Java Singleton Pattern

Singleton pattern is the most common types of patterns used in Java. It is also very common that interviewers ask questions to explain and implement singleton pattern

Lets first define Singleton
Singleton is a class whose only one object can be created.
There are couple of ways to implement Singleton class. Lets see the simplest one first.

Java Collection Interview Questions

Java Interview Questions.

REST webservice using jax-rs

In the previous post of SOAP webservice using JAX-WS we explored how to host a SOAP webservice and test it using JAX-WS, here we will host a REST webservice.

SOAP spring-ws with username authentication security

Their are different ways to secure SOAP based webservices.
1. Username/Password
2. Timestamp
3. Encryption/ Decryption
4. Digital Signature

Among these the most common and easy type of security is username/password. This security is very similar to a web application having a login page at the start for Authentication.

Spring-ws provides API to do this kind of security.
Extending our example in the previous post to host a SOAP based webservice, here we apply username security

Following tag is needed to be added in *-servlet.xml.

<sws:interceptors>
  <bean
   class="org.springframework.ws.soap.server.endpoint.interceptor.PayloadValidatingInterceptor">
   <property name="schema" value="/WEB-INF/login.xsd" />
   <property name="validateRequest" value="true" />
   <property name="validateResponse" value="true" />
  </bean>
  <bean
   class="org.springframework.ws.server.endpoint.interceptor.PayloadLoggingInterceptor">
  </bean>
  <bean
   class="org.springframework.ws.soap.security.xwss.XwsSecurityInterceptor">
   <property name="policyConfiguration" value="/WEB-INF/securityPolicy.xml" />
   <property name="callbackHandlers">
    <list>

    <!--  <ref bean="keyStoreHandler" /> -->
     <ref bean="callbackHandler" />
     
    </list>
   </property>
 </bean>
 </sws:interceptors>
 <bean id="callbackHandler"
  class="org.springframework.ws.soap.security.xwss.callback.SimplePasswordValidationCallbackHandler">
  <property name="users">
   <props>
    <prop key="admin">secret</prop>
    <prop key="clinetUser">pass</prop>
   </props>
  </property>
 </bean>

Here XwsSecurityInterceptor is used as a interceptor to apply security. The Interceptor refers securityPolicy.xml mentioned below to apply security. The additional parameters used for security are mentioned in the callbackHandler bean tag.

securityPolicy.xml
The securityPolicy.xml below mentions that the request to the service should contain username/password parameters. If not then the response would be a FAULT

<xwss:SecurityConfiguration xmlns:xwss="http://java.sun.com/xml/ns/xwss/config">

 <xwss:RequireUsernameToken
  passwordDigestRequired="true" nonceRequired="true" />

</xwss:SecurityConfiguration>

Once deployed the service can be tested using SOAP UI. The complete description is provided here.

For Web Service Introduction click here

Below are some posts that explain how to implement and test SOAP/REST Webservices

Host
SOAP	REST
JAX-WS	JAX-RS
Spring-ws	Spring-MVC-REST
Client
SOAP	REST
JAX-WS(wsimport)	Google REST APP
SOAP UI	Apache REST