我们都知道，Spring框架的IOC是基于Java反射机制实现的，下面我们先回顾一下java反射。
1、回顾Java反射
Java反射机制是在运行状态中，对于任意一个类，都能够知道这个类的所有属性和方法；对于任意一个对象，都能够调用它的任意方法和属性；这种动态获取信息以及动态调用对象方法的功能称为Java语言的反射机制。简单来说，反射机制指的是程序在运行时能够获取自身的信息。
要想解剖一个类，必须先要获取到该类的Class对象。而剖析一个类或用反射解决具体的问题就是使用相关API（1）java.lang.Class（2）java.lang.reflect，所以，Class对象是反射的根源。
自定义类
代码语言：java复制package com.atguigu.reflect;
public class Car {
//属性
private String name;
private int age;
private String color;
//无参数构造
public Car() {
}
//有参数构造
public Car(String name, int age, String color) {
this.name = name;
this.age = age;
this.color = color;
}
//普通方法
private void run() {
System.out.println("私有方法-run.....");
}
//get和set方法
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;
}
public String getColor() {
return color;
}
public void setColor(String color) {
this.color = color;
}
@Override
public String toString() {
return "Car{"
"name='" name '''
", age=" age
", color='" color '''
'}';
}
}编写测试类
代码语言：java复制package com.atguigu.reflect;
import org.junit.jupiter.api.Test;
import java.lang.reflect.Constructor;
import java.lang.reflect.Field;
import java.lang.reflect.Method;
public class TestCar {
//1、获取Class对象多种方式
@Test
public void test01() throws Exception {
//1 类名.class
Class clazz1 = Car.class;
//2 对象.getClass()
Class clazz2 = new Car().getClass();
//3 Class.forName("全路径")
Class clazz3 = Class.forName("com.atguigu.reflect.Car");
//实例化
Car car = (Car)clazz3.getConstructor().newInstance();
System.out.println(car);
}
//2、获取构造方法
@Test
public void test02() throws Exception {
Class clazz = Car.class;
//获取所有构造
// getConstructors()获取所有public的构造方法
// Constructor[] constructors = clazz.getConstructors();
// getDeclaredConstructors()获取所有的构造方法public private
Constructor[] constructors = clazz.getDeclaredConstructors();
for (Constructor c:constructors) {
System.out.println("方法名称：" c.getName() " 参数个数：" c.getParameterCount());
}
//指定有参数构造创建对象
//1 构造public
// Constructor c1 = clazz.getConstructor(String.class, int.class, String.class);
// Car car1 = (Car)c1.newInstance("夏利", 10, "红色");
// System.out.println(car1);
//2 构造private
Constructor c2 = clazz.getDeclaredConstructor(String.class, int.class, String.class);
c2.setAccessible(true);
Car car2 = (Car)c2.newInstance("捷达", 15, "白色");
System.out.println(car2);
}
//3、获取属性
@Test
public void test03() throws Exception {
Class clazz = Car.class;
Car car = (Car)clazz.getDeclaredConstructor().newInstance();
//获取所有public属性
//Field[] fields = clazz.getFields();
//获取所有属性（包含私有属性）
Field[] fields = clazz.getDeclaredFields();
for (Field field:fields) {
if(field.getName().equals("name")) {
//设置允许访问
field.setAccessible(true);
field.set(car,"五菱宏光");
System.out.println(car);
}
System.out.println(field.getName());
}
}
//4、获取方法
@Test
public void test04() throws Exception {
Car car = new Car("奔驰",10,"黑色");
Class clazz = car.getClass();
//1 public方法
Method[] methods = clazz.getMethods();
for (Method m1:methods) {
//System.out.println(m1.getName());
//执行方法 toString
if(m1.getName().equals("toString")) {
String invoke = (String)m1.invoke(car);
//System.out.println("toString执行了：" invoke);
}
}
//2 private方法
Method[] methodsAll = clazz.getDeclaredMethods();
for (Method m:methodsAll) {
//执行方法 run
if(m.getName().equals("run")) {
m.setAccessible(true);
m.invoke(car);
}
}
}
}2、实现Spring的IoC
我们知道，IoC（控制反转）和DI（依赖注入）是Spring里面核心的东西，那么，我们如何自己手写出这样的代码呢？下面我们就一步一步写出Spring框架最核心的部分。
①搭建子模块
搭建模块：guigu-spring，搭建方式如其他spring子模块
②准备测试需要的bean
添加依赖
代码语言：html复制<dependencies>
<!--junit5测试-->
<dependency>
<groupId>org.junit.jupiter</groupId>
<artifactId>junit-jupiter-api</artifactId>
<version>5.3.1</version>
</dependency>
