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());
         }
     }
 }