error("closeConnection", ex);
            }
        }
    }

    public static <T> List<T> queryEntityList(Class<T> entityClass, String sql, Object... params) {
        List<T> entityList = null;

        try {
            entityList = QUERY_RUNNER.query(getConnection(), sql, new BeanListHandler<T>(entityClass), params);
        }catch (SQLException ex) {
            logger.error("query entity list failure", ex);
            throw new RuntimeException(ex);
        } finally {
            closeConnection();
        }

        return entityList;
    }

    public static <T> T queryEntity(Class<T> entityClass, String sql, Object... params) {
        T entity = null;

        try {
            Connection connection = getConnection();

            entity = QUERY_RUNNER.query(connection, sql, new BeanHandler<T>(entityClass), params);
        } catch (SQLException ex) {
            logger.error("queryEntity sql exception", ex);
            throw new RuntimeException(ex);
        } finally {
            closeConnection();
        }

        return  entity;
    }

    public static List<Map<String, Object>> executeQuery(String sql, Object... params) {
        List<Map<String, Object>> result = null;

        try{
            Connection conn = getConnection();

            result = QUERY_RUNNER.query(conn, sql, new MapListHandler(), params);
        } catch (SQLException ex) {
            logger.error("executeQuery sql exception", ex);
            throw new RuntimeException(ex);
        } finally {
            closeConnection();
        }

        return result;
    }

    public static int executeUpdate(String sql, Object... params) {
        int rows = 0;

        try{
            rows = QUERY_RUNNER.update(getConnection(), sql, params);

        } catch (SQLException ex) {
            logger.error("executeUpdate sql exception", ex);
            throw new RuntimeException(ex);
        } finally {
            closeConnection();
        }

        return rows;
    }

    public static <T> boolean insertEntity(Class<T> entityClass, Map<String, Object> fieldMap) {
        if(fieldMap.isEmpty()) {
            logger.error("Can't insert entity : field is empty");
            return false;
        }

        String sql = String.format("INSERT INTO %s", getTableName(entityClass));

        StringBuilder columns = new StringBuilder("(");
        StringBuilder values = new StringBuilder("(");

        for(String column : fieldMap.keySet()) {
            columns.append(column).append(", ");
            values.append("?, ");
        }

        columns.replace(columns.lastIndexOf(", "), columns.length(), ")");
        values.replace(values.lastIndexOf(", "), values.length(), ")");
        sql += columns + " VALUES " + values;

        Object[] parmas = fieldMap.values().toArray();

        return executeUpdate(sql, parmas) == 1;
    }

    public static <T> boolean updateEntity(Class<T> entityClass, Map<String, Object> fieldMap, long id) {

        if(fieldMap.isEmpty()) {
            logger.error("Can't update entity : field is empty");
            return false;
        }

        String sql = "UPDATE " + getTableName(entityClass) + " SET ";

        StringBuilder columns = new StringBuilder();

        for(String column : fieldMap.keySet()) {
            columns.append(String.format(" %s = ? ", column));
        }

        sql += columns.substring(0, columns.length() -1) + " WHERE id = ? ";

        List<Object> paramList = new ArrayList<>();

        paramList.addAll(fieldMap.values());

        paramList.add(id);

        Object[] params = paramList.toArray();

        return  executeUpdate(sql, params) == 1;
    }

    public static <T> boolean deleteEntity(Class<T> entityClass, long id) {
        String sql = "DELETE FROM " + getTableName(entityClass) + " WHERE id = ?";
        return executeUpdate(sql, id) == 1;
    }

    private static String getTableName(Class<?> entityClass) {
        return entityClass.getSimpleName().toLowerCase();
    }

}

 

在static 程式碼快裡，我們讀取了配置檔案，然後通過配置的資料庫驅動類，資料庫使用者名稱、密碼。初始化一個dpcp2 的資料來源，然後通過dpcp2資料庫連線池管理資料庫連線，這樣有助於減少頻繁建立資料庫所帶來的昂貴開銷。另外我們把從連線池中取到的連線放到了ThreadLocal中，實現了統一請求的連線複用。

若要使用dpcp2我們需要在pom.xml裡新增以下依賴：

   <dependency>
          <groupId>org.apache.commons</groupId>
          <artifactId>commons-dbcp2</artifactId>
          <version>2.1.1</version>
   </dependency>

 

若想了解資料庫連線池可以點選下方連結：
https://www.cnblogs.com/aspirant/p/6747238.html