AppPerfect

Java Servlet Code

Rules available in this category:

  1. Reuse_data_sources_in_servlets
  2. Avoid_assigning_values_to_instance_field_without_acquiring_lock
  3. Avoid_assigning_values_to_static_instance_field_without_acquiring_lock
  4. Avoid_calling_Beans_instantiate_to_create_new_bean_instances
  5. Minimize_use_of_System_out_println_or_System_err_println
  6. Always_invalidate_local_HTTP_session_objects
  7. Use_context_objects_to_handle_HTTP_request_parameters
  8. Avoid_storing_non_serializable_object_into_HttpSession
  9. Avoid_using_SingleThreadModel
  10. Avoid_using_instance_variables_in_Servlets
  11. Do_not_declare_service_methods_synchronized
  12. Define_default_public_constructor_for_servlet
  13. Minimize_synchronization_in_servlets
Rule 1: Reuse_data_sources_in_servlets

Severity:  Medium
Rule:  Always reuse the data sources in servlets.
Reason:  Always reuse the data sources in servlets.

Usage Example: 

package com.rule;

import java.io.IOException;
import java.sql.Connection;

import javax.naming.InitialContext;
import javax.servlet.ServletException;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import javax.sql.DataSource;

public class Reuse_data_sources_in_servlets_violation extends HttpServlet
{
protected void doPost(HttpServletRequest arg0, HttpServletResponse arg1) throws ServletException, IOException
{
try
{
InitialContext ic = new InitialContext();
DataSource dataSource = (DataSource)ic.lookup("jdbc/pool/OracleDS"); // VIOLATION
Connection connection = dataSource.getConnection();
// database handling
}
catch (Exception e)
{
// handle exception
}
}
}

Should be written as:

package com.rule;

import java.io.IOException;
import java.sql.Connection;

import javax.naming.InitialContext;
import javax.servlet.ServletException;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import javax.sql.DataSource;

public class Reuse_data_sources_in_servlets_correction extends HttpServlet
{
private DataSource dataSource;

public void init() throws ServletException
{
try
{
InitialContext ic = new InitialContext();
dataSource = (DataSource)ic.lookup("jdbc/pool/OracleDS"); // CORRECTION
}
catch (Exception e)
{
// handle exception
}
}

protected void doPost(HttpServletRequest arg0, HttpServletResponse arg1) throws ServletException, IOException
{
try
{
Connection connection = dataSource.getConnection();
// database handling
}
catch (Exception e)
{
// handle exception
}
}
}

Reference:  http://www.geocities.com/javabestpractices/servlet.html
http://www-306.ibm.com/software/webservers/appserv/ws_bestpractices.pdf

Rule 2: Avoid_assigning_values_to_instance_field_without_acquiring_lock

Severity:  Medium
Rule:  Since servlet instance fields are accessed by various threads, one should acquire a lock prior to assigning the field to avoid the common race conditions and data cross-over in J2EE applications.
Reason:  Since servlet instance fields are accessed by various threads, one should acquire a lock prior to assigning the field to avoid the common race conditions and data cross-over in J2EE applications.

Usage Example: 

private String userId = Smith";

public void doGet(HttpServletRequest req, HttpServletResponse res) throws IOException 
{
PrintWriter out = res.getWriter();
HttpSession session = req.getSession();
String user = (String)session.getAttribute("name");
setUser(user);
// ...
out.println("<HTML><HEAD><TITLE>Servlet that writes to an instance  field</TITLE></HEAD><BODY>");
out.println("UserId: "+userId+"</BODY></HTML>");
out.close();
session.invalidate();
}

private void setUser(String user)
{
userId = user;  // VIOLATION
}

Should be written as:

private String userId = Smith";

public void doGet(HttpServletRequest req, HttpServletResponse res) throws IOException 
{
PrintWriter out = res.getWriter();
HttpSession session = req.getSession();
String user = (String)session.getAttribute("name");
setUser(user);
// ...
out.println("<HTML><HEAD><TITLE>Servlet that writes to an instance  field</TITLE></HEAD><BODY>");
out.println("UserId: "+userId+"</BODY></HTML>");
out.close();
session.invalidate();
}

private void setUser(String user)
{
synchronized ( userId ) // CORRECTION
{
userId = user; 
}
}

Reference:  No references available.

Rule 3: Avoid_assigning_values_to_static_instance_field_without_acquiring_lock

Severity:  Medium
Rule:  Since servlet static instance fields are accessed by various threads, one should acquire a lock prior to assigning the field to avoid the common race conditions and data cross-over in J2EE applications.
Reason:  Since servlet static instance fields are accessed by various threads, one should acquire a lock prior to assigning the field to avoid the common race conditions and data cross-over in J2EE applications.

