[英]how to retrieve data from database in servlet
im beginners in java servlet... i working on curd operation... ...data not displaying please tell me where im wrong.... 即时消息Java Servlet的初学者...我正在进行凝乳操作... ...数据未显示,请告诉我即时消息错了....
DAO.java DAO.java
public void select(){
try{
Class.forName(jdbcDriver);
Connection conn = DriverManager .getConnection(connectionString,username,password);
PreparedStatement create = conn.prepareStatement("select * from student.users");
ResultSet rs;
rs = create.executeQuery();
while(rs.next()){
int id =rs.getInt("id");
String name = rs.getString("fname");
}
}
catch(Exception e){
e.printStackTrace();
}
}
servlet.java servlet.java
DAO user = new DAO(); /// i create object of DAO
user.select(); //calling select method
out.write("<td>");
out.write("<p>"+user.id+"</p>"); ///tried many from different way
out.write("</td>");
out.write("<td>");
out.write("<p>"+user.name+"</p>"); ///
out.write("</td>");
i tried many from different way but no luck.... can you tell me where I'm wrong 我以不同的方式尝试了很多,但没有运气。...你能告诉我我错了吗
I see some problems there. 我在那里看到了一些问题。 First i think your select method should return a List of users. 首先,我认为您的select方法应该返回用户列表。 So you can implement that as bellow 所以你可以像下面这样实现
public List<User> select(){
List<User> result = new ArrayList<User>();
try{
Class.forName(jdbcDriver);
Connection conn = DriverManager .getConnection(connectionString,username,password);
PreparedStatement create = conn.prepareStatement("select * from student.users");
ResultSet rs;
rs = create.executeQuery();
while(rs.next()){
int id =rs.getInt("id");
String name = rs.getString("fname");
User user = new User(); // Creating a user object to fill with user data (I imagine that you have a user class in your model)
user.setId(id);
user.setName(name);
//Add the retrived user to the list
result.add(user);
}
//Returning the list of users.
return result;
}catch(Exception e){
e.printStackTrace();
return null;
}
}
So in your servlet you can call this method to return this list and show it. 因此,在您的Servlet中,您可以调用此方法以返回此列表并显示它。
DAO daoUser = new DAO(); /// i create object of DAO
List<User> users = daoUser.select(); //calling select to get list of users
out.write("<table>");
for(User user : users){ //Running through the list to show all users retrived
out.write("<td>");
out.write("<p>"+user.id+"</p>");
out.write("</td>");
out.write("<td>");
out.write("<p>"+user.name+"</p>"); ///
out.write("</td>");
}
out.write("</table>");
So that's it. 就是这样了。 The logic it's that i'm not sure if it will work, may a forget some detail but this is the way to do. 逻辑是我不确定它是否会工作,可能会忘记一些细节,但这是这样做的方法。 Hope that helps. 希望能有所帮助。
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