Nattoise Labs: [Spring] 2 - Spring Quick Start

TOPIC

Application Classes Example with Configuration Instruction XML file
Compare with Constructor DI vs. Setter DI
Bean definition examples for Constructor DI and Setter DI
Bean definition examples for Setter DI with

values
static Factory Methods
instance Factory Methods

What is BeanFactory?
What is application context?
Create application context with multiple files
Bootstrapped in any environment

Spring quick start

Spring manages the lifecycle of the applicaiton

All beans are fully initialized before they are used ???

Beans are always created in the right order

Based on the dependencies
[Nattily] with <order>

Each bean is bound to a unique id

The id reflects the service the bean provides to clients

Spring encapsulates (~includes outside cannot see the details inside) the bean implementations chosen for a given application deployment.

Conceals(~hide) implementation details

Writing bean definitions

[Nattily] Write a bean configuration xml file can convert into Java code with unique bean id.
<bean> element

The root of the .xml file
The root element of any Spring configuration file

<bean> element

Tells the Spring container about the class and how it should be configured.

id attribute

takes the unique id

class attribute

specifies the bean's fully qualified class name

e.g. <bean id='glt0001' class ="com.hsbc.beans.SimpleBean">
<property> element

Tells the Spring container to call setName(), setStaffId() while setting the "name" and "staffId" property.

<value> element

Defines the value of "name" and "staffId" as "xyz" and "10551328"

The container instantiates the 'SimpleBean' based on the XML definition as:
Result:

SimpleBean glt001 = new SimpleBean();
glt001.setName("xyz");
glt001.setStaffId("10551328");

Types of Dependency Injection shown in coding

As discussed in last chapter, there are 2 types of Dependency Injection.

(1) Constructor Dependency Injection

Enforce mandatory dependencies
Promote immutability (cannot be changed forever)
Concise(~clear and simple) for programmatic usage

(2) Setter Dependency Injection

Have descriptive names
Follow JavaBean conventions
Inherited automatically

When to Use Constructors DI vs Setter DI?
Spring supports both
You can mix and match

General Recommendations

Follow standard Java Design guidelines

Use constructors to set required properties
Use setters for optional or those was default values

You may find some classes are designed for a particular injection strategy
Be consistent above all

Combining Constructor and Setter Dependency Injection

Injecting Scalar Values

Automatic Value Type Conversion

Calling Static Factory Methods

Q: A class can have both constructor and static method at the same time?

Calling Instance Factory Methods

Creating an application context

Spring application contexts can be bootstrapped in any environment, including

JUnit system test
Web application
Enterprise Java Bean (EJB)
Standalone application

Loadable with bean definitions from files:

In the class path
On the local file system
At an environment-relative resource path

[Nattily] 2 most fundamental packages:

org.springframework.beans packages
org.springframework.context packages

[Nattily] The ApplicationContext builds on top of the BeanFactory(it's a subclass).
[Nattily] The BeanFactory provides the configuration framework and basic functionality, while ApplicationContext added enhanced capabilities to it, some of them perhaps more J2EE and enterprise centric.

[Nattily] What is BeanFactory? [link]

The BeanFactory is the actual container which instantiates, configures, and manages a number of beans.
A BeanFactory is represented by the interface org.springframework.beans.factory.BeanFactory, for which there are multiple implementations.
the BeanFactory does have to be instantiated somehow.

Resource res = new FileSystemResource("beans.xml");
XmlBeanFactory factory = new XmlBeanFactory(res);

[Nattily] What is Application Context? [link]

ApplicationContext提供取得資源檔案更方便的方法。
ApplicationContext提供文字訊息解析的方法，並支援國際化（Internationalization, I18N）訊息。
ApplicationContext可以發佈事件，對事件感興趣的Bean可以接收到這些事件。

Create a Spring Application Context from Multiple Files

A context can be configured from multiple files
Allows partitioning of bean definitions into logical groups
Generally a best practice to separate out "application" beans from "infrastructure" beans