Class.forName("com.mysql.jdbc.Driver");
   Connection conn = DriverManager
    .getConnection("jdbc:mysql://localhost/BBS?user=root&password=root");    //连接数据库
conn.setAutoCommit(false);       //不自动提交
   
String sql = "insert into article values (null,0,?,?,?,now(),0)";
PreparedStatement pstat = conn.prepareStatement(sql,Statement.RETURN_GENERATED_KEYS);

//创建一个默认 PreparedStatement 对象，该对象能获取自动生成的键，适合insert语句
//（该语句能自动生成键值）autoGeneratedKeys - 指示是否应该返回自动生成的键的标志


Statement stat = conn.createStatement();

pstat.setInt(1, -1);
pstat.setString(2,title);
pstat.setString(3,content);
pstat.executeUpdate();

ResultSet rsKey = pstat.getGeneratedKeys();      //ResultSet 指示键值
rsKey.next();
int key = rsKey.getInt(1);     //得到第一个键值
stat.executeUpdate("update article set rootid = " + key + " where id = " + key);

conn.commit();
conn.setAutoCommit(true);     //设回自动提交