瞎j8封装第二版之数据层的封装

Posted 2020-10-19 yeyeck

 

看了以前写的代码，对就是下面这个

    手把手封装数据层之DataUtil数据库操作的封装

觉得以前写的代码好烂啊！！！，重新理了一下思路，写得更规范和简练，应该效率也会高很多，用了一下下午写的连接池（半废品。。。）

瞎j8封装第二版之数据库连接池

 

下面直接上代码，代码很好理解，就是用了简单的反射，注解的部分我都写了注释

package jdbc;

import util.StringUtil;

import java.lang.reflect.Field;
import java.lang.reflect.InvocationTargetException;
import java.lang.reflect.Method;
import java.sql.*;
import java.util.ArrayList;
import java.util.List;

public class DataUtil {


    public static int excuteUpdate(String sql, Object... objects) {
        Connection connection = ConnectionPool.getInstance().getCurrentConnection();
        PreparedStatement preparedStatement = null;
        try {
            preparedStatement = getStateMent(connection, sql, objects);
            return preparedStatement.executeUpdate(); //执行sql并返回结果
        } catch (SQLException e) {
            e.printStackTrace();
        } finally {
            if (preparedStatement != null) {
                try {
                    preparedStatement.close();
                } catch (SQLException e) {
                    e.printStackTrace();
                }
            }

        }
        return 0;
    }


    /**
     * 查询单挑记录
     *
     * @param sql  查询语句
     * @param clazz 返回对象的class
     * @param objects 需要的参数，必须跟sql占位符的位置一一对应
     * @param <T>   泛型返回
     * @return      返回单个对象
     */
    public static <T> T queryForObject(String sql, Class<T> clazz, Object... objects) {
        Connection connection = ConnectionPool.getInstance().getCurrentConnection();
        PreparedStatement preparedStatement = null;
        ResultSet resultSet = null;
        T object = null;
        try {
            preparedStatement = getStateMent(connection, sql, objects);
            resultSet = getResultSet(preparedStatement);
            if (resultSet.next()) {
                object = invokeObject(resultSet, clazz);
            }

        } catch (SQLException e) {
            e.printStackTrace();
        } catch (IllegalAccessException e) {
            e.printStackTrace();
        } catch (InstantiationException e) {
            e.printStackTrace();
        } catch (NoSuchFieldException e) {
            e.printStackTrace();
        } catch (NoSuchMethodException e) {
            e.printStackTrace();
        } catch (InvocationTargetException e) {
            e.printStackTrace();
        } finally {
            close(preparedStatement, resultSet); //记得关闭
        }
        return object;
    }

    /**
     *查询多条记录
     *
     * @param sql  查询语句
     * @param clazz 返回对象的class
     * @param objects 需要的参数，必须跟sql占位符的位置一一对应
     * @param <T>   泛型返回
     *
     * @return list
     */
    public static <T> List<T> queryForList(String sql, Class<T> clazz, Object... objects) {
        Connection connection = ConnectionPool.getInstance().getCurrentConnection();
        PreparedStatement preparedStatement = null;
        ResultSet resultSet = null;
        List<T> list = new ArrayList<T>();
        try {
            preparedStatement = getStateMent(connection, sql, objects);
            resultSet = getResultSet(preparedStatement);
            while (resultSet.next()) {
                list.add(invokeObject(resultSet, clazz));
            }
        } catch (SQLException e) {
            e.printStackTrace();
        } catch (IllegalAccessException e) {
            e.printStackTrace();
        } catch (InstantiationException e) {
            e.printStackTrace();
        } catch (InvocationTargetException e) {
            e.printStackTrace();
        } catch (NoSuchMethodException e) {
            e.printStackTrace();
        } catch (NoSuchFieldException e) {
            e.printStackTrace();
        } finally {
            close(preparedStatement, resultSet);
        }

        return list.size() > 0 ? list : null;

