错误原因：bean实例类中的属性类型与spring配置文件中的构造器属性类型不对应所导致，这种情况多出在使用类型指定构造器参数；
org.springframework.beans.factory.UnsatisfiedDependencyException: Error creating bean with name 'userId' defined in class path resource [com/java/f_xml/a_constructor/beans.xml]: Unsatisfied dependency expressed through constructor argument with index 0 of type [int]: Ambiguous constructor argument types - did you specify the correct bean references as constructor arguments?
Related cause: org.springframework.beans.factory.UnsatisfiedDependencyException: Error creating bean with name 'userId' defined in class path resource [com/java/f_xml/a_constructor/beans.xml]: Unsatisfied dependency expressed through constructor argument with index 1 of type [int]: Ambiguous constructor argument types - did you specify the correct bean references as constructor arguments?
这种错误是因为构造器中的type属性
不会自动对应拆箱装箱属性类型
，简单点说就是类中使用的是基本数据类型，配置文件中对应的type属性值就要是基本数据类型；类中使用的是类类型，配置文件中对应的type属性值就要是包名加上类类型；
public class User {
private String username;
private int id;//可以为private Integer id;对应的配置文件type="java.lang.Integer",返回数据库字段值是null的话，int类型会报错。int是基本数据类型，其声明的是变量，而null则是对象。所以建议用integer；
private int age;
public User(int id, int age) {
super();
this.id = id;
this.age = age;
}
public User(String username, int id) {
super();
this.username = username;
this.id = id;
}
}
xml:<bean id="userId" class="com.java.f_xml.a_constructor.User" >
<constructor-arg index="0" type=
"java.lang.String" value="jack"></constructor-arg>
<constructor-arg index="1" type=
"int" value="123"></constructor-arg>
</bean>
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