Spring mvc @Value Notes

In the spring mvc architecture, if you want to use the configuration values ​​defined in properties directly in the program, you usually use the following methods to obtain:

    @Value("${tag}")
    private String tagValue;

 

But when taking the value, sometimes the tagvalue is NULL, the possible reasons are:

• The tagValue is modified with static or final, as follows:

    private static String tagValue;  //错误
    private final String tagValue;    //错误

• The class does not add @Component (or @service, etc.) Need to confirm whether the bean is loaded

    @Component   //遗漏
    class TestValue{
         @Value("${tag}")
         private String tagValue;
    }

• The class was created with a new instance without @Autowired

    @Component   
    class TestValue{
         @Value("${tag}")
         private String tagValue;
    }

    class Test{
        ...
        TestValue testValue = new TestValue()
    }

 

There is definitely no value in this testValue, you must use @Autowired:

Also pay attention to the imported package path: import org.springframework.beans.factory.annotation.Value;

I have encountered the copied code before, the package path introduces an error, no red cross is reported, but the value cannot be assigned.

class Test{
        @AutoWired
        TestValue testValue
    }