批处理和获取主键值

批处理：

  1)想发送多条SQL，又要降低与数据库系统的交互，这时使用批处理
  2)Statement对象：适合对不同结构的SQL做批处理操作

  3)PreparedStatement对象：适合对相同结构的SQL做批处理操作

采用PreparedStatement.addBatch()实现批处理

优点：发送的是预编译后的SQL语句，执行效率高。
缺点：只能应用在SQL语句相同，但参数不同的批处理中。因此此种形式的批处理经常用于在同一个表中批量插入数            据，或批量更新表的数据。

案例：

//Statement和PreparedStatment的批处理public class Demo3 {public static void statementBatch() {Connection conn = null;Statement stmt = null;ResultSet rs = null;String insertSQL = "insert into user(username,password,birthday,salary) values('jack','000111','2011-10-26',5000)";String updateSQL = "update user set username='杰克' where username='jack'";try {conn = JdbcUtil.getMySqlConnection();stmt = conn.createStatement();//将需要执行的多条命令加入到批对象中stmt.addBatch(insertSQL);stmt.addBatch(updateSQL);//一次性发送批对象到数据库端执行,返回每条SQL的结果int[] is = stmt.executeBatch();//将批对象清空stmt.clearBatch();//显示结果System.out.println(is[0]+":"+is[1]);} catch (Exception e) {e.printStackTrace();}finally{JdbcUtil.close(rs);JdbcUtil.close(stmt);JdbcUtil.close(conn);}}public static void preparedBatch() {Connection conn = null;PreparedStatement pstmt = null;ResultSet rs = null;String insertSQL = "insert into user(username,password,birthday,salary) values(?,?,?,?)";try {conn = JdbcUtil.getMySqlConnection();pstmt = conn.prepareStatement(insertSQL);long begin = System.currentTimeMillis();for(int i=1;i<=1000;i++){pstmt.setString(1,"jack"+i);pstmt.setString(2,"111111");pstmt.setDate(3,new java.sql.Date(12345));pstmt.setFloat(4,5000);//加入到批对象中pstmt.addBatch();if(i%100==0){//执行批对象pstmt.executeBatch();//清空批对象pstmt.clearBatch();}}//执行批对象pstmt.executeBatch();//清空批对象pstmt.clearBatch();long end = System.currentTimeMillis();System.out.println((end-begin)/1000+"秒");} catch (Exception e) {e.printStackTrace();}finally{JdbcUtil.close(rs);JdbcUtil.close(pstmt);JdbcUtil.close(conn);}}public static void main(String[] args) {//statementBatch();preparedBatch();}}

获取数据库主键值

  1)当需要获取刚插入主键信息的时候，需要使用获取主键值方法
  2)关键代码：
pstmt = conn.prepareStatement(sqlA,Statement.RETURN_GENERATED_KEYS);
rs = pstmt.getGeneratedKeys();
if(rs.next()){
Long temp = (Long) rs.getObject(1);
pid = temp.intValue();
}

public class Dao {public void save(Person p) throws SQLException {//思路Connection conn = null;PreparedStatement pstmt = null;ResultSet rs = null;conn = JdbcUtil.getMySqlConnection();String sqlA = "insert into person(name) values(?)";String sqlB = "insert into card(location,pid) values(?,?)";//NO1，向person表插入一条记录pstmt = conn.prepareStatement(sqlA,Statement.RETURN_GENERATED_KEYS);pstmt.setString(1,p.getName());pstmt.executeUpdate();int pid = 0;//NO2，取得插入记录的主键值rs = pstmt.getGeneratedKeys();if(rs.next()){Long temp = (Long) rs.getObject(1);pid = temp.intValue();}//NO3，向card表插入一条记录pstmt = conn.prepareStatement(sqlB);pstmt.setString(1,p.getCard().getLocation());pstmt.setInt(2,pid);pstmt.executeUpdate();//非空关闭流JdbcUtil.close(rs);JdbcUtil.close(pstmt);JdbcUtil.close(conn);}}