</dependencies>创建UserDao接口
代码语言：java复制package com.atguigu.spring6.test.dao;
public interface UserDao {
public void print();
}创建UserDaoImpl实现
代码语言：java复制package com.atguigu.spring6.test.dao.impl;
import com.atguigu.spring.dao.UserDao;
public class UserDaoImpl implements UserDao {
@Override
public void print() {
System.out.println("Dao层执行结束");
}
}创建UserService接口
代码语言：java复制package com.atguigu.spring6.test.service;
public interface UserService {
public void out();
}创建UserServiceImpl实现类
代码语言：java复制package com.atguigu.spring.test.service.impl;
import com.atguigu.spring.core.annotation.Bean;
import com.atguigu.spring.service.UserService;
@Bean
public class UserServiceImpl implements UserService {
// private UserDao userDao;
@Override
public void out() {
//userDao.print();
System.out.println("Service层执行结束");
}
}③定义注解
我们通过注解的形式加载bean与实现依赖注入
bean注解
代码语言：java复制package com.atguigu.spring.core.annotation;
import java.lang.annotation.ElementType;
import java.lang.annotation.Retention;
import java.lang.annotation.RetentionPolicy;
import java.lang.annotation.Target;
@Target(ElementType.TYPE)
@Retention(RetentionPolicy.RUNTIME)
public @interface Bean {
}依赖注入注解
代码语言：java复制package com.atguigu.spring.core.annotation;
import java.lang.annotation.ElementType;
import java.lang.annotation.Retention;
import java.lang.annotation.RetentionPolicy;
import java.lang.annotation.Target;
@Target({ElementType.FIELD})
@Retention(RetentionPolicy.RUNTIME)
public @interface Di {
}说明：上面两个注解可以随意取名
④定义bean容器接口
代码语言：java复制package com.atguigu.spring.core;
public interface ApplicationContext {
Object getBean(Class clazz);
}⑤编写注解bean容器接口实现
AnnotationApplicationContext基于注解扫描bean
代码语言：java复制package com.atguigu.spring.core;
import java.util.HashMap;
public class AnnotationApplicationContext implements ApplicationContext {
//存储bean的容器
private HashMap<Class, Object> beanFactory = new HashMap<>();
@Override
public Object getBean(Class clazz) {
return beanFactory.get(clazz);
}
/**
* 根据包扫描加载bean
* @param basePackage
*/
public AnnotationApplicationContext(String basePackage) {
}
}⑥编写扫描bean逻辑
我们通过构造方法传入包的base路径，扫描被@Bean注解的java对象，完整代码如下：
代码语言：java复制package com.atguigu.spring.core;
import com.atguigu.spring.core.annotation.Bean;
import java.io.File;
import java.util.HashMap;
public class AnnotationApplicationContext implements ApplicationContext {
//存储bean的容器
private HashMap<Class, Object> beanFactory = new HashMap<>();
private static String rootPath;
@Override
public Object getBean(Class clazz) {
return beanFactory.get(clazz);
}
/**
* 根据包扫描加载bean
* @param basePackage
*/
public AnnotationApplicationContext(String basePackage) {
try {
String packageDirName = basePackage.replaceAll("\.", "\\");
Enumeration<URL> dirs =Thread.currentThread().getContextClassLoader().getResources(packageDirName);
while (dirs.hasMoreElements()) {
URL url = dirs.nextElement();
String filePath = URLDecoder.decode(url.getFile(),"utf-8");
rootPath = filePath.substring(0, filePath.length()-packageDirName.length());
loadBean(new File(filePath));
}
} catch (Exception e) {
throw new RuntimeException(e);
}
}
private void loadBean(File fileParent) {
if (fileParent.isDirectory()) {
File[] childrenFiles = fileParent.listFiles();
if(childrenFiles == null || childrenFiles.length == 0){
return;
}
for (File child : childrenFiles) {
if (child.isDirectory()) {
//如果是个文件夹就继续调用该方法,使用了递归
loadBean(child);
} else {
//通过文件路径转变成全类名,第一步把绝对路径部分去掉
String pathWithClass = child.getAbsolutePath().substring(rootPath.length() - 1);
//选中class文件
if (pathWithClass.contains(".class")) {
// com.xinzhi.dao.UserDao
//去掉.class后缀，并且把 替换成 .
