Let’s get started with Spring Bean !<\/p>\n\n\n\n\n\n\n\n
Bean is a key concept of the Spring Framework. Understanding this specific part of Spring Framework is crucial to use it efficiently.<\/p>\n\n\n\n
In this post, we will go throught this Spring concept.<\/p>\n\n\n\n
From the official Spring documentation :<\/p>\n\n\n\n
In Spring, the objects that form the backbone of your application and that are managed by the Spring IoC container are called beans. A bean is an object that is instantiated, assembled, and managed by a Spring IoC container. Otherwise, a bean is simply one of many objects in your application. Beans, and the dependencies among them, are reflected in the configuration metadata used by a container.<\/p><\/blockquote>\n\n\n\n
In Spring, bean is fully part of the IoC container, or “Inversion of Control” :<\/p>\n\n\n\n
It is a process whereby objects define their dependencies, that is, the other objects they work with, only through constructor arguments, arguments to a factory method, or properties that are set on the object instance after it is constructed or returned from a factory method. The container then injects<\/em> those dependencies when it creates the bean. This process is fundamentally the inverse, hence the name Inversion of Control<\/em> (IoC), of the bean itself controlling the instantiation or location of its dependencies by using direct construction of classes, or a mechanism such as the Service Locator<\/em> pattern.<\/p><\/blockquote>\n\n\n\n
The “Inversion of Control” process allows you to create instances, without creating them using the new<\/em> Java instruction.<\/p>\n\n\n\n
Java sample<\/h2>\n\n\n\n
In this post, we will use the following simple class :<\/p>\n\n\n\n
public class Person {\n \n private String firstName;\n\n private String lastName;\n\n private Address address;\n\n public Person() {\n\n }\n\n public Person(String firstName, String lastName, Address address) {\n setFirstName(firstName);\n setLastName(lastName);\n setAddress(address);\n }\n\n public String getFirstName() {\n return this.firstName;\n }\n\n public void setFirstName(String firstName) {\n this.firstName = firstName;\n }\n\n public String getLastName() {\n return this.lastName;\n }\n\n public void setFirstName(String lastName) {\n this.lastName = lastName;\n }\n\n public Address getAddress() {\n return this.address;\n }\n\n public void setAddress(Address address) {\n this.address= address;\n }\n}\n\npublic class Address {\n\n private String street;\n\n private int number;\n\n public Address() {\n\n }\n\n public Address(String street, int number) {\n setStreet(street);\n setNumber(number);\n }\n\n public String getStreet() {\n return this.street;\n }\n\n public void setStreet(String street) {\n this.street= street;\n }\n\n public int getNumber() {\n return this.number;\n }\n\n public void setNumber(int number) {\n this.number= number;\n }\n}<\/pre>\n\n\n\nJava way<\/h2>\n\n\n\n
In this example, we just want the following user :<\/p>\n\n\n\n
John Doe
123 Main St
Anytown, USA<\/p><\/blockquote>\n\n\n\nLet’s do this :<\/p>\n\n\n\n
Address address = new Address(\"Main St\", 123);\nPerson person = new Person(\"John\", \"Doe\", address);<\/pre>\n\n\n\nAs we can see in this approach, we are firstly creating the address <\/em>instance, and then pass it to the person <\/em>instance. Is there any alternative to do it ?<\/p>\n\n\n\n
Using Spring bean and the xml approach<\/h2>\n\n\n\n
We will use the following xml :<\/p>\n\n\n\n
<beans xmlns=\"http:\/\/springframework.org\/schema\/beans\"\n\txmlns:batch=\"http:\/\/springframework.org\/schema\/batch\" xmlns:task=\"springframework.org\/schema\/task\"\n\txmlns:util=\"http:\/\/springframework.org\/schema\/util\" xmlns:xsi=\"w3.org\/2001\/XMLSchema-instance\"\n\txsi:schemaLocation=\"http:\/\/springframework.org\/schema\/beans\n\t\thttp:\/\/springframework.org\/schema\/beans\/spring-beans-3.2.xsd\">\n\n <bean id=\"address\" class=\"my.package.Address\" \/>\n <property name=\"street\" value=\"Main St\" \/>\n <property name=\"number\" value=\"123\" \/>\n <\/bean>\n\n <bean id=\"person\" class=\"my.package.Person\" \/>\n <property name=\"firstName\" value=\"John\" \/>\n <property name=\"lastName\" value=\"Doe\" \/>\n <property name=\"address\" ref=\"address\" \/>\n <\/bean>\n<\/beans><\/pre>\n\n\n\nThe Java part :<\/p>\n\n\n\n
ApplicationContext ctx = new ClassPathXmlApplicationContext(\"beans.xml\");\nPerson person = ctx.getBean(\"person\", Person.class);<\/pre>\n\n\n\nThis xml file will produce, using the “Inversion of Control”, 2 beans. All beans are automatically created using the IoC, and can be retrieved using a getBean <\/em>call.<\/p>\n\n\n\n
Conclusion<\/h2>\n\n\n\n
Using Spring Bean, all instance declaration is moved from code to specific configuration file (or annotation). All objects are created by the Spring Framework, and can be retrieved independently.<\/p>\n\n\n\n
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