Spring: 基于xml的构造方法注入

科技 08-20 来源：小心程序猿QAQ

注入方式

具体有3种注入方式：通过构造方法的 a.参数名称注入 b.参数下标注入 c.默认参数顺序注入

参数名称注入

School实体类

package com.example.pojo03;public class School {    private String name;    private String address;    @Override    public String toString() {        return "School{" +                "name='" + name + '\'' +                ", address='" + address + '\'' +                '}';    }    public School(String name, String address) {        this.name = name;        this.address = address;        System.out.println("School有参构造方法执行，实例对象被创建....");    }}

applicationContext.xml

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

测试

package com.example.test;import org.junit.Test;import org.springframework.context.ApplicationContext;import org.springframework.context.support.ClassPathXmlApplicationContext;public class TestConstructor {    //测试：通过构造方法的参数名称注入    @Test    public void testConstructorArgs(){        //创建Spring容器        ApplicationContext ac = new ClassPathXmlApplicationContext("source03/applicationContext.xml");        //取出School对象并打印输出        System.out.printf("School实例对象: " + ac.getBean("school"));    }}

测试结果

School有参构造方法执行，实例对象被创建....School实例对象: School{name='nefu', address='哈尔滨'}Process finished with exit code 0

参数下标注入

实体类：新增Student实体类，持有School实例对象的引用

package com.example.pojo03;public class Student {    private String name;    private int age;    private School school;    @Override    public String toString() {        return "Student{" +                "name='" + name + '\'' +                ", age=" + age +                ", school=" + school +                '}';    }    public Student(String name, int age, School school) {        this.name = name;        this.age = age;        this.school = school;        System.out.println("Student有参构造方法执行，实例对象被创建....");    }}

applicationContext.xml：新增bean标签，注册Student实例对象

测试：新增测试方法

//测试：通过构造方法的参数下标注入    @Test    public void testConstructorIndex(){        //创建Spring容器        ApplicationContext ac = new ClassPathXmlApplicationContext("source03/applicationContext.xml");        //取出Student对象并打印输出        System.out.printf("Student实例对象: " + ac.getBean("student"));    }

测试结果

School有参构造方法执行，实例对象被创建....Student有参构造方法执行，实例对象被创建....Student实例对象: Student{name='荷包蛋', age=20, school=School{name='nefu', address='哈尔滨'}}Process finished with exit code 0

默认参数顺序注入

applicationContext.xml：新增bean标签，通过构造方法默认参数顺序注册Student实例对象，注意将之前对Student实例对象的注册先注释掉

测试：新增测试方法

//测试：通过构造方法默认参数顺序注入    @Test    public void testConstructorDefaultOrder(){        //创建Spring容器        ApplicationContext ac = new ClassPathXmlApplicationContext("source03/applicationContext.xml");        //取出Student对象并打印输出        System.out.printf("Student实例对象: " + ac.getBean("student02"));    }

测试结果

School有参构造方法执行，实例对象被创建....Student有参构造方法执行，实例对象被创建....Student实例对象: Student{name='荷包蛋', age=20, school=School{name='nefu', address='哈尔滨'}}Process finished with exit code 0