JDBC小结

　　老师如是说：有一个规律永远不变，就是量变引起质变，什么时候你吃的盐比我吃的米多，那你就可以教我了……

1.JDBC是一个标准，是J2EE的一部分；讲tcp时就提到了分层思想，jdbc也是分层，即上层只需要和紧挨着的下层通讯，方便扩展。不管开奥拓车还是开奥迪车方向盘都在屁股前边，档都在右边。不过jdbc还需要写select语句等，而hibernate完全实现了数据库底层，而且屏蔽了细小差别；现在的EJB也实现了某些功能。

2.TestJDBC

　　若是连接字符串或者某些方法忘了（但是有些东西不能忘，比如System.out.println），就注明平时用多了Eclipse，若是查查还能知道……

 import java.sql.*;

  public class TestJDBC {

      public static void main(String[] args) {
          ResultSet rs = null;
          Statement stmt = null;
          Connection conn = null;
          /*
           * 一定要加上try catch finally，不要throws
           * 因为若在遍历过程中出问题，那么下面的关闭就一直执行不了
           * 服务器会越来越卡，最后死掉
           */
          try {
              Class.forName("oracle.jdbc.driver.OracleDriver");
              //new oracle.jdbc.driver.OracleDriver();
              conn = DriverManager.getConnection("jdbc:oracle:thin:@192.168.0.1:1521:SXT", 

 "scott", "tiger");
              stmt = conn.createStatement();
              //结果集就像游标，不过不像数据库，第一条没指向第一条，像iterator
              rs = stmt.executeQuery("select * from dept");
              while(rs.next()) {
                  System.out.println(rs.getString("deptno"));
                  //和实际字段类型无关，只要能转换为int就可以
                  System.out.println(rs.getInt("deptno"));
              }
          } catch (ClassNotFoundException e) {
              e.printStackTrace();
              /*
               * 实际上要用log4j把异常记录在日志里
               */
          } catch (SQLException e) {
              e.printStackTrace();
          } finally {
              /*
               * 要把rs，stmt，conn声明在大try外边
               * 否则在这就不认识了
               */
              try {
                  /*
                   * 不加try catch会出错，因为close也会出错.
                   * 如果rs没有初始化，这直接close那么一定会报错
                   */
                  if(rs != null) {
                      rs.close();
                      /*
                       * 查过api后会发现close后会直接设置为null
                       * 方便gc回收
                       * 写下面的是为了展现良好的编程风格
                       */
                      rs = null;
                  }
                  if(stmt != null) {
                      stmt.close();
                      stmt = null;
                  }
                  if(conn != null) {
                      conn.close();
                      conn = null;
                  }
              } catch (IOException e) {
                  e.printStackTrace();
              }
          }
      }

  }

3.JDBC操作DML语句

 import java.sql.Connection;
 import java.sql.DriverManager;
 import java.sql.ResultSet;
 import java.sql.SQLException;
 import java.sql.Statement;

 public class TestDML {

     /*
      * 执行完DML语句后看是否成功
      * 打开window--show view--other--data
      */
     public static void main(String[] args) {
         Statement stmt = null;
         Connection conn = null;
         try {
             Class.forName("com.mysql.jdbc.Driver");
             conn = DriverManager.getConnection("jdbc:mysql:///news", "root", "root");
             stmt = conn.createStatement();
             String sql = "insert into dept2 values (98, 'GAME', 'BJ')";
             stmt.executeUpdate(sql);
         } catch (ClassNotFoundException e) {
             e.printStackTrace();
         } catch (SQLException e) {
             e.printStackTrace();
         } finally {
             try {
                 if(stmt != null) {
                     stmt.close();
                     stmt = null;
                 }
                 if(conn != null) {
                     conn.close();
                     conn = null;
                 }
             } catch (SQLException e) {
                 e.printStackTrace();
             }
         }
     }

 }

 import java.sql.Connection;
 import java.sql.DriverManager;
 import java.sql.ResultSet;
 import java.sql.SQLException;
 import java.sql.Statement;

 public class TestDML2 {

     /*
      * 从命令行输入
      * 右键 进入run configuration，在arguments输入
      */
     public static void main(String[] args) {
         if(args.length != 3) {
             System.out.println("Parameter Error! Please Input Again!");
             System.exit(-1);
         }

         int deptno = 0;

         try {
             deptno = Integer.parseInt(args[0]);
         } catch (NumberFormatException e) {
             System.out.println("Parameter Error! Deptno should be Number Format!");
             System.exit(-1);
         }
         /*
          * 把这些变量名声明在一块
          */
         String dname = args[1];
         String loc = args[2];

