Spring control inversion and dependency Injection

 

 

The environment used: dom4j spring 2.5.6, with: Spring. Jar dom4j. Jar common-logging.jar

Unit tests were performed on applications using Junit-4. And adopts interface-oriented programming (Abstract The interface layer)

 

Spring configuration file: Beans. xml

 

<? 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-2.5.xsd">
<! -- Instantiate the bean to implement control inversion, that is, the spirng container is responsible for creating objects -->
<Bean id = "personservice" class = "com. SGL. Imp. personservicebean"> </bean>

<! -- Perform dependency injection using the set method -->

<Bean id = "daoPerson" class = "com. sgl. dao. imp. PersonDaoBean"> </bean>
<Bean id = "personService4" class = "com. sgl. imp. PersonServiceBean">
<Property name = "personDao" ref = "daoPerson"> </property>
</Bean>

</Beans>

 

The source java files used are as follows:

1. Custom Application context (CORE)

Package sgl. spring. principle;

Import java. beans. Introspector;
Import java. beans. PropertyDescriptor;
Import java. lang. reflect. Method;
Import java.net. URL;
Import java. util. ArrayList;
Import java. util. HashMap;
Import java. util. List;
Import java. util. Map;
Import java. util. Logging. level;
Import java. util. Logging. Logger;
Import org. dom4j. Document;
Import org. dom4j. element;
Import org. dom4j. XPath;
Import org. dom4j. Io. saxreader;

/**
*
* @ Author Administrator
*/
Public class sglclasspathxmlapplicationcontext {

Private list <beandefinition> beandefines = new arraylist <beandefinition> (); // stores all bean instances
Private Map <string, Object> sinletons = new hashmap <string, Object> (); // stores the ing between bean and its associated class instances.

Public sglclasspathxmlapplicationcontext (string filename ){
This. readxml (filename );
This. instanceBeans ();
This. injectObject ();
}

/**
* Read the xml configuration file
* @ Param fileName configuration file name
*/
Private void readXml (String fileName ){
SAXReader saxReader = new SAXReader ();
Document document = null;

URL xmlPath = this. getClass (). getClassLoader (). getResource (fileName );
Try {
Document = saxReader. read (xmlPath );
Map <String, String> nsMap = new HashMap <String, String> ();
NsMap. put ("ns", "http://www.springframework.org/schema/beans"); // Add namespace
XPath xsub = document. createXPath ("// ns: beans/ns: bean"); // create/beans/bean query path
Xsub. setNamespaceURIs (nsMap); // you can specify a namespace.
List <Element> beans = xsub. selectNodes (document); // obtain all beans in the document

For (Element element: beans ){
String id = element. attributevalue ("ID"); // obtain the bean ID attribute
String classname = element. attributevalue ("class"); // obtain the class attribute of bean
XPath propertypath = element. createxpath ("ns: Property"); // create a bean/property query path
Propertypath. setnamespaceuris (nsmap); // set the namespace to be consistent with the root element.
List <element> propertys = propertypath. selectnodes (element); // obtain all properties under element (bean)

Beandefinition beandefine = new beandefinition (ID, classname); // instantiate a bean
// Set the property. because there may be multiple properties, use a loop
For (element property: propertys ){
String name = property. attributevalue ("name"); // obtain the name attribute of the property.
String ref = property. attributevalue ("Ref"); // obtain the ref attribute of the property.
System. out. println ("" + name + "" + ref );
PropertyDefinition propertyDefine = new PropertyDefinition (name, ref );
BeanDefine. getPropertys (). add (propertyDefine );
}
BeanDefines. add (beanDefine); // add the bean instance to the array
}

} Catch (Exception ex ){
Logger. getLogger (SglClassPathXmlApplicationContext. class. getName (). log (Level. SEVERE, null, ex );
}
}

/**
* Bean instantiation
*/
Private void instanceBeans (){
System. out. println ("Start of Instantiation ");
For (BeanDefinition beanDefine: beanDefines ){
If (beanDefine. getClassName ()! = Null &&! "". Equals (beanDefine. getClassName (). trim ())){
Try {
// Use java reflection technology to obtain java class instances
System. out. println ("beanID" + beanDefine. getId ());
Sinletons. put (beanDefine. getId (), Class. forName (beanDefine. getClassName (). newInstance ());
} Catch (Exception ex ){
Logger. getLogger (SglClassPathXmlApplicationContext. class. getName (). log (Level. SEVERE, null, ex );
}
}
}
System. out. println ("End of Instantiation ");
}

/**
* Retrieve bean instances
* @ Param beanName
* @ Return
*/
Public Object getBean (String beanName ){
Return this. sinletons. get (beanName );
}

Private void injectObject (){
For (beandefinition beandefine: beandefines) {// traverses all <beans>, because all <beans> can have the property attribute on the right.
Object bean = getbean (beandefine. GETID (); // obtain the bean instance id
If (bean! = NULL ){
Try {
// If the property retrieved from <property> (stored in the Name field) is in the property (FIELD) of the class corresponding to <bean>, we must ensure that
// <Property name = "property" ......> The "attribute" in has a corresponding definition in the class pointed to by <bean>

