java 如何在servlet中从数据库中检索数据
声明：本页面是StackOverFlow热门问题的中英对照翻译，遵循CC BY-SA 4.0协议，如果您需要使用它，必须同样遵循CC BY-SA许可，注明原文地址和作者信息，同时你必须将它归于原作者（不是我）：StackOverFlow
原文地址: http://stackoverflow.com/questions/32000430/
Warning: these are provided under cc-by-sa 4.0 license. You are free to use/share it, But you must attribute it to the original authors (not me):
StackOverFlow
how to retrieve data from database in servlet
提问by Asad
im beginners in java servlet... i working on curd operation... ...data not displaying please tell me where im wrong....
我是 Java servlet 的初学者……我正在研究豆腐操作…………数据不显示，请告诉我我错在哪里……
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
我从不同的方式尝试了很多但没有运气....你能告诉我我错在哪里吗
采纳答案by Luciano Almeida
I see some problems there. First i think your select method should return a List of users. So you can implement that as bellow
我看到那里有些问题。首先，我认为您的 select 方法应该返回一个用户列表。所以你可以实现如下
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，您可以调用此方法来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. 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. Hope that helps.
就是这样了。逻辑是我不确定它是否会起作用，可能会忘记一些细节，但这是方法。希望有帮助。
