（四）Spring从入门到入土——依赖注入（DI）

• 依赖注入（DI）
• 依赖：指Bean对象的创建依赖于容器。Bean对象的依赖资源
• 注入：指Bean对象

一共有三种：分别是构造器注入；Set注入；P命名和C命名注入

在Spring从入门到入土——快速上手Spring中Beans.xml中有详细介绍，即通过有参构造来创建

<?xml version="1.0" encoding="UTF-8"?>

​ 要求被注入的属性必须有set方法，set方法的方法名由set + 属性首字母大写 , 如果属性是boolean类型 , 没有set方法 , 是 is

Address.java

public class Address {
    private String Address;

    public String getAddress() {
 return Address;
    }

    public void setAddress(String address) {
 Address = address;
    }

    @Override
    public String toString() {
 return "Address{" +
  "Address='" + Address + ''' +
  '}';
    }
}

Student.java

public class Student {
    private String name;
    private Address address;
    private String[] books;
    private List hobbies;
    private Map card;
    private Set games;
    private String wife;
    private Properties info;

    public String getName() {
 return name;
    }

    public void setName(String name) {
 this.name = name;
    }

    public Address getAddress() {
 return address;
    }

    public void setAddress(Address address) {
 this.address = address;
    }

    public String[] getBooks() {
 return books;
    }

    public void setBooks(String[] books) {
 this.books = books;
    }

    public List getHobbies() {
 return hobbies;
    }

    public void setHobbies(List hobbies) {
 this.hobbies = hobbies;
    }

    public Map getCard() {
 return card;
    }

    public void setCard(Map card) {
 this.card = card;
    }

    public Set getGames() {
 return games;
    }

    public void setGames(Set games) {
 this.games = games;
    }

    public String getWife() {
 return wife;
    }

    public void setWife(String wife) {
 this.wife = wife;
    }

    public Properties getInfo() {
 return info;
    }

    public void setInfo(Properties info) {
 this.info = info;
    }

    @Override
    public String toString() {
 return "Student{" +
  "name='" + name + ''' +
  ", address=" + address.toString() +
  ", books=" + Arrays.toString(books) +
  ", hobbies=" + hobbies +
  ", card=" + card +
  ", games=" + games +
  ", wife='" + wife + ''' +
  ", info=" + info +
  '}';
    }
}

beans.xml

<?xml version="1.0" encoding="UTF-8"?>
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测试：

public class MyTest {
    public static void main(String[] args) {
      ApplicationContext context = new ClassPathXmlApplicationContext("beans.xml");
 Student student = (Student) context.getBean("student");
 System.out.println(student.toString());
    }
}

user.java：【注意，这里没有有参构造器】

public class User {
    private String name;
    private int age;

    public String getName() {
 return name;
    }

    public void setName(String name) {
 this.name = name;
    }

    public int getAge() {
 return age;
    }

    public void setAge(int age) {
 this.age = age;
    }

    @Override
    public String toString() {
 return "User{" +
  "name='" + name + ''' +
  ", age=" + age +
  '}';
    }
}

• 实体类中必须有set方法；
• 实体类中必须有无参构造器（默认存在）；
• 必须导入p命名空间注入方式依赖。

 导入约束 : xmlns:p="http://www.springframework.org/schema/p"
 
 
 

​ 就是构造器注入、需要在头文件下加入约束文件

 导入约束 : xmlns:c="http://www.springframework.org/schema/c"
 
 

> 此时会发现出问题：因为没有写有参构造函数

C命名空间注入就是所谓的构造器注入

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