// Obtain the description of all attributes of the bean class (that is, all fields defined by the bean class)
PropertyDescriptor [] ps = Introspector. getBeanInfo (bean. getClass (). getPropertyDescriptors ();

For (PropertyDefinition property: beanDefine. getPropertys () {// a bean can have multiple <property>
// PropertyDescriptor contains many fields to find the fields corresponding to <property name = "property">
For (PropertyDescriptor propertyDes: ps) {// propertyDes is the description of the definition field pointed to by <bean>
System. out. println ("ps" + propertyDes. getName ());
// If the property name field is defined in <bean>, inject
If (property. getName (). equals (propertyDes. getName ())){
// Depending on the ref attribute in propety

// Obtain the property of the value corresponding to the name attribute of the property attribute of the current Bean class (here it refers to the persondao) setter Method
Method setter = propertydes. getwritemethod ();
// Obtain the corresponding ref class instance
If (setter! = NULL ){
Object value = sinletons. Get (property. getref ());
Setter. setaccessible (true); // make the private method transparent
Setter. Invoke (bean, value );
}

Break; // find the corresponding attribute. Do not compare other attributes.
}
}
}
} Catch (exception ex ){
Logger. getlogger (sglclasspathxmlapplicationcontext. Class. getname (). Log (level. Severe, null, ex );
}
}
}
}
}

 

2. PersonDao. java (Interface Program)

 

Package com. sgl. dao;
Public interface PersonDao {

Void add ();

}

 

3. PersonDaoBean. java (interface layer Implementation Program)
Package com. sgl. dao. imp;
Import com. sgl. dao. PersonDao;
Public class PersonDaoBean implements PersonDao {
Public void add (){
System. out. println ("execute the add () method in PersonDaoBean ");
}

}

4. PersonService. java (service layer interface)

Package com. sgl;
Public interface PersonService {

Void save ();

Void save2 ();

}

 

 

5. PersonServiceBean. java (business layer Implementation Program)

Package com. sgl. imp;
Import com. sgl. PersonService;
Import com. sgl. dao. PersonDao;

Public class PersonServiceBean implements PersonService {
Private PersonDao personDao;

Public void save (){
System. out. println ("I am the save () method in PersonServiceBean ");
PersonDao. add ();
}

 

Public void save2 (){
System. out. println ("this is the Save2 method in PersonServiceBean ");
}

Public void setPersonDao (PersonDao personDao ){
This. personDao = personDao;
}

}

 

6. In the configuration file, class encapsulation of corresponding properties (id, class, and property)

 

1) BeanDefinition. java

Package sgl. spring. principle;

Import java. util. ArrayList;
Import java. util. List;

Public class BeanDefinition {
Private String id;
Private String className;
Private List <PropertyDefinition> propertys = new ArrayList <PropertyDefinition> ();

Public BeanDefinition (){
}
Public BeanDefinition (String id, String className ){
This. id = id;
This. className = className;
}

Public String getId (){
Return id;
}

Public void setId (String id ){
This. id = id;
}

Public String getClassName (){
Return className;
}
Public void setClassName (String className ){
This. className = className;
}

Public List <PropertyDefinition> getPropertys (){
Return propertys;
}

Public void setpropertys (list <propertydefinition> propertys ){
This. propertys = propertys;
}
}

 

2) propertydefinition. Java (<property> definition)

Package SGL. Spring. principle;

Public class propertydefinition {
Private string name;
Private string ref;

Public propertydefinition (string name, string ref ){
This. Name = Name;
This. ref = ref;
}

Public propertydefinition (){
}

Public String getName (){
Return name;
}

Public void setName (String name ){
This. name = name;
}

Public String getRef (){
Return ref;
}

Public void setRef (String ref ){
This. ref = ref;
}

}

 

7. unit test file SglSpringTest. java, is a junit-4.x

 

 

Package junit. test;

Import com. sgl. PersonService;
Import org. junit. After;
Import org. junit. AfterClass;
Import org. junit. Before;
Import org. junit. BeforeClass;
Import org. junit. Test;
Import sgl. spring. principle. SglClassPathXmlApplicationContext;

Public class SglSpringTest {

Public SglSpringTest (){
}

@ BeforeClass
Public static void setUpClass () throws Exception {
}

@ AfterClass
Public static void tearDownClass () throws Exception {
}

@ Before
Public void setUp (){
}

@ After
Public void tearDown (){
}

@ Test
Public void instanceBeans (){
SglClassPathXmlApplicationContext ctx = new SglClassPathXmlApplicationContext ("beans. xml ");
// Test Control inversion, that is, the object created by the container
PersonService personService = (PersonService) ctx. getBean ("personService ");
PersonService. save2 ();
// Test Control reversal and dependency Injection
PersonService personService4 = (PersonService) ctx. getBean ("personService4 ");
PersonService4.save ();
}

}