How to correctly implement a DAO in a GWT web app?

问题

I have a couple of questions to be answered relating DAOs and GWT. I'm implementing a DAO class in the GWT project and I want to use it when a button is pressed, like this: (inside the .java GWT class)

      lookUpButton.addClickHandler(new ClickHandler() {
        public void onClick(ClickEvent event) {
              lookup();
            }
          });  
    ...    ...     ...
       private void lookup() {
          PersonDao dao = new PersonDao();
          Person m = dao.getPerson(3); //hard-coded the pk of the person
          resultsFlexTable.setText(1, 0, m.toString());

I get two problems here, the first is practical, when I compile the project, I get an error and it just says "failed, try again" in my browser and I cannot run it.
The second question I have is this: Is it really a good practice to use a DAO in a GWT class given that it compiles directly into AJAX? Or should I send a request to a servlet that has said DAO and performs the data access itself?
Does GWT provide an easy to understand (for a beginner) and better way to access a MySQL database to get data?

(Context: I'm trying to build a basic search engine for a database and I need to access said data from a GWT widget. I'm learning Java web development, and I've learnt about .jsp, Servlets, and some more basic stuff like DAOs. For college, I have to build as a final project a web application which necessarily must be using the GWT Framework.) I've already tried the documentation but I cannot really get through this, I'm stuck.

回答1:

This is not how gwt will work .... you can not simply write DAO layer call at UI side,

GWT is divided into 3 parts - to write the code

Client - to write the UI code
Shared - to write shared code which will be used in client as well as server side for ex - Model/Pojo classes
Server - to write services / function / JDBC methods

It should always be this way -

There are so many sample applications and examples available over sites.

There is one simple example here - https://github.com/davisford/gwt-demo/tree/master/src/main/java/com/example

来源：https://stackoverflow.com/questions/54155300/how-to-correctly-implement-a-dao-in-a-gwt-web-app

标签

java

servlets

gwt

dao