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36

Chapter 2 First Servlets

console. For examples of these settings, see Section 2.7 (An Example Using

Initialization Parameters).

The second thing to note about the second version of 

init

 is that the first

line of the method body is a call to 

super.init

. This call is critical! The

ServletConfig

 object is used elsewhere in the servlet, and the 

init

 method

of the superclass registers it where the servlet can find it later. So, you can

cause yourself huge headaches later if you omit the 

super.init

 call.

Core Approach

If you write an 

init

 method that takes a 

ServletConfig

 as an 

argument, 

always

 call 

super.init

 on the first line.

The service Method

Each time the server receives a request for a servlet, the server spawns a new

thread and calls 

service

. The 

service

 method checks the HTTP request

type (

GET

, 

POST

, 

PUT

, 

DELETE

, etc.) and calls 

doGet

, 

doPost

, 

doPut

, 

doDe 

lete

, etc., as appropriate. Now, if you have a servlet that needs to handle

both 

POST

 and 

GET

 requests identically, you may be tempted to override 

ser 

vice

 directly as below, rather than implementing both 

doGet

 and 

doPost

.

public void service(HttpServletRequest request,

HttpServletResponse response)

throws ServletException, IOException {

// Servlet Code

}

This is not a good idea. Instead, just have 

doPost

 call 

doGet

 (or vice

versa), as below.

public void doGet(HttpServletRequest request,

HttpServletResponse response)

throws ServletException, IOException {

// Servlet Code

}

public void doPost(HttpServletRequest request,

 HttpServletResponse response)

throws ServletException, IOException {

doGet(request, response);

}

Although this approach takes a couple of extra lines of code, it has five

advantages over directly overriding 

service

:

Second edition of this book: www.coreservlets.com; Sequel: www.moreservlets.com.

Servlet and JSP training courses by book's author: courses.coreservlets.com.