Send and handle HTTP request in Java

CodeCat1024 — Thu, 23 Feb 2023 13:50:47 +0000

Send requests

You can send requests by listed ways.

Tag a or broswer and so son

They are all make a GET request method.

Postman

You can use Postman to make any requests.

Form Input

You can use any request methods by using attribute method.

And the attribute action represent the URI where the form will sumbit.

<form action="postGetParameter" method="post">
    <input type="text" name="userId">
    <input type="password" name="password">
    <input type="submit" value="sumbit">
</form>

Ajax

We needn't form tag by this way.

Because you can set the method and the action in JS code.

<input type="text" id="userId">
<input type="text" id="classId">
<input type="button" value="sumbit" id="submit">

let userIdInput = document.querySelector("#userId");
let classIdInput = document.querySelector("#classId");
let button = document.querySelector("#sumbit");
button.onclick = function(){
    $.ajax({
        type: 'post',
        url: 'path',
        data: JSON.stringify({
            userId: userIdInput.value,
            classId: classIdInput.value
        }),
        success: function(body){
            console.log(body);
        }
    });
}

Handle requests in Java

We can use three classes to handle requests in servlet.

HttpServlet

class User {
    //You must need to note the types.
    //If you wrote a String, but you send a int, it will throw a exception.
    public String userId;
    public String classId;
}

@WebServlet("/path")
public class HelloServlet extends HttpServlet {

    private ObjectMapper objectMapper = new ObjectMapper();

    @Override
    protected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
       //You must to comment this method otherwise your codes will goes wrong
       //super.doGet(req, resp);

       //And you must add the setContentType method if you want to print in Chinese.
       resp.setContentType("text/html; charset=utf8");
       //You can use this method to print something to the console of the broswer
      resp.getWriter().write("Hello Servlet");


       //HANDLE THE STRING
       String userId = req.getParameter("userId");
       String classId = req.getParameter("classId");
       resp.getWriter().write("userId: " + user.userId + "classId: " + user.classId);

        //HANDLE THE JSON STRING
        //The first parameter, you can give a String or a InputStream Object
        //The second parameter, present what object you want t make and then you will get a class.
        User user = objectMapper.readValue(req.getInputStream(), User.class);
        resp.getWriter().write("userId: " + user.userId + "classId: " + user.classId);
    }
}

HttpServletRequest and HttpServletResponse

Servlet provides two classes let we to operate attributes of Request and Response.

They have many methods provied let you to operate.

You can search these methods in google.

body format

The data body have three formats when you use post method.

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