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DBUtil工具类

作者:互联网

DBUtil工具类

IRowMapper接口

import java.sql.ResultSet;

@FunctionalInterface
public interface IRowMapper{
void mapRow(ResultSet resultSet);
}

DBUtil类

import java.sql.*;

/**
 * @author venking
 */
public class DBUtil {


    static {
        try {
            Class.forName("com.mysql.jdbc.Driver");
        } catch (ClassNotFoundException e) {
            e.printStackTrace();
        }
    }
    private DBUtil() { }

    /**
     * 执行SQL查询,返回一个ResultSet对象,使用完毕后记得调用closeAll方法关闭资源
     * @param sql SQL语句
     * @return 根据SQL语句查询到的ResultSet
     */
    public static ResultSet select(String sql){
        try{
            Connection connection = getConnection();
            Statement statement = connection.createStatement();
            return statement.executeQuery(sql);
        } catch (SQLException e) {
            e.printStackTrace();
        }
        return null;
    }

    /**
     * 以回调的方式查询并处理数据
     * @param sql SQL语句
     * @param rowMapper 处理数据的对象
     */
    public static void select(String sql,IRowMapper rowMapper){
        try(
                Connection connection = getConnection();
                Statement statement = connection.createStatement();
                ResultSet resultSet = statement.executeQuery(sql)
        ){
            rowMapper.mapRow(resultSet);
        } catch (SQLException e) {
            e.printStackTrace();
        }
    }

    /**
     * 以预处理的方式,查询结果,并返回包含查询结果的ResultSet,使用完Result之后记得调用closeAll()关闭资源
     * @param sql 要查询的SQL语句
     * @param objects 要传入的参数
     * @return 返回一个包含查询数据的ResultSet
     */
    public static ResultSet preparedSelect(String sql,Object...objects){
        try {
            Connection connection = getConnection();
            PreparedStatement preparedStatement = connection.prepareStatement(sql);
            for (int i = 0; i < objects.length; i++) {
                preparedStatement.setObject(i+1,objects[i]);
            }
            return preparedStatement.executeQuery();
        } catch (SQLException throwables) {
            throwables.printStackTrace();
        }
        return null;
    }

    /**
     * 使用PreparedStatement查询并使用RowMapper处理数据
     * @param sql SQL语句
     * @param rowMapper 回调接口IRowMapper的实现对象
     * @param objects PrepareStatement参数列表
     */
    public static void preparedSelect(String sql, IRowMapper rowMapper,Object...objects){
        ResultSet resultSet = preparedSelect(sql,objects);
        rowMapper.mapRow(resultSet);
        closeAll(resultSet);
    }

    /**
     * 判断用户名是否存在
     * @param userName 要判断的用户名
     * @return 存在返回true,否则返回false
     */
    public static boolean exists(String userName){
        return exists("user_name",userName);
    }


    /**
     * 判断指定列名里面是包含有指定的值
     * @param columnName    列名
     * @param value 值
     * @return  如果有,返回true,否则返回false,异常时会返回true
     */
    public static boolean exists(String columnName,String value){
        String sql = "select id from user_info where " + columnName + " = '" + value + "'";
        ResultSet resultSet = select(sql);
        try {
                return resultSet != null && resultSet.next();
        } catch (SQLException throwables) {
            throwables.printStackTrace();
        }finally {
            closeAll(resultSet);
        }
        return false;
    }

    /**
     * 采用防止SQL注入的方式,判断用户名是否存在,存在返回true,否则返回false
     * @param userName 要判断的用户名
     * @return 存在返回true,否则返回false
     */
    public static boolean preparedExists(String userName){
        return preparedExists("user_name",userName);
    }

    /**
     * 采用防止SQL注入的方式,判断指定列名里面是包含有指定的值
     * @param columnName    列名
     * @param value 值
     * @return  如果有,返回true,否则返回false
     */
    public static boolean preparedExists(String columnName, String value){
        String sql = "select id from user_info where +" + columnName +"= ?";
        ResultSet resultSet = preparedSelect(sql,value);
        try {
            return resultSet != null && resultSet.next();
        } catch (SQLException throwables) {
            throwables.printStackTrace();
        }finally {
            closeAll(resultSet);
        }
        return false;
    }

    /**
     * 获取数据库连接
     * @return Connection对象
     * @throws SQLException 获取连接时可能会发生错误,抛出一个检查时异常SQLException
     */
    public static  Connection getConnection() throws SQLException {
        String url = PropertiesUtil.getValue("url");
        String user = PropertiesUtil.getValue("user");
        String password = PropertiesUtil.getValue("password");
        return DriverManager.getConnection(url,user,password);
    }

    /**
     * 执行DML语句,根据受影响的行数返回true或者false
     * @param sql SQL语句
     * @return 受影响的行数 > 0 返回true,否则返回false
     */
    public static boolean update(String sql){
        try (
            Connection connection = getConnection();
            Statement statement = connection.createStatement()
            ){
        int effect = statement.executeUpdate(sql);
        return effect > 0;
        } catch (SQLException throwable) {
            throwable.printStackTrace();
        }
        return false;
    }

    /**
     * 以PreparedStatement的方式执行DML语句,并根据受影响的行数返回true或者false
     * @param sql SQL语句
     * @param objects PrepareStatement中的参数
     * @return 受影响的行数 > 0 返回true,否则返回false
     */
    public static boolean preparedUpdate(String sql,Object...objects){
        try (
                Connection connection = getConnection();
                PreparedStatement preparedStatement = connection.prepareStatement(sql)
        ){
            for (int i = 0; i < objects.length; i++) {
                preparedStatement.setObject(i + 1, objects[i]);
            }
            int effect = preparedStatement.executeUpdate();
            return effect > 0;
        } catch (SQLException throwable) {
            throwable.printStackTrace();
        }
        return false;
    }

    public static boolean isEmpty(ResultSet resultSet){
        try {
            return resultSet != null && resultSet.next();
        } catch (SQLException throwables) {
            throwables.printStackTrace();
        }finally {
            closeAll(resultSet);
        }
        return false;
    }
    /**
     * 根据传入的ResultSet获取Statement和Connection,关闭这三个资源
     */
    public static void closeAll(ResultSet resultSet){
        try {
            close(resultSet, resultSet.getStatement(), resultSet.getStatement().getConnection());
        } catch (SQLException throwables) {
            throwables.printStackTrace();
        }
    }

    /**
     * 关闭ResultSet资源
     * @param resultSet 要关闭的ResultSet
     */
    private static void close(ResultSet resultSet){
        if (resultSet != null){
            try {
                resultSet.close();
            } catch (SQLException throwables) {
                throwables.printStackTrace();
            }
        }
    }
    private static void close(Statement statement, Connection connection){
        if(statement != null){
            try {
                statement.close();
            } catch (SQLException throwables) {
                throwables.printStackTrace();
            }
        }
        if(connection != null){
            try {
                connection.close();
            } catch (SQLException throwables) {
                throwables.printStackTrace();
            }
        }
    }
    private static void close(ResultSet resultSet,Statement statement, Connection connection){
        close(resultSet);
        close(statement,connection);
    }



    public static void main(String[] args) {
        System.out.println(DBUtil.preparedExists("admin"));
        System.out.println(DBUtil.exists("admin"));
    }
}

标签:return,ResultSet,resultSet,param,static,sql,工具,DBUtil
来源: https://blog.csdn.net/m0_56506584/article/details/117571791