Exploring Iterator Design Pattern

Intent
Provide a way to access the elements of an aggregate object sequentially without exposing its underlying representation

Applicability
1. To access an aggregate object's contents without exposing its internal representation.
2. To support multiple traversals of aggregate objects.
3. To provide a uniform interface for traversing different aggregate structures (support polymorphic iteration).

In this post, we will be dealing only with the External Iterators. A typical ExternalIterator interface is as such

package com.devfaqs.designpatterns;

public interface ExternalIterator<E>
{
    public boolean hasNext();
    public E next();
}

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Spring Framework - Autowiring a map, list or array using Annotation

You can auto-wire a particular property in spring, using @Autowired annotation. For using @Autowired annotation, you will have to register AutowiredAnnotationBeanPostProcessor bean instance in the spring IOC container

<bean class="org.springframework.beans.factory.annotation.AutowiredAnnotationBeanPostProcessor" />

OR
You can simply include the <context:annotation-config /> element in your bean configuration file. The <context:annotation-config /> automatically registers an instance of AutowiredAnnotationBeanPostProcessor for you

For including <context:annotation-config /> element, you need to include context namespace in the bean definition file

<beans xmlns="http://www.springframework.org/schema/beans"
  xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
  xmlns:context="http://www.springframework.org/schema/context"
  xsi:schemaLocation="http://www.springframework.org/schema/beans http://www.springframework.org/schema/beans/spring-beans-3.0.xsd 
  http://www.springframework.org/schema/context 
  http://www.springframework.org/schema/context/spring-context-3.0.xsd">

Auto wiring is supported for
1. Constructors
2. Setter Methods
3. Arbitrary Methods
4. Fields

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Advantages of Base64 Encoding

Base64 encoding is a technique used for converting binary data into blocks of printable ASCII characters. The Base64 encoding algorithm uses a special conversion table to assign one of the 64 ASCII characters to every 6 bits of the bytestream. That is to say, a binary stream is divided into blocks of six bits and each block is mapped to an ASCII character. The ASCII character with the value of 64 (character =) is used to signify the end of the binary stream.

Advantages
1. 7 Bit ASCII characters are safe for transmission over the network and between different systems
2. SMPT protocol for emails supports only 7 Bit ASCII Characters. Base64 is the commonly used technique to send binary files as attachments in emails.

Disadvantages
1. Base64 encoding bloats the size of the original binary stream by 33 percent
2. Encoding/Decoding process consumes resources and can cause performance problems

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Spring Framework - Injecting java properties

In this example we demonstrate how to inject Properties in our application.

The bean configuration file for injecting properties

<?xml version="1.0" encoding="UTF-8"?>
<beans xmlns="http://www.springframework.org/schema/beans"
  xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
  xsi:schemaLocation="http://www.springframework.org/schema/beans http://www.springframework.org/schema/beans/spring-beans.xsd">
  <bean id="databaseConnectionPool" class="com.examples.spring.SQLConnectionPool">
    <property name="properties">
        <props>
            <prop key="connections">5</prop>
            <prop key="timeout">3600</prop>
        </props>
    </property>
  </bean>
</beans>

The two properties are defined for the SQLConnectionPool class. These properties are injected using the setProperties setter method

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Spring Framework - Injecting a Map

In this example we will try to populate employees map using spring's setter injection.

Bean Configuration File

<?xml version="1.0" encoding="UTF-8"?>
<beans xmlns="http://www.springframework.org/schema/beans"
  xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
  xsi:schemaLocation="http://www.springframework.org/schema/beans http://www.springframework.org/schema/beans/spring-beans.xsd">
  <bean id="myCompany" class="com.examples.spring.Company">
    <property name="name" value="myWorld" />
    <property name="employees">
      <map>
        <entry>
          <key>
            <value>pankaj</value>
          </key>
          <bean class="com.examples.spring.Employee">
            <constructor-arg name="name" value="Pankaj Tiwari" />
          </bean>
        </entry>
        <entry>
          <key>
            <value>paresh</value>
          </key>
          <bean class="com.examples.spring.Employee">
            <constructor-arg name="name" value="Paresh Tiwari" />
          </bean>
        </entry>
        <entry>
          <key>
            <value>ankit</value>
          </key>
          <bean class="com.examples.spring.Employee">
            <constructor-arg name="name" value="Ankit Rawat" />
          </bean>
        </entry>
      </map>
    </property>
  </bean>
</beans>

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