Selecting only one record (Javabean, setAttribute, getAttribute, SQL, servlet)

Question

I created a new bean called client with Id , Name , LastName and Address fields. I created the model and the view of course. My model returns a list of all the clients. And this one is working fine.

But I need a model where I can select only one specific client filtered by Id . Can anybody tell me what I need to change (besides the SQL statement) inside this model so I get only one client according to filter (id) criteria from SQL?

{
    Connection connection = getDatabaseConnection();
    request.setAttribute("clientList", getClientList(connection));
    closeDatabaseConnection(connection);
}

private ArrayList<Client> getClientList(Connection con)
{
    String sqlstr = "SELECT * FROM Clients";
    PreparedStatement stmt = null;
    ResultSet rs = null;
    ArrayList<Client> clients = new ArrayList<Client>();

    try
    {
        stmt = con.prepareStatement(sqlStr);
        rs = stmt.executeQuery();

        while (rs.next())
        {
            Client client = new Client();
            client.setId(rs.getInt("Id"));
            client.setName(rs.getString("Name"));
            client.setLastName(rs.getString("LastName"));
            client.setAddress(rs.getString("Address"));

            clients.add(client);
        }

        rs.close();
        stmt.close();
    }
    catch (SQLException sqle)
    {
        sqle.printStackTrace();
    }
    finally
    {
        return clients;
    }
}

Answer 1

除了sql语句，您还意味着什么？您必须在查询中添加where子句，我认为没有其他可能的情况。

Answer 2

Well, I guess you already have a class with a method that you invoke to retrieve all the cliets, right?

Well, now add another method, but this time a method that receives the client Id as parameter:

public List<Client> getAllClients();
public Client getClientById(int clientId);

You will need a secondary SQL statement, since the logic in the first one is for retrieving all records. Something like:

"select clientId, clientName, ... from clients where clientId=?"

Using a JDBC PreparedStatement you can easily replace the ? for the actual parameter being received by your API.

You can also consider abstracting your mapping strategy so that you can use it for both methods:

class ClientMapper implements SqlMapper<Client> {
    @Override
    public Client map(ResultSet rs) throws SQLException {
       Client client = new Client();
       client.setId(rs.getInt("Id"));
       client.setName(rs.getString("Name"));
       client.setLastName(rs.getString("LastName"));
       client.setAddress(rs.getString("Address"));
       return client;
    }
}

You can also have a ClientsMapper that uses this single client mapper to retrieve all clients.

class ClientsMapper implements SqlMapper<List<Client>>{
   @Override
   public List<Client> map(ResultSet rs){
     List<Client> result = new ArrayList<>();
     ClientMapper mapper = new ClientMapper();
     while(rs.next()){
        result.add(mapper.map(rs));
     }
     return result;
   }
}

Answer 3

well you can have one more method that returns a single client based on the id you provide as argument.

 public Client getClientById(int id){
    //fetch the client data using the id

    //make a local Client object
    Client c = new Client();

    //populate c based on the values you get from your database.

    //return this local object of Client
    return c;

 }