Spring 引导不注入 Bean 与 web 感知 scope

Question

If I try to inject a bean with a web aware scope (ie session scope, request scope), the injector ignores the bean. The bean method and object constructor are not called. This only happens for classes I have declared, as I can inject a session scoped bean for standard library types such as List or Map. In addition, injection works fine if I use singleton or prototype scopes.

Can someone explain this strange behavior? I created a barebones sample to demonstrate the issue. (I also tried searching, but couldn't find anyone who had this issue.)

Class I'd like to inject

public class CustomObj{
    public String field;

    public CustomObj(){
        System.out.println("CustomObj constructor called");
    }
}

Configuration file

@Configuration
public class Config {

    @Bean
    @Scope(value = WebApplicationContext.SCOPE_SESSION, proxyMode = ScopedProxyMode.TARGET_CLASS)
    public List<String> userValues() {
        List<String> list = new ArrayList<String>();
        list.add("This gets initialized");
        return list;
    }

    @Bean
    @Scope(value = WebApplicationContext.SCOPE_SESSION, proxyMode = ScopedProxyMode.TARGET_CLASS)
    public CustomObj customObj() {
        CustomObj obj = new CustomObj();
        obj.field = "This doesn't";
        return obj;
    }
}

Controller to inject the objects

@RestController
@RequestMapping("/test")
public class TestController{

    @Autowired
    List<String> userValues;

    @Autowired
    CustomObj customObj;

    @RequestMapping("/pleasework")
    public String please(){
        return "List values: "+Arrays.toString(this.userValues.toArray())
            + " Obj value: "+this.customObj.field;
    }
}

Main

@SpringBootApplication
public class SessionbeansApplication {

    public static void main(String[] args) {
        SpringApplication.run(SessionbeansApplication.class, args);
    }

}

Accessing /test/pleasework gives output List values: [This gets initialized] Obj value: null , showing that the List is injected properly but CustomObj is not.

Answer 1

If you run your code the output will be like List values: [This gets initialized] Obj value: null

You are NOT getting a NullpoiterException , this means that your CustomObj-bean is created

You should use getters and setter in your CustomObj. And use getter to access field: this.customObj.getField();

    @RequestMapping("/pleasework")
    public String please(){
        System.out.println(userValues +  " and " + customObj);
        return "List values: "+ Arrays.toString(this.userValues.toArray())
                + " Obj value: " + this.customObj.getField();// <--- use getter
    }

adding toString() in CustomObj will work also

class CustomObj {
    public String field;

    public CustomObj(){
        System.out.println("CustomObj constructor called");
    }

    @Override
    public String toString() {
        return "CustomObj{" +
                "field='" + field + '\'' +
                '}';
    }
}

....

  @RequestMapping("/pleasework")
    public String please(){
        System.out.println(userValues +  " and " + customObj);
        return "List values: "+ Arrays.toString(this.userValues.toArray())
                + " Obj value: " + this.customObj; //<---- use toString()
    }