spring
Configurazione ApplicationContext

Osservazioni

Configurazione Java

La configurazione Java viene in genere eseguita applicando l'annotazione @Configuration a una classe per suggerire che una classe contiene definizioni di bean. Le definizioni dei bean vengono specificate applicando l'annotazione @Bean a un metodo che restituisce un oggetto.

@Configuration // This annotation tells the ApplicationContext that this class
               // contains bean definitions.
class AppConfig {
    /**
     * An Author created with the default constructor
     * setting no properties
     */
    @Bean // This annotation marks a method that defines a bean 
    Author author1() {
        return new Author();
    }

    /**
     * An Author created with the constructor that initializes the 
     * name fields
     */
    @Bean
    Author author2() {
        return new Author("Steven", "King");
    }

    /**
     * An Author created with the default constructor, but  
     * then uses the property setters to specify name fields
     */
    @Bean
    Author author3() {
        Author author = new Author();
        author.setFirstName("George");
        author.setLastName("Martin");
        return author;
    }

    /**
     * A Book created referring to author2 (created above) via
     * a constructor argument.  The dependency is fulfilled by
     * invoking the method as plain Java.
     */
    @Bean
    Book book1() {
        return new Book(author2(), "It");
    }

    /**
     * A Book created referring to author3 (created above) via
     * a property setter.  The dependency is fulfilled by
     * invoking the method as plain Java.
     */
    @Bean
    Book book2() {
        Book book = new Book();
        book.setAuthor(author3());
        book.setTitle("A Game of Thrones");
        return book;
    }
}

// The classes that are being initialized and wired above...
class Book { // assume package org.springframework.example
    Author author;
    String title;
    
    Book() {} // default constructor
    Book(Author author, String title) {
        this.author = author;
        this.title= title;
    }

    Author getAuthor() { return author; }
    String getTitle() { return title; }

    void setAuthor(Author author) {
        this.author = author;
    }

    void setTitle(String title) {
        this.title= title;
    }
}

class Author { // assume package org.springframework.example
    String firstName;
    String lastName;

    Author() {} // default constructor
    Author(String firstName, String lastName) {
        this.firstName = firstName;
        this.lastName = lastName;
    }

    String getFirstName() { return firstName; }
    String getLastName() { return lastName; }

    void setFirstName(String firstName) {
        this.firstName = firstName;
    }

    void setLastName(String lastName) {
        this.lastName = lastName;
    }
}

Configurazione Xml

La configurazione Xml viene in genere eseguita definendo i bean all'interno di un file xml, utilizzando lo schema dei beans specifici di Spring. Sotto l'elemento dei beans radice, la definizione di bean tipica verrebbe eseguita utilizzando il sottoelemento del bean .

<?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">
    <!-- An Author created with the default constructor
         setting no properties -->
    <bean id="author1" class="org.springframework.example.Author" />
    
    <!-- An Author created with the constructor that initializes the 
         name fields -->
    <bean id="author2" class="org.springframework.example.Author">
        <constructor-arg index="0" value="Steven" />
        <constructor-arg index="1" value="King" />
    </bean>

    <!-- An Author created with the default constructor, but  
         then uses the property setters to specify name fields -->
    <bean id="author3" class="org.springframework.example.Author">
        <property name="firstName" value="George" />
        <property name="lastName" value="Martin" />
    </bean>

    <!-- A Book created referring to author2 (created above) via
         a constructor argument -->
    <bean id="book1" class="org.springframework.example.Book">
        <constructor-arg index="0" ref="author2" />
        <constructor-arg index="1" value="It" />
    </bean>

    <!-- A Book created referring to author3 (created above) via
         a property setter -->
    <bean id="book1" class="org.springframework.example.Book">
        <property name="author" ref="author3" />
        <property name="title" value="A Game of Thrones" />
    </bean>
</beans>

// The classes that are being initialized and wired above...
class Book { // assume package org.springframework.example
    Author author;
    String title;
    
    Book() {} // default constructor
    Book(Author author, String title) {
        this.author = author;
        this.title= title;
    }

    Author getAuthor() { return author; }
    String getTitle() { return title; }

    void setAuthor(Author author) {
        this.author = author;
    }

    void setTitle(String title) {
        this.title= title;
    }
}

class Author { // assume package org.springframework.example
    String firstName;
    String lastName;

    Author() {} // default constructor
    Author(String firstName, String lastName) {
        this.firstName = firstName;
        this.lastName = lastName;
    }

    String getFirstName() { return firstName; }
    String getLastName() { return lastName; }

    void setFirstName(String firstName) {
        this.firstName = firstName;
    }

    void setLastName(String lastName) {
        this.lastName = lastName;
    }
}

autowiring

L'autowiring viene eseguito utilizzando un'annotazione di sterotype per specificare quali classi saranno bean in ApplicationContext e utilizzando le annotazioni Autowired e Value per specificare le dipendenze del bean. La parte unica di autowiring è che non esiste una definizione ApplicationContext esterna, poiché viene eseguita interamente all'interno delle classi che sono i bean stessi.

@Component // The annotation that specifies to include this as a bean
           // in the ApplicationContext
class Book {
    
    @Autowired // The annotation that wires the below defined Author
               // instance into this bean
    Author author;

    String title = "It";

    Author getAuthor() { return author; }
    String getTitle() { return title; }
}

@Component // The annotation that specifies to include
           // this as a bean in the ApplicationContext
class Author {
    String firstName = "Steven";
    String lastName = "King";

    String getFirstName() { return firstName; }
    String getLastName() { return lastName; }
}

Avvio automatico di ApplicationContext

Java Config

La classe di configurazione deve essere solo una classe che si trova sul classpath dell'applicazione e visibile alla classe principale delle applicazioni.

class MyApp {
    public static void main(String[] args) throws Exception {
        AnnotationConfigApplicationContext appContext =
            new AnnotationConfigApplicationContext(MyConfig.class);
        
        // ready to retrieve beans from appContext, such as myObject.
    }
}

@Configuration
class MyConfig {
    @Bean
    MyObject myObject() {
        // ...configure myObject...
    }

    // ...define more beans...
}

Xml Config

Il file di configurazione xml deve essere solo sul classpath dell'applicazione.

class MyApp {
    public static void main(String[] args) throws Exception {
        ClassPathXmlApplicationContext appContext =
            new ClassPathXmlApplicationContext("applicationContext.xml");
        
        // ready to retrieve beans from appContext, such as myObject.
    }
}

<?xml version="1.0" encoding="UTF-8"?>
<!-- applicationContext.xml -->
<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="myObject" class="com.example.MyObject">
        <!-- ...configure myObject... -->
    </bean>

    <!-- ...define more beans... -->
</beans>

autowiring

Autowiring ha bisogno di sapere quali pacchetti di base scansionare per i bean annotati ( @Component ). Questo è specificato tramite il #scan(String...) .

class MyApp {
    public static void main(String[] args) throws Exception {
        AnnotationConfigApplicationContext appContext =
            new AnnotationConfigApplicationContext();
        appContext.scan("com.example");
        appContext.refresh();
        
        // ready to retrieve beans from appContext, such as myObject.
    }
}

// assume this class is in the com.example package.
@Component
class MyObject {
    // ...myObject definition...
}