Usage Example: 

private static String userId = Smith";

public void doGet(HttpServletRequest req, HttpServletResponse res) throws IOException 
{
PrintWriter out = res.getWriter();
HttpSession session = req.getSession();
String user = (String)session.getAttribute("name");
setUser(user);
// ...
out.println("<HTML><HEAD><TITLE>Servlet that writes to an instance  field</TITLE></HEAD><BODY>");
out.println("UserId: "+userId+"</BODY></HTML>");
out.close();
session.invalidate();
}

private void setUser(String user)
{
userId = user;  // VIOLATION
}

Should be written as:

private static String userId = Smith";

public void doGet(HttpServletRequest req, HttpServletResponse res) throws IOException 
{
PrintWriter out = res.getWriter();
HttpSession session = req.getSession();
String user = (String)session.getAttribute("name");
setUser(user);
// ...
out.println("<HTML><HEAD><TITLE>Servlet that writes to an instance  field</TITLE></HEAD><BODY>");
out.println("UserId: "+userId+"</BODY></HTML>");
out.close();
session.invalidate();
}

private void setUser(String user)
{
synchronized ( userId ) // CORRECTION
{
userId = user; 
}
}

Reference:  No references available.

Rule 4: Avoid_calling_Beans_instantiate_to_create_new_bean_instances

Severity:  Medium
Rule:  Each time java.beans.Beans.instantiate is called the file system is checked for a serialized version of the bean.
Reason:  Each time java.beans.Beans.instantiate is called the file system is checked for a serialized version of the bean.

Usage Example: 

import javax.servlet.http.*;
import java.beans.*;

public class MyServlet extends HttpServlet {
 public void doGet (HttpServletRequest request) throws ClassNotFoundException
  , java.io.IOException
 {
 Beans b = (Beans)Beans.instantiate (this.getClass ().getClassLoader ()
, "web_prmtv.Bean");// VIOLATION
 }
}

Should be written as:

import javax.servlet.http.*;
import java.beans.*;

public class MyServlet extends HttpServlet {
 public void doGet (HttpServletRequest request) throws ClassNotFoundException
  , java.io.IOException
 {
  Beans b = new Beans ();  // CORRECTION
 }
}

Reference:  http://www-4.ibm.com/software/webservers/appserv/ws_bestpractices.pdf

Rule 5: Minimize_use_of_System_out_println_or_System_err_println

Severity:  Low
Rule:  These calls should not be used in production unless the outputs are redirected to a log file.
Reason:  These calls should not be used in production unless the outputs are redirected to a log file.

Usage Example: 

import javax.servlet.*;
import javax.servlet.http.*;

public class MyClass extends HttpServlet 
{
public void service () 
{
  System.out.println ("Initiating Service");  // VIOLATION
}
}

Should be written as:

import javax.servlet.*;
import javax.servlet.http.*;

public class MyClass extends HttpServlet 
{
 private final static boolean DEBUG_ON = false;
 public void service () 
 {
  if (DEBUG_ON) 
 {
System.out.println ("starting service");  // CORRECTION
  }
 }

}

Reference:  http://www-4.ibm.com/software/webservers/appserv/ws_bestpractices.pdf

Rule 6: Always_invalidate_local_HTTP_session_objects

Severity:  Medium
Rule:  Always invalidate local HTTP Session objects.
Reason:  Always invalidate local HTTP Session objects.

Usage Example: 

import javax.servlet.*;
import javax.servlet.http.*;

public class AlwaysInvalidateLocalHTTPSessionObjects // VIOLATION
{
  
 public void session (HttpServletRequest request) 
{
  HttpSession mySession = request.getSession (false);
  String id = mySession.getId ();
  System.out.println ( id );
 }

}

Should be written as:

import javax.servlet.*;
import javax.servlet.http.*;

public class AlwaysInvalidateLocalHTTPSessionObjects 
{
 public void sessionFixed (HttpServletRequest request) 
 {
  HttpSession mySession = request.getSession (false);
  if (mySession != null) 
 {
String id = mySession.getId ();
System.out.println ( id );
mySession.invalidate ();  // CORRECTION
  }
 }
}

Reference:  IBM WebSphere Application Server Standard and Advanced Editions
IBM WebSphere Application Server Standard and Advanced Editions - by Harvey W. Gunther Date: September 7, 2000

Rule 7: Use_context_objects_to_handle_HTTP_request_parameters

Severity:  Medium
Rule:  Use context objects to handle HTTP request parameters for loose coupling.
Reason:  Use context objects to handle HTTP request parameters for loose coupling.

