关于这个报错，我们可能会遇到cannot be cast to（不能将什么类型转换成什么）我遇到问题的场景是在于复制包的时候没有导包。
applicationContext.xml如下
<?xml version="1.0" encoding="UTF-8"?><beans xmlns="/schema/beans"xmlns:xsi="/2001/XMLSchema-instance"xsi:schemaLocation="/schema/beans /schema/beans/spring-beans.xsd"><!-- 使用name属性实现构造注入--><bean id ="myStudent" class="com.bjpowernode.ba03.Student"><constructor-arg name="myname" value="张三"/><constructor-arg name="myage" value="20"/><constructor-arg name="mySchool" ref="myXuexiao"/></bean><!--声明School对象--><bean id="myXuexiao" class="com.bjpowernode.ba03.School"><property name="name" value="北京大学"/><property name="address" value="北京海淀区"/></bean>
School和Student如下
package com.bjpowernode.ba03;public class School {private String name;private String address;public void setName(String name) {this.name = name;}public void setAddress(String address) {this.address = address;}@Overridepublic String toString() {return "School{" +"name='" + name + ''' +", address='" + address + ''' +'}';}}package com.bjpowernode.ba03;public class Student {private String name;private int age;//声明一个引用类型private School school;public Student (){System.out.println("spring会调用类的无参构造器方法创建对象");}public void setName(String name) {this.name = name; }public void setSchool(School school) {this.school = school; }public void setAge(int age) {this.age = age; }/*** 创建有参数构造方法*/public Student(String myname,int myage,School mySchool){System.out.println("Student有参数构造方法");//属性赋值this.name=myname;this.age=myage;this.school=mySchool;}@Overridepublic String toString() {return "Student{" +"name='" + name + ''' +", age=" + age +", school=" + school +'}';}}
Mytest03如下
package com.bjpowernode.ba01;import org.junit.Test;import org.springframework.context.ApplicationContext;import org.springframework.context.support.ClassPathXmlApplicationContext;public class Mytest03 {@Testpublic void test01(){//使用spring容器创建对象//1.指定spring配置文件的名称String config = "ba03/applicationContext.xml";//注意：该引号内的配置文件必须是resources下的全限定名称，否则会报错//2.创建表示spring容器的对象，ApplicatContext//ApplicationContext就是表示spring容器，通过容器获取对象//ClassPathXmlApplicationContext:表示从类路径中加载spring的配置文件ApplicationContext ac = new ClassPathXmlApplicationContext(config);//从容器中获取某个对象，你要调用对象方法//getBean("配置文件中的bean的id值")//从容器中获取Student对象Student myStudent = (Student) ac.getBean("myStudent");System.out.println("student对象"+myStudent);}}
当Mytest03执行时，会出现如下的错误
Student有参数构造方法
java.lang.ClassCastException: com.bjpowernode.ba03.Student cannot be cast to com.bjpowernode.ba01.Student
由“Student有参数构造方法”我们可以知道，配置文件创建了对象并且执行了，即问题不在配置文件和Student和School里面，那么问题只能在Mytest03里面。
解决方法导包（导入cannot be cast to 前面的包，即可）：
import com.bjpowernode.ba03.Student;
此时
Student有参数构造方法
student对象Student{name=‘张三’, age=20, school=School{name=‘北京大学’, address=‘北京海淀区’}}
Process finished with exit code 0
