Spring basics

Spring - Basics (refreshing the basics)

This scrap note includes: 

• Configuring beans using @Configuration
• Creating beans and referencing them
• Bean scopes

Configuring beans using @Configuration

You can configure actions such as configuring all the beans, reading resources from the property files, establishing connection to database in the @Configuration class.

@Configuration

@ComponentScan(basePackages = "com.deiveehan")

@PropertySource(value = "classpath:application.properties")

public class ApplicationConfig {

  @Inject

  Environment environment;

  @Bean

  public InternalResourceViewResolver configureInternalResourceViewResolver() {

    InternalResourceViewResolver resolver = new InternalResourceViewResolver();

    resolver.setPrefix("/WEB-INF/views/");

    resolver.setSuffix(".jsp");

    return resolver;

  }

}

Note: 

• @Configuration is used to tell that this is a Bean configuration file. 
• @ComponentScan is used to tell the container where to look for the class files. 
• @PropertySource is used to define the properties file. 
• environment.getProperty("host”) is used to get the property value. 
• @Bean is used to define the beans. 

Creating beans and referencing them

You can create beans in 2 ways - using xml or using bean configuration files. 

Using annotation: 

@Bean is used to define a bean and 

Referencing beans: 

@Autowired is used to reference a bean

You can autowire a bean at the class level and at the method level. 

Example: 

@Configuration

@EnableMongoRepositories(basePackages = {

"com.deivee.framework.mongorepository",

“com.deivee.app.mongorepository" })

public class MongoDBConfig {

@Autowired

Environment environment;

@Bean

public Mongo mongo() throws Exception {

  return new Mongo(environment.getProperty("host"));

}

@Bean

public MongoTemplate mongoTemplate() throws Exception {

  return new MongoTemplate(mongo(),

  environment.getProperty("mongoDBName"));

}

}

and the MongoTemplate can be accessed in any bean class as below

@Autowired MongoTemplate. 

Bean scopes

There are 5 different types of bean scopes in Spring

• singleton (single bean instance per container)
• prototype (new bean each time when referred)
• request (new bean for each request) 
• session (available for the entire session)
• globalsession (for a global http session, valid for portal application). 

For example you can create the scope for the bean when you create it. 

@Component

@Scope("prototype")

public class LoginAction {

Misc: 

• You can use @PostConstruct to perform action after it is constructed and use @PreDestroy to perform action before it is destroyed. 
• You can use @Profile to create profiles for different environment. 
• You can detect the type of device that is sending the request using this String userAgent = request.getHeader("User-Agent”); the value of userAgent will be android, iPad, kindle etc., 
• You can also use spring with other web frameworks such as JSF.