GET vs POST in Java Web Services

1. Introduction

In the context of Java web services, GET and POST are two HTTP methods clients use 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
Mainly used for retrieving data. It is idempotent, meaning that multiple identical requests should have the same effect as a single request.	It is used for submitting data to be processed (e.g., creating or updating resources). It is not idempotent.
Parameters are appended to the URL, making them visible in the browser's address bar.	Parameters are included in the request body and not visible in the URL.
It can be bookmarked and cached.	It cannot be bookmarked or cached.
A limited amount of data can be sent because the URL has a length limit.	No size limitations for the data sent, allowing for large amounts of data to be transferred.
Less secure compared to POST because data is exposed in the URL. Suitable for non-sensitive data.	More secure for sensitive data as parameters are not stored in browser history or web server logs.
Examples include searching, retrieving articles, or downloading files where the action does not change the resource's state.	Examples include login forms, data entry forms, and uploading files, where the server's state might change due to the action.

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 sending data to the server, such as submitting a form, uploading a file, or updating a resource.