Difference between GET and POST in Java Web Services

1. Introduction

In the context of Java web services, GET and POST are two HTTP methods used by clients to send requests to the server. The GET method requests data from a specified resource and should only retrieve data without causing any other effect. The POST method sends data to the server to create or update a resource.

2. Key Points

1. GET is used for requesting data from a specific resource and should be idempotent (not causing any side effects).

2. POST is used for sending data to a server to create/update a resource and is not idempotent.

3. Data sent by GET is visible in the URL, whereas data sent by POST is included in the request body and not displayed in the URL.

4. GET requests can be cached and bookmarked, while POST requests cannot.

3. Differences

GET	POST
Used to retrieve data.	Used to send data for creating or updating.
Parameters included in URL.	Parameters are included in the body of the request.
Can be bookmarked and cached.	Cannot be bookmarked or cached.
Has length restrictions.	No restrictions on data length.

4. Example

// Example of a GET request in a Java servlet
protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
    String param = request.getParameter("param");
    response.getWriter().write("GET request with param: " + param);
}

// Example of a POST request in a Java servlet
protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
    String param = request.getParameter("param");
    // Assume we create a resource with the parameter we received
    response.getWriter().write("POST request with param: " + param);
}

Output:

// Output for GET request
GET request with param: value
// Output for POST request
POST request with param: value

Explanation:

1. The doGet method handles a GET request, retrieving the parameter from the query string in the URL and responding with that parameter.

2. The doPost method handles a POST request, retrieving the parameter from the request body and could use that data to create or update a resource.

5. When to use?

- Use GET when you need to retrieve data from the server without causing any side effects, like in a search or when fetching a specific resource.

- Use POST when you need to send data to the server, such as submitting a form, uploading a file, or updating a resource.