JDBC 查询步骤

JDBC 查询步骤 

 

1、读取配置文件：

//注意此代码是写在一个静态代码块中，以确保数据库在加载该类中的实例之前就已经加载完成
private static DataSource dataSource;
 
 static {  Properties props = new Properties();  try {   props.load(DbUtil.class.getClassLoader().getResourceAsStream(     "dbcp.properties"));//数据库的数据配置文件路径   dataSource = BasicDataSourceFactory.createDataSource(props);  } catch (Exception e) {   e.printStackTrace();  } }
 

2、获取JDBC的链接

private static ThreadLocal<Connection> connLocal = new ThreadLocal<Connection>();
 
public synchronized static Connection getConnection() throws Exception {  Connection conn = connLocal.get();  if (conn == null) {   conn = dataSource.getConnection();   connLocal.set(conn);  }  return conn; } 

3、执行数据的操作

//数据的删除操作
private static final String ADD_NEW_USER="insert into d_user values(?,?)"; public void intoNew(User u) throws Exception{  Connection conn=DbUtil.getConnection();  PreparedStatement pst=conn.prepareStatement(ADD_NEW_USER);  pst.setString(1, u.getUsername());  pst.setString(2, u.getPassword());  pst.executeUpdate();
 
//数据的查询和遍历操作
privatestaticfinal String FIND_COURSE="select *from d_cate where parent_id>0";
public List<Cate> findCourse() throws Exception {
Connection conn=DbUtil.getConnection();
System.out.println(conn);
PreparedStatement pst=conn.prepareStatement(FIND_COURSE);
ResultSet rs=pst.executeQuery();
List<Cate> list=new ArrayList<Cate>();
while(rs.next()){
Cate c=new Cate();
c.setId(rs.getInt("id"));
c.setName(rs.getString("name"));
c.setFileName(rs.getString("filename"));
c.setParentId(rs.getInt("parent_id"));
list.add(c);
}
return list;
}
 
//数据的更新操作
 
privatefinalstatic String DELETE_APP="delete from d_application where id=?";
publicvoid delete(int id) throws Exception{
Connection conn=DbUtil.getConnection();
PreparedStatement pst=conn.prepareStatement(DELETE_APP);
pst.setInt(1, id);
pst.executeUpdate();
}

4、数据库连接需要的perporties文件配置

// mySql
driverClassName=com.mysql.jdbc.Driverurl=jdbc\:mysql\://localhost\:3306/classusername=rootpassword=gkzx#初始创建connection的数量initialSize=3#最多创建connection的数量maxActive=15#空闲connection的最大值maxIdle=2#空闲connection的最小值minIdle=1#没有可用connection时,等待最大值maxWait=30000