SP (JavaServer Pages) pages are essentially HTML files with embedded Java code. To rewrite JSP pages in Java, you will need to extract the Java code from the JSP pages and refactor it into Java code files that can be compiled and run independently.

Here are the steps to follow:

  1. Identify the Java code in your JSP pages. This code will be enclosed in <% %> tags or <%= %> tags.

  2. Extract the Java code from the JSP pages and refactor it into Java classes or methods.

  3. Create a Java class for each JSP page. This class will have methods that contain the Java code extracted from the JSP page.

  4. In each Java class, create a method that generates the HTML output that was previously generated by the JSP page. This can be done using a StringBuilder or other similar class to build up the HTML output.

  5. Compile the Java classes and run them to test that they generate the correct output.

  6. Modify your web application to call the appropriate Java class instead of the JSP page.

  7. Update your web server configuration to serve the new Java classes instead of the JSP pages.

Keep in mind that rewriting JSP pages in Java can be a time-consuming process, especially if you have a large number of pages. However, it can lead to improved performance and maintainability of your web application.

here's an example of how to rewrite a simple JSP page in Java:

JSP Page (hello.jsp):

<html>
<head>
	<title>Hello World</title>
</head>
<body>
	<%
		String name = request.getParameter("name");
		if (name == null) {
			name = "World";
		}
	%>
	<h1>Hello <%= name %>!</h1>
</body>
</html>

Java Class (HelloServlet.java):

import java.io.IOException;
import javax.servlet.ServletException;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;

public class HelloServlet extends HttpServlet {
	private static final long serialVersionUID = 1L;

	protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
		String name = request.getParameter("name");
		if (name == null) {
			name = "World";
		}
		String output = "<html><head><title>Hello World</title></head><body><h1>Hello " + name + "!</h1></body></html>";
		response.setContentType("text/html");
		response.getWriter().write(output);
	}
}

Explanation: In this example, we have a JSP page that accepts a parameter called "name" and displays a personalized message. The embedded Java code inside the JSP page retrieves the value of the "name" parameter and sets a default value if it's not provided.

To rewrite this JSP page in Java, we create a new servlet class called HelloServlet that extends the HttpServlet class. We override the doGet() method, which is called when the servlet receives a GET request.

Inside the doGet() method, we retrieve the value of the "name" parameter and set a default value if it's not provided. We then build up the HTML output using a String variable, and finally write the output to the HttpServletResponse object using the getWriter() method.

Note that in the Java class version, we have complete control over the HTML output and can build it up using any Java constructs or libraries that we want, whereas in the JSP version we are limited to the JSP syntax and constructs.