借助Java的JDBC自制“DBMS”管理操作数据库

package jdbc;

import java.sql.Connection;
import java.sql.Driver;
import java.sql.DriverManager;
import java.sql.ResultSetMetaData;

/**
 * @author liuwenlong
 * @create 2020-08-11 14:36:20
 */
@SuppressWarnings("all")
public class LwlSql {
    public static void main(String[] args) {
        Connection conn = null;
        try {
            //第一步，测试是否已经添加了操作oracle的jar包
            Class.forName("oracle.jdbc.driver.OracleDriver");
            //第二步：和数据库连接
            conn = DriverManager.getConnection("jdbc:oracle:thin:@192.168.1.3:1521:xe", "lwl", "123456");
            //第三步，创建执行sql语句的对象
            java.sql.Statement st = conn.createStatement();

            java.sql.ResultSet rs = null;
            byte[] b = new byte[300];
            String sql = null;
            while (true) {
                try {
                    System.out.println("jwlSql>");
                    int len = System.in.read(b);
                    if (len < 5) {
                        System.err.println("invalid sql");
                        continue;
                    }
                    if (b[len - 2] == 13 && b[len - 1] == 10) {
                        len = len - 2;
                    } else {
                        len = len - 1;
                    }
                    sql = new String(b, 0, len);
                    if (sql.equals("exit") || sql.equals("quit")) {
                        System.out.println("welcome again!!");
                        return;
                    }
                    //查询
                    if (sql.startsWith("select")) {
                        rs = st.executeQuery(sql);
                        ResultSetMetaData md = rs.getMetaData();
                        int fld = md.getColumnCount();
                        for (int i = 1; i <= fld; i++) {
                            System.out.print(md.getColumnName(i) + "\t");//显示列名字
                        }
                        System.out.println();
                        while (rs.next()) {//显示数据
                            for (int i = 1; i <= fld; i++) {
                                System.out.print(rs.getString(i) + "\t\t");
                            }
                            System.out.println();
                        }
                    } else {
                        st.executeUpdate(sql);
                    }
                } catch (Exception e) {
                    System.err.println(e.getMessage());
                }
            }
        } catch (Exception e) {
            System.err.println(e.getMessage());
        }
    }
}