Dinesh on Java

JSP

JSP Form Processing

You must have come across many situations when you need to pass some information from your browser to web server and ultimately to your back-end program. The browser uses two methods to pass this information to web server. These methods are GET Method and POST Method.
GET method:
The GET method sends the encoded user information appended to the page request. The page and the encoded information are separated by the ? character as follows:https://www.dineshonjava.com/hello?key1=value1&key2=value2

The GET method is the default method to pass information from browser to web server and it produces a long string that appears in your browser’s Location:box. Never use the GET method if you have password or other sensitive information to pass to the server.

The GET method has size limitation: only 1024 characters can be in a request string.

This information is passed using QUERY_STRING header and will be accessible through QUERY_STRING environment variable which can be handled using getQueryString() and getParameter() methods of request object.

POST method:
A generally more reliable method of passing information to a backend program is the POST method.

This method packages the information in exactly the same way as GET methods, but instead of sending it as a text string after a ? in the URL it sends it as a separate message. This message comes to the backend program in the form of the standard input which you can parse and use for your processing.

JSP handles this type of requests using getParameter() method to read simple parameters and getInputStream() method to read binary data stream coming from the client.

Reading Form Data using JSP
JSP handles form data parsing automatically using the following methods depending on the situation:

getParameter(): You call request.getParameter() method to get the value of a form parameter.
getParameterValues(): Call this method if the parameter appears more than once and returns multiple values, for example checkbox.
getParameterNames(): Call this method if you want a complete list of all parameters in the current request.
getInputStream(): Call this method to read binary data stream coming from the client.

GET Method Example Using URL:
Here is a simple URL which will pass two values to HelloForm program using GET method.

http://localhost:8080/myapp/index.jsp?first_name=Dinesh&last_name=Rajput

Below is index.jsp JSP program to handle input given by web browser. We are going to use getParameter() method which makes it very easy to access passed information:

<html>
<head>
<title>Using GET Method to Read Form Data</title>
</head>
<body>
<center>
<h1>Using GET Method to Read Form Data</h1>
<ul>
<li><p><b>First Name:</b>
   <%= request.getParameter("first_name")%>
</p></li>
<li><p><b>Last  Name:</b>
   <%= request.getParameter("last_name")%>
</p></li>
</ul>
</body>
</html>

Now open following url-
http://localhost:8080/myapp/index.jsp?first_name=Dinesh&last_name=Rajput

GET Method Example Using Form:
Here is a simple example which passes two values using HTML FORM and submit button. We are going to use same JSP index.jsp to handle this input.
getRequestParam.jsp

<html>
<body>
<form action="index.jsp" method="GET">
First Name: <input type="text" name="first_name">
<br />
Last Name: <input type="text" name="last_name" />
<input type="submit" value="Submit" />
</form>
</body>
</html>

Hit URL:
http://localhost:8080/myapp/getRequestParam.jsp

Try to enter First Name and Last Name and then click submit button to see the result on your local machine where tomcat is running. Based on the input provided, it will generate similar result as mentioned in the above example.

http://localhost:8080/myapp/index.jsp?first_name=Dinesh&last_name=Rajput

POST Method Example Using Form:
Let us do little modification in the above JSP to handle GET as well as POST methods. Below is index.jsp JSP program to handle input given by web browser using GET or POST methods.

Infact there is no change in above JSP because only way of passing parameters is changed and no binary data is being passed to the JSP program. File handling related concepts would be explained in separate chapter where we need to read binary data stream.

<html>
<head>
<title>Using GET and POST Method to Read Form Data</title>
</head>
<body>
<center>
<h1>Using GET Method to Read Form Data</h1>
<ul>
<li><p><b>First Name:</b>
   <%= request.getParameter("first_name")%>
</p></li>
<li><p><b>Last  Name:</b>
   <%= request.getParameter("last_name")%>
</p></li>
</ul>
</body>
</html>

getRequestParam.jsp

<html>
<body>
<form action="main.jsp" method="POST">
First Name: <input type="text" name="first_name">
<br />
Last Name: <input type="text" name="last_name" />
<input type="submit" value="Submit" />
</form>
</body>
</html>

http://localhost:8080/myapp/getRequestParam.jsp

http://localhost:8080/myapp/index.jsp?first_name=Dinesh&last_name=Rajput

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Dinesh Rajput

Dinesh Rajput is the chief editor of a website Dineshonjava, a technical blog dedicated to the Spring and Java technologies. It has a series of articles related to Java technologies. Dinesh has been a Spring enthusiast since 2008 and is a Pivotal Certified Spring Professional, an author of a book Spring 5 Design Pattern, and a blogger. He has more than 10 years of experience with different aspects of Spring and Java design and development. His core expertise lies in the latest version of Spring Framework, Spring Boot, Spring Security, creating REST APIs, Microservice Architecture, Reactive Pattern, Spring AOP, Design Patterns, Struts, Hibernate, Web Services, Spring Batch, Cassandra, MongoDB, and Web Application Design and Architecture. He is currently working as a technology manager at a leading product and web development company. He worked as a developer and tech lead at the Bennett, Coleman & Co. Ltd and was the first developer in his previous company, Paytm. Dinesh is passionate about the latest Java technologies and loves to write technical blogs related to it. He is a very active member of the Java and Spring community on different forums. When it comes to the Spring Framework and Java, Dinesh tops the list!