一、ORM对象关系映射

• 数据库中的一个表：Java中的一个类
• 数据库中的一个字段：Java中的一个属性
• 数据表中的一条数据：Java中的一个对象

二、表结构和表对应的实体类

CREATE TABLE `databaseInfo` (
  `id` int(11) NOT NULL AUTO_INCREMENT COMMENT '自增id',
  `database_name` varchar(100) NOT NULL COMMENT '数据库名称',
  `table_name` varchar(100) NOT NULL COMMENT '表名',
  `table_comment` varchar(300) DEFAULT NULL COMMENT '表的描述',
  `table_rows` bigint(20) DEFAULT 0 COMMENT '表的行数',
  `table_key` varchar(100) NOT NULL COMMENT '表的主键',
  `create_time` datetime DEFAULT NULL COMMENT '创建时间',
  `update_time` datetime DEFAULT NULL COMMENT '更新时间',
  PRIMARY KEY (`id`),
  UNIQUE KEY `uniq_databasename_tablename` (`database_name`,`table_name`)
) ENGINE=InnoDB AUTO_INCREMENT=1 DEFAULT CHARSET=utf8mb4 COMMENT='源数据库表信息';

import lombok.AllArgsConstructor;
import lombok.Data;
import lombok.EqualsAndHashCode;
import lombok.ToString;

import java.io.Serializable;

/**
 * 数据库元信息
 */
@Data
@AllArgsConstructor
@EqualsAndHashCode(callSuper = false)
@ToString
public class DatabaseInfo implements Serializable {

    /**
     * 数据库名称
     */
    private String databaseName;

    /**
     * 数据表全称,格式：dbName.tableName
     */
    private String tableName;

    /**
     * 表的描述
     */
    private String tableComment;

    /**
     * 表的行数
     */
    private Long tableRows;

    /**
     * 表的主键
     */
    private String tableKey;
}

三、查询mysql数据库元信息ORM映射到实体类中

    public DatabaseInfo get() throws SQLException, IOException, ClassNotFoundException {

        DatabaseInfo databaseInfo = null;
        Connection conn = null;
        PreparedStatement ps = null;
        ResultSet rs = null;

        try {
            //1.获取连接

            conn = JdbcUtils.getConnection();
            //2.获取PreparedStatement，用于发送sql
            String sql = "select t.TABLE_SCHEMA as DATABASE_NAME,CONCAT_WS('.',t.TABLE_SCHEMA,t" +
                    ".TABLE_NAME) as TABLE_NAME,\n" +
                    "t.TABLE_COMMENT,t.TABLE_ROWS,k.COLUMN_NAME as TABLE_KEY \n" +
                    "from INFORMATION_SCHEMA.TABLES as t\n" +
                    "inner join INFORMATION_SCHEMA.KEY_COLUMN_USAGE as k\n" +
                    "on k.TABLE_NAME=t.TABLE_NAME and CONSTRAINT_NAME = 'PRIMARY' and t.TABLE_SCHEMA " +
                    "= ?";
            ps = conn.prepareStatement(sql);

            //3.填充占位符
            ps.setString(1, "dw");

            //4.执行sql,获取ResultSet
            rs = ps.executeQuery();

            //5.获取结果集中的数据
            if (rs.next()) {
                String datbase_name = rs.getString("DATABASE_NAME");
                String table_name = rs.getString("TABLE_NAME");
                String table_comment = rs.getString("TABLE_COMMENT");
                Long table_rows = rs.getLong("TABLE_ROWS");
                String table_key = rs.getString("TABLE_KEY");

                //6.将结果集中获取的散列数据封装进对象
                databaseInfo = new DatabaseInfo(datbase_name, table_name, table_comment, table_rows,
                        table_key);
            }
        }catch (Exception e){
                e.printStackTrace();
            }finally {
            //7.关闭连接
                JdbcUtils.release(conn,ps,rs);
            }
        return databaseInfo;

    }

四、测试类

    @Test
    public void test4() throws SQLException, IOException, ClassNotFoundException {
        DatabaseInfo databaseInfo = get();
        if(databaseInfo == null){
            System.out.println("无法获取数据库元信息");
        }else{
            System.out.println("查询到指定mysql数据库元信息");
            System.out.println(databaseInfo);
        }
    }

五、完整代码

import com.bigdata.plus.Entity.DatabaseInfo;
import org.junit.Test;

import java.io.IOException;
import java.sql.Connection;
import java.sql.PreparedStatement;
import java.sql.ResultSet;
import java.sql.SQLException;
import java.util.ArrayList;
import java.util.Date;
import java.util.Iterator;
import java.util.List;

/*
    使用PrepareStatement完成增删改
*/
public class PrepareStatementTest {

    @Test
    public void test4() throws SQLException, IOException, ClassNotFoundException {
        DatabaseInfo databaseInfo = get();
        if(databaseInfo == null){
            System.out.println("无法获取数据库元信息");
        }else{
            System.out.println("查询到指定mysql数据库元信息");
            System.out.println(databaseInfo);
        }
    }

    public DatabaseInfo get() throws SQLException, IOException, ClassNotFoundException {

        DatabaseInfo databaseInfo = null;
        Connection conn = null;
        PreparedStatement ps = null;
        ResultSet rs = null;

        try {
            //1.获取连接

            conn = JdbcUtils.getConnection();
            //2.获取PreparedStatement，用于发送sql
            String sql = "select t.TABLE_SCHEMA as DATABASE_NAME,CONCAT_WS('.',t.TABLE_SCHEMA,t" +
                    ".TABLE_NAME) as TABLE_NAME,\n" +
                    "t.TABLE_COMMENT,t.TABLE_ROWS,k.COLUMN_NAME as TABLE_KEY \n" +
                    "from INFORMATION_SCHEMA.TABLES as t\n" +
                    "inner join INFORMATION_SCHEMA.KEY_COLUMN_USAGE as k\n" +
                    "on k.TABLE_NAME=t.TABLE_NAME and CONSTRAINT_NAME = 'PRIMARY' and t.TABLE_SCHEMA " +
                    "= ?";
            ps = conn.prepareStatement(sql);

            //3.填充占位符
            ps.setString(1, "dw");

            //4.执行sql,获取ResultSet
            rs = ps.executeQuery();

            //5.获取结果集中的数据
            if (rs.next()) {
                String datbase_name = rs.getString("DATABASE_NAME");
                String table_name = rs.getString("TABLE_NAME");
                String table_comment = rs.getString("TABLE_COMMENT");
                Long table_rows = rs.getLong("TABLE_ROWS");
                String table_key = rs.getString("TABLE_KEY");

                //6.将结果集中获取的散列数据封装进对象
                databaseInfo = new DatabaseInfo(datbase_name, table_name, table_comment, table_rows,
                        table_key);
            }
        }catch (Exception e){
                e.printStackTrace();
            }finally {
            //7.关闭连接
                JdbcUtils.release(conn,ps,rs);
            }
        return databaseInfo;

    }
}

六、运行测试类输出如下所示