         Statement stmt = null;
         Connection conn = null;
         try {
             Class.forName("oracle.jdbc.driver.OracleDriver");
             //new oracle.jdbc.driver.OracleDriver();
             conn = DriverManager.getConnection("jdbc:oracle:thin:@192.168.0.1:1521:SXT", "scott", "tiger");
             stmt = conn.createStatement();
             //注意values后边有个空格
             String sql = "insert into dept2 values (" + deptno + ",'" + dname + "','" + loc + "')";
             System.out.println(sql);
             stmt.executeUpdate(sql);
         } catch (ClassNotFoundException e) {
             e.printStackTrace();
         } catch (SQLException e) {
             e.printStackTrace();
         } finally {
             try {
                 if(stmt != null) {
                     stmt.close();
                     stmt = null;
                 }
                 if(conn != null) {
                     conn.close();
                     conn = null;
                 }
             } catch (SQLException e) {
                 e.printStackTrace();
             }
         }
     }

 }

4.JDBC处理PreparedStatement

 import java.sql.*;

 public class TestPrepStmt {

     public static void main(String[] args) {
         if(args.length != 3) {
             System.out.println("Parameter Error! Please Input Again!");
             System.exit(-1);
         }

         int deptno = 0;

         try {
             deptno = Integer.parseInt(args[0]);
         } catch (NumberFormatException e) {
             System.out.println("Parameter Error! Deptno should be Number Format!");
             System.exit(-1);
         }

         String dname = args[1];
         String loc = args[2];

         PreparedStatement pstmt = null;
         Connection conn = null;
         try {
             Class.forName("oracle.jdbc.driver.OracleDriver");
             //new oracle.jdbc.driver.OracleDriver();
             conn = DriverManager.getConnection("jdbc:oracle:thin:@192.168.0.1:1521:SXT", "scott", "tiger");
             pstmt = conn.prepareStatement("insert into dept2 values (?, ?, ?)");
             pstmt.setInt(1, deptno);
             pstmt.setString(2, dname);
             pstmt.setString(3, loc);
             pstmt.executeUpdate();
         } catch (ClassNotFoundException e) {
             e.printStackTrace();
         } catch (SQLException e) {
             e.printStackTrace();
         } finally {
             try {
                 if(pstmt != null) {
                     pstmt.close();
                     pstmt = null;
                 }
                 if(conn != null) {
                     conn.close();
                     conn = null;
                 }
             } catch (SQLException e) {
                 e.printStackTrace();
             }
         }
     }

 }

5.JDBC处理存储过程

 import java.sql.*;
 public class TestProc {

     //用的比较少
     public static void main(String[] args) throws Exception {

         Class.forName("oracle.jdbc.driver.OracleDriver");
         Connection conn = DriverManager.getConnection("jdbc:oracle:thin:@192.168.0.1:1521:SXT", "scott", "tiger");
         CallableStatement cstmt = conn.prepareCall("{call p(?, ?, ?, ?)}");
         cstmt.registerOutParameter(3, Types.INTEGER);
         cstmt.registerOutParameter(4, Types.INTEGER);
         cstmt.setInt(1, 3);
         cstmt.setInt(2, 4);
         cstmt.setInt(4, 5);
         cstmt.execute();
         System.out.println(cstmt.getInt(3));
         System.out.println(cstmt.getInt(4));
         cstmt.close();
         conn.close();
     }
 }

6.JDBC事务处理

　　比如转账时至少需要两条update语句，需要同时成功。

 import java.sql.*;
 public class TestTransaction {
     public static void main(String[] args) {

         Connection conn = null;
         Statement stmt = null;

         try {
             Class.forName("oracle.jdbc.driver.OracleDriver");
             conn = DriverManager.getConnection("jdbc:oracle:thin:@127.0.0.1:1521:SXT", "scott", "tiger");

             conn.setAutoCommit(false);
             stmt = conn.createStatement();
             stmt.addBatch("insert into dept2 values (51, '500', 'haha')");
             stmt.addBatch("insert into dept2 values (52, '500', 'haha')");
             stmt.addBatch("insert into dept2 values (53, '500', 'haha')");
             stmt.executeBatch();
             conn.commit();
             //恢复现场，就像那时候做坦克时，变换完前景色后，在恢复回来
             conn.setAutoCommit(true);
         } catch (ClassNotFoundException e) {
             e.printStackTrace();
         } catch(SQLException e) {

             e.printStackTrace();

             try {
                 if(conn != null)
                 {
                     conn.rollback();
                     /*
                      * 下面这句要加上因为可能没执行到18行而异常
                      */
                     conn.setAutoCommit(true);
                 }
             } catch (SQLException e1) {
                 e1.printStackTrace();
             }
         }finally {
             try {
                 if(stmt != null)
                     stmt.close();
                 if(conn != null)
                     conn.close();
             } catch (SQLException e) {
                 e.printStackTrace();
             }
         }
     }
 }