    }


    private static void close(PreparedStatement preparedStatement, ResultSet resultSet) {
        try {
            if (preparedStatement != null) {
                preparedStatement.close();
                resultSet.close();
            }
        } catch (SQLException e) {
            e.printStackTrace();
        }
    }

    private static <T> T invokeObject(ResultSet resultSet, Class<T> clazz) throws IllegalAccessException, InstantiationException,
            SQLException, NoSuchFieldException, NoSuchMethodException, InvocationTargetException {
        T object = clazz.newInstance();
        ResultSetMetaData metaData = resultSet.getMetaData();
        for (int i = 0, count = metaData.getColumnCount(); i < count; i++) {
            String columnName = metaData.getColumnName(i + 1);     //数据库返回结果的列名
            String fieldName = StringUtil.camelName(columnName); //去掉列名中的下划线“_”并转为驼峰命名
            Field field = clazz.getDeclaredField(fieldName);            //根据字段名获取field
            String methName = setMethodName(fieldName);         //拼set方法名
            Class type = field.getType();                       //获取字段类型
            Method setMethod = clazz.getDeclaredMethod(methName, field.getType());
            Object value = resultSet.getObject(i + 1);            //获取字段值
            setMethod.invoke(object, type.cast(value));       //强转并且赋值
        }
        return object;
    }

    private static PreparedStatement getStateMent(Connection connection, String sql, Object... objects) throws SQLException {
        if (connection == null) {
            return null;
        }
        PreparedStatement preparedStatement = connection.prepareStatement(sql);
        for (int i = 0, len = objects.length; i < len; i++) {
            preparedStatement.setObject(i + 1, objects[i]);  //给sql每个？占位符填上数据
        }
        return preparedStatement;
    }

    private static ResultSet getResultSet(PreparedStatement statement) throws SQLException {
        if (statement == null) {
            return null;
        } else {
            return statement.executeQuery();
        }
    }

    private static String setMethodName(String str) {
        return "set" + StringUtil.firstUpperCase(str);
    }

}

用到了几个简单的字符串处理方法

package util;

public class StringUtil {

    /**
     * 转为驼峰命名
     * @param str
     * @return string
     */
    public static String camelName(String str) {
        if (!isEmpty(str)) {
            StringBuilder stringBuilder = new StringBuilder();
            for (int i = 0, len = str.length(); i < len; i++) {
                if (str.charAt(i) == ‘_‘) {
                    while (str.charAt(i + 1) == ‘_‘) {
                        i++;
                    }
                    stringBuilder.append(("" + str.charAt(++i)).toUpperCase());
                } else {
                    stringBuilder.append(str.charAt(i));
                }
            }
            return stringBuilder.toString();
        }
        return str;
    }

    /**
     * 判断是否为空串
     * 
     * @param str
     * @return
     */
    public static boolean isBlank(String str) {
        if (str != null && str.length() > 0) {
            for (int i = 0, len = str.length(); i < len; i++) {
                if (!Character.isSpaceChar(str.charAt(i))) {
                    return false;
                }
            }
        }
        return true;
    }

    /**
     * 判断是否为空串 ？！！！ 我怎么又写了个一样的方法？！！！
     * @param str
     * @return
     */
    public static boolean isEmpty(String str) {
        return str == null || str.length() == 0;
    }


    /**
     * 将第一个字母替换为大写
     * @param str
     * @return
     */
    public static String firstUpperCase(String str) {
        return str.substring(0, 1).toUpperCase() + str.substring(1, str.length());
    }
    
}

下面开始是测试了

首先数据库

 

然后测试类，跟表结构对应的

package po;

import java.util.Date;

public class User {

    private Integer id;
    private Integer age;
    private String name;
    private Double score;
    private Date createTime;
    private Date updateTime;

   //set、get 方法均省略了，但是这个是必须的
｝

测试代码

import java.util.List;

public class Test {

    public static void main(String[] args) {
        String sql = "select * from t_user";
        List<User> list = DataUtil.queryForList(sql,User.class);
        System.out.println("查询多条记录：" + list);
        System.out.println("******************************************************************");


        sql = "select * from t_user where id = ?";
        User user = DataUtil.queryForObject(sql,User.class,1);
        System.out.println("查询单条记录：" + user);
        System.out.println("******************************************************************");


        sql = "insert into t_user(name,score,create_time,update_time) values(?,?,now(),now())";
        int t = DataUtil.excuteUpdate(sql,"大牛",66.66);
        System.out.println("执行插入操作结果："+t);

    }
}

测试结果

太晚了，先到这了，有空把我的mybatis和ioc容器也瞎j8重写一下

转载请注明出处：

大王让我写代码   00:12:24