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This article focuses on "how to assign the @ Value attribute of Spring". Interested friends may wish to have a look at it. The method introduced in this paper is simple, fast and practical. Now let the editor take you to learn how to assign the @ Value attribute of Spring.

1. Create a new configuration class

Create a new configuration class. @ Configuration is designated as the configuration class, and @ Bean loads the Person class in preparation for the test. The code is as follows: @ Configurationpublic class MainConfigOfPropertyValues {@ Bean public Person person () {return new Person ();}

}

two。 Establish a new test method

Establish a test method to obtain and print the Bean of Person

Public class IOCTest_PropertyValue {AnnotationConfigApplicationContext applicationContext = new AnnotationConfigApplicationContext (MainConfigOfPropertyValues.class); @ Test public void test01 () {printBeans (applicationContext); System.out.println ("="); Person person = (Person) applicationContext.getBean ("person"); System.out.println (person);} private void printBeans (AnnotationConfigApplicationContext applicationContext) {String [] definitionNames = applicationContext.getBeanDefinitionNames () For (String name: definitionNames) {System.out.println (name);}}

} the test class runs as follows, and you can see that all the fields in the person Bean are empty by default. The assignment will be made below

3. Assign values through @ Value

Attributes can be assigned in xml configuration files by including property in the bean tag. @ Value can be used to assign attributes in annotation development. Where a value of 1. The basic data type @ Value ("Zhang San") private String name;2. You can write SpEL;# {}, that is, the expression @ Value ("# {20-2}") private Integer age;3 of sping. You can write ${}; take out the value in the configuration file [properties] (the value in the runtime environment variable)

@ Value ("${person.nickName}") private String nickName; runs as follows, which is assigned successfully

4. Load the configuration file through @ PropertySource and inject it

When you configure a xml file, you can introduce the configuration file through the context: property-placeholder tag. 1. In annotation development, you can use @ PropertySource to load the external configuration file @ PropertySource (value= {"classpath:/person.properties"}) 2. Create the properties file person.propertiesperson.nickName= Xiao Li IV to get the value of the configuration file through @ Value + ${}, or use the container's getEnvironment () method to call getProperty ("person.nickName"); get the contents of the configuration file. ConfigurableEnvironment environment = applicationContext.getEnvironment (); String property = environment.getProperty ("person.nickName"); System.out.println (property); add the test run results as follows:

5. Expand @ Value, @ PropertySource

@ Value static variable assignment

When dealing with static variables, the use of @ Value above cannot get the data in the configuration file, only null, so make the following changes.

The address of @ PropertySource annotation can be the following two:

Classpath path: "classpath:/com/myco/app.properties"

File corresponding path: "file:/path/to/file"

At this point, I believe you have a deeper understanding of "how to assign the @ Value attribute of Spring". You might as well do it in practice. Here is the website, more related content can enter the relevant channels to inquire, follow us, continue to learn!

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