7.JDBC处理可滚动结果集　

 import java.sql.*;

 public class TestScroll {
     public static void main(String args[]) {

         try {
             new oracle.jdbc.driver.OracleDriver();
             String url = "jdbc:oracle:thin:@192.168.0.1:1521:SXT";
             Connection conn = DriverManager
                     .getConnection(url, "scott", "tiger");
             Statement stmt = conn.createStatement(
                     //下面是静态变量
                     //对滚动不敏感表示你可以随便滚动
                     ResultSet.TYPE_SCROLL_INSENSITIVE,
                     //表示并发访问时只能读取
                     ResultSet.CONCUR_READ_ONLY);
             ResultSet rs = stmt
                     .executeQuery("select * from emp order by sal");
             rs.next();
             System.out.println(rs.getInt(1));
             rs.last();
             System.out.println(rs.getString(1));
             System.out.println(rs.isLast());
             System.out.println(rs.isAfterLast());
             //当前记录是第几条记录；先定位到最后一条，再调用,返回的值可表示共多少行
             System.out.println(rs.getRow());
             rs.previous();
             System.out.println(rs.getString(1));
             rs.absolute(6);
             System.out.println(rs.getString(1));
             rs.close();
             stmt.close();
             conn.close();
         } catch (SQLException e) {
             e.printStackTrace();
         }
     }
 }

8.JDBC批处理

 import java.sql.*;
 public class TestBatch {

     public static void main(String[] args) throws Exception {
         Class.forName("oracle.jdbc.driver.OracleDriver");
         Connection conn = DriverManager.getConnection("jdbc:oracle:thin:@192.168.0.1:1521:SXT", "scott", "tiger");

         PreparedStatement ps = conn.prepareStatement("insert into dept2 values (?, ?, ?)");
         ps.setInt(1, 61);
         ps.setString(2, "haha");
         ps.setString(3, "bj");
         ps.addBatch();

         ps.setInt(1, 62);
         ps.setString(2, "haha");
         ps.setString(3, "bj");
         ps.addBatch();

         ps.setInt(1, 63);
         ps.setString(2, "haha");
         ps.setString(3, "bj");
         ps.addBatch();

         ps.executeBatch();
         ps.close();

         conn.close();

     }

 }

9.JDBC处理可更新的结果集

　　最传统的方式往往最有效，新方式可能支持的不好。Oracle不支持的，但是MySql支持的。

 import java.sql.*;
 public class TestUpdataRs {
     public static void main(String args[]){

     try{
         new oracle.jdbc.driver.OracleDriver();
         String url="jdbc:oracle:thin:@192.168.0.1:1521:SXT";
         Connection conn=DriverManager.getConnection(url,"scott","tiger");
         Statement stmt=conn.createStatement(ResultSet.TYPE_SCROLL_INSENSITIVE,ResultSet.CONCUR_UPDATABLE);

         ResultSet rs=stmt.executeQuery("select * from emp2");

         rs.next();
         //更新一行数据,在内存里
         rs.updateString("ename","AAAA");
         //更新进入数据库
         rs.updateRow();

         //插入新行
         rs.moveToInsertRow();
         rs.updateInt(1, 9999);
         rs.updateString("ename","AAAA");
         rs.updateInt("mgr", 7839);
         rs.updateDouble("sal", 99.99);
         //更新进入数据库
         rs.insertRow();
         //将光标移动到新建的行
         rs.moveToCurrentRow();

         //删除行
         rs.absolute(5);
         rs.deleteRow();

         //取消更新
         //rs.cancelRowUpdates();

       }catch(SQLException e){
         e.printStackTrace();
       }
     }
 }

10.DataSource和RowSet简介

　　随着J2EE的标准而出现，经常和企业级应用关联在一块。

题外话：

a.找不到安装程序时先不要搜索，去程序中找属性。
b.命令行下要想使用外部jar，则需要加进入classpath；普通的java工程使用外部jar文件需要右键--build path--add external archives；最好放在自己的某一工程下不要放在系统下，防止新旧文件或者和其他人的文件冲突，这也属于耦合性的降低。
c.java.sql.*中Connection是接口，算是一流的公司卖标准，年年收专利费；但是做出让人人都遵守的接口也不容易。