【Spring】 No qualifying bean of type ‘java.lang.String‘ available: expected at least 1 bean which qua

1、问题所在

在使用spring框架中controller依赖user实体类，重载了其默认的构造方法。重载之后 默认的构造方法就会被覆盖。

@Controller
@RequestMapping(value="/user")
public class HelloController{
	@Resource
	private User user;

	@RequestMapping(value="/hello")
	public ModelAndView hello() {
		System.out.println("Hello,Annotation Spring MVC!");	
		user.setName("abc");
		System.out.print(user.getName());
		ModelAndView mv=new ModelAndView();
		mv.addObject("msg","ccc");
		mv.setViewName("first");
		return mv;
	}
}

@Component(value = "user")
public class User {
	private String name;
	private String password;
	

	public User(String name, String password) {
		this.name = name;
		this.password = password;
	}
	//省略set,get方法
}

2、出现的错误

Caused by: org.springframework.beans.factory.NoSuchBeanDefinitionException: No qualifying bean of type 'java.lang.String' available: expected at least 1 bean which qualifies as autowire candidate. Dependency annotations: 

3、分析错误

原因是springioc容器加载bean默认使用无参构造进行初始化。这里我们可以看到提示显示的是没有找到NoSuchBeanDefinition ，就是因为没有定义user的默认构造方法！！！

注意：
spring实例化bean对象，默认是无参构造方法实例化的，这时就需要bean类中存在无参构造方法。