Usage Example: 

package examples.rules.servlet;

import javax.servlet.*;
import javax.servlet.http.*;

public class UCO extends HttpServlet 
{

 public void doGet(HttpServletRequest request,
HttpServletResponse response
 ) 
{
String first_name = request.getParameter("fname"); // VIOLATION
String last_name = request.getParameter("lname"); // VIOLATION
String email = request.getParameter("email"); // VIOLATION
 }
}

Should be written as:

package examples.rules.servlet;

import javax.servlet.*;
import javax.servlet.http.*;

public class UCOFixed extends HttpServlet 
{

 public void doGet(HttpServletRequest request,
HttpServletResponse response
 ) 
{
RequestContextFactory requestContextFactory =
 RequestContextFactory.getInstance();
  RequestContext requestContext = 
 requestContextFactory.createRequestContext(request);  // CORRECTION

String first_name = requestContext.getFirstName();
String last_name = requestContext.getLastName();
String email = requestContext.getEmail(); 
 }
}

class RequestContextFactory 
{
 private static RequestContextFactory _rcf;

 private RequestContextFactory() {  }

 static RequestContextFactory getInstance() 
{
if (_rcf == null) 
  {
_rcf = new RequestContextFactory();
}
return _rcf;
 }

RequestContext createRequestContext(ServletRequest request) 
{
String fn = validate(request.getParameter("fname"));
String ln = validate(request.getParameter("lname"));
String email = validate(request.getParameter("email"));
return new RequestContext(fn, ln, email);
 }
}

class RequestContext 
{

 private String _firstName;
 private String _lastName;
 private String _email;

 RequestContext(String fn, String ln, String email) 
{
_firstName = fn;
_lastName = ln;
_email = email;
 }

 final String getFirstName() 
{
return _firstName;
 }

 final String getLastName() 
{
return _lastName;
 }

 final String getEmail() 
{
return _email;
 }
}

Reference:  "Core J2EE Patterns - Best Practices and Design Strategies"
"Core J2EE Patterns - Best Practices and Design Strategies"
"Core J2EE Patterns - Best Practices and Design Strategies" - by Deepak Alur, John Cupri and Dan Malks. pp. 181

Rule 8: Avoid_storing_non_serializable_object_into_HttpSession

Severity:  Medium
Rule:  Avoid storing non serializable object into HttpSession.
Reason:  Avoid storing non serializable object into HttpSession.

Usage Example: 

package com.rule;

import javax.servlet.http.HttpSession;

class Avoid_storing_non_serializable_object_into_HttpSession_violation
{
Myclass obj = new Myclass();

public void method ()
{
HttpSession session = request.getSession(true);
String name = "AppPerfect";

session.setAttribute(name, obj); //Violation.
 }
}
class Myclass
{
// Class Variables ...

public Myclass()
{
// Initialising Class Variables ...
}

}

Should be written as:

package com.rule;

import javax.servlet.http.HttpSession;

class Avoid_storing_non_serializable_object_into_HttpSession_violation
{
Myclass obj = new Myclass();

public void method ()
{
HttpSession session = request.getSession(true);
String name = "AppPerfect";

session.setAttribute(name, obj);
 }
}
class Myclass implements Serializable //Correction.
{
// Class Variables ...

public Myclass()
{
// Initialising Class Variables ...
}

}

Reference:  Reference Not Available.

Rule 9: Avoid_using_SingleThreadModel

Severity:  Medium
Rule:  Do not use SingleThreadModel for servlets.
Reason:  Do not use SingleThreadModel for servlets.

Usage Example: 

package com.rule;

import javax.servlet.SingleThreadModel;
import javax.servlet.http.HttpServlet;

public class Avoid_using_SingleThreadModel_violation  // VIOLATION
extends HttpServlet
implements SingleThreadModel
{

}

Should be written as:

Use other means like synchronized blocks to handle multi threading issues in servlets.

Reference:  http://java.sun.com/j2ee/1.4/docs/api/javax/servlet/SingleThreadModel.html
http://www-306.ibm.com/software/webservers/appserv/ws_bestpractices.pdf

Rule 10: Avoid_using_instance_variables_in_Servlets

Severity:  Medium
Rule:  Avoid_using_instance_variables_in_Servlets.
Reason:  Avoid_using_instance_variables_in_Servlets.

Usage Example: 

package com.rule;

import javax.servlet.GenericServlet;
import javax.servlet.ServletRequest;
import javax.servlet.ServletResponse;

class Avoid_using_instance_variables_in_Servlets extends GenericServlet
{
String instanceMemberString = "Instance Member Variable"; // Violation.

public void service(ServletRequest req, ServletResponse res)throws IOException
   {
  
   }

}

Should be written as:

package com.rule;

import javax.servlet.GenericServlet;
import javax.servlet.ServletRequest;
import javax.servlet.ServletResponse;

class Avoid_using_instance_variables_in_Servlets extends GenericServlet
{
public void service(ServletRequest req, ServletResponse res)throws IOException
   {
String localVariableString = "Local Variable String"; // Correction.
   }
  
}

Reference:  Reference Not Available.

Rule 11: Do_not_declare_service_methods_synchronized

Severity:  Medium
Rule:  Declaring the service methods synchronized will cause performance issues for the servlet.
Reason:  Declaring the service methods synchronized will cause performance issues for the servlet.

Usage Example: 

package com.rule;

import java.io.IOException;

import javax.servlet.Servlet;
import javax.servlet.ServletException;
import javax.servlet.ServletRequest;
import javax.servlet.ServletResponse;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;

public class Do_not_declare_service_methods_synchronized_violation extends HttpServlet
{
protected synchronized void doPost(HttpServletRequest arg0, HttpServletResponse arg1) throws ServletException, IOException // VIOLATION
{
// implementation
}
}

abstract class Do_not_declare_service_methods_synchronized_violation_2 implements Servlet
{
public synchronized void service(ServletRequest arg0, ServletResponse arg1) throws ServletException, IOException // VIOLATION
{
}
}

Should be written as:

package com.rule;

import java.io.IOException;

import javax.servlet.Servlet;
import javax.servlet.ServletException;
import javax.servlet.ServletRequest;
import javax.servlet.ServletResponse;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;

public class Do_not_declare_service_methods_synchronized_correction extends HttpServlet
{
protected void doPost(HttpServletRequest arg0, HttpServletResponse arg1) throws ServletException, IOException // CORRECTION
{
// implementation
}
}

abstract class Do_not_declare_service_methods_synchronized_correction_2 implements Servlet
{
public void service(ServletRequest arg0, ServletResponse arg1) throws ServletException, IOException // CORRECTION
{
}
}

Reference:  http://www.javapractices.com/Topic111.cjp
http://www.chongluo.com/books/xml/jxslt/ch06_05.htm
http://www.unix.org.ua/orelly/java-ent/servlet/ch03_01.htm

Rule 12: Define_default_public_constructor_for_servlet

Severity:  Medium
Rule:  Always define a default constructor for servlets.
Reason:  Always define a default constructor for servlets.

Usage Example: 

package com.rule;

import javax.servlet.http.HttpServlet;

public class Define_default_public_constructor_for_servlet_violation extends HttpServlet // VIOLATION
{
protected Define_default_public_constructor_for_servlet()
{
}
}

Should be written as:

package com.rule;

import javax.servlet.http.HttpServlet;

public class Define_default_public_constructor_for_servlet_correction extends HttpServlet
{
public Define_default_public_constructor_for_servlet() // CORRECTOIN
{
}
}

Reference:  Reference Not Available.

Rule 13: Minimize_synchronization_in_servlets

Severity:  Medium
Rule:  Minimize the use of synchronized code in the servlets.
Reason:  Minimize the use of synchronized code in the servlets.

Usage Example: 

package com.rule;

import java.io.IOException;
import java.util.Enumeration;

import javax.servlet.ServletContext;
import javax.servlet.ServletException;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import javax.servlet.http.HttpSession;

public class Minimize_synchronization_in_servlets_violation extends HttpServlet
{
protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException
{
synchronized(this) // VIOLATION
{
Enumeration enum = request.getAttributeNames();
while(enum.hasMoreElements())
{
String attrName = (String) enum.nextElement();
doSomething(attrName);
}
HttpSession session = request.getSession();
session.setAttribute("attr1", "val1");
ServletContext servContext = session.getServletContext();
String info = servContext.getServerInfo();
response.getWriter().print(info);
}
}

private void doSomething(String obj)
{
}

}

Should be written as:

Minimize the code inside synchronized blocks.

Reference:  http://www-306.ibm.com/software/webservers/appserv/ws_bestpractices.pdf

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