String fullName = pathWithClass.replaceAll("\\", ".").replace(".class", "");
try {
Class<?> aClass = Class.forName(fullName);
//把非接口的类实例化放在map中
if(!aClass.isInterface()){
Bean annotation = aClass.getAnnotation(Bean.class);
if(annotation != null){
Object instance = aClass.newInstance();
//判断一下有没有接口
if(aClass.getInterfaces().length > 0) {
//如果有接口把接口的class当成key，实例对象当成value
System.out.println("正在加载【" aClass.getInterfaces()[0] "】,实例对象是：" instance.getClass().getName());
beanFactory.put(aClass.getInterfaces()[0], instance);
}else{
//如果有接口把自己的class当成key，实例对象当成value
System.out.println("正在加载【" aClass.getName() "】,实例对象是：" instance.getClass().getName());
beanFactory.put(aClass, instance);
}
}
}
} catch (ClassNotFoundException | IllegalAccessException | InstantiationException e) {
e.printStackTrace();
}
}
}
}
}
}
}⑦java类标识Bean注解
代码语言：java复制@Bean
public class UserServiceImpl implements UserService@Bean
public class UserDaoImpl implements UserDao ⑧测试Bean加载
代码语言：java复制package com.atguigu.spring;
import com.atguigu.spring.core.AnnotationApplicationContext;
import com.atguigu.spring.core.ApplicationContext;
import com.atguigu.spring.test.service.UserService;
import org.junit.jupiter.api.Test;
public class SpringIocTest {
@Test
public void testIoc() {
ApplicationContext applicationContext = new AnnotationApplicationContext("com.atguigu.spring.test");
UserService userService = (UserService)applicationContext.getBean(UserService.class);
userService.out();
System.out.println("run success");
}
}控制台打印测试
⑨依赖注入
只要userDao.print();调用成功，说明就注入成功
代码语言：java复制package com.atguigu.spring.test.service.impl;
import com.atguigu.spring.core.annotation.Bean;
import com.atguigu.spring.core.annotation.Di;
import com.atguigu.spring.dao.UserDao;
import com.atguigu.spring.service.UserService;
@Bean
public class UserServiceImpl implements UserService {
@Di
private UserDao userDao;
@Override
public void out() {
userDao.print();
System.out.println("Service层执行结束");
}
}执行第八步：报错了，说明当前userDao是个空对象
⑩依赖注入实现
代码语言：java复制package com.atguigu.spring.core;
import com.atguigu.spring.core.annotation.Bean;
import com.atguigu.spring.core.annotation.Di;
import java.io.File;
import java.lang.reflect.Field;
import java.util.HashMap;
import java.util.Map;
public class AnnotationApplicationContext implements ApplicationContext {
//存储bean的容器
private HashMap<Class, Object> beanFactory = new HashMap<>();
private static String rootPath;
@Override
public Object getBean(Class clazz) {
return beanFactory.get(clazz);
}
/**
* 根据包扫描加载bean
* @param basePackage
*/
public AnnotationApplicationContext(String basePackage) {
try {
String packageDirName = basePackage.replaceAll("\.", "\\");
Enumeration<URL> dirs =Thread.currentThread().getContextClassLoader().getResources(packageDirName);
while (dirs.hasMoreElements()) {
URL url = dirs.nextElement();
String filePath = URLDecoder.decode(url.getFile(),"utf-8");
rootPath = filePath.substring(0, filePath.length()-packageDirName.length());
loadBean(new File(filePath));
}
} catch (Exception e) {
throw new RuntimeException(e);
}
//依赖注入
loadDi();
}
private void loadBean(File fileParent) {
if (fileParent.isDirectory()) {
File[] childrenFiles = fileParent.listFiles();
if(childrenFiles == null || childrenFiles.length == 0){
return;
}
for (File child : childrenFiles) {
if (child.isDirectory()) {
//如果是个文件夹就继续调用该方法,使用了递归
loadBean(child);
} else {
//通过文件路径转变成全类名,第一步把绝对路径部分去掉
String pathWithClass = child.getAbsolutePath().substring(rootPath.length() - 1);
//选中class文件
if (pathWithClass.contains(".class")) {
// com.xinzhi.dao.UserDao
//去掉.class后缀，并且把 替换成 .
String fullName = pathWithClass.replaceAll("\\", ".").replace(".class", "");
try {
Class<?> aClass = Class.forName(fullName);
//把非接口的类实例化放在map中
if(!aClass.isInterface()){
Bean annotation = aClass.getAnnotation(Bean.class);
if(annotation != null){
Object instance = aClass.newInstance();
//判断一下有没有接口
if(aClass.getInterfaces().length > 0) {
//如果有接口把接口的class当成key，实例对象当成value
System.out.println("正在加载【" aClass.getInterfaces()[0] "】,实例对象是：" instance.getClass().getName());
beanFactory.put(aClass.getInterfaces()[0], instance);
}else{
//如果有接口把自己的class当成key，实例对象当成value
System.out.println("正在加载【" aClass.getName() "】,实例对象是：" instance.getClass().getName());
beanFactory.put(aClass, instance);
}
}
}
} catch (ClassNotFoundException | IllegalAccessException | InstantiationException e) {
e.printStackTrace();
}
}
}
}
}
}
private void loadDi() {
for(Map.Entry<Class,Object> entry : beanFactory.entrySet()){
//就是咱们放在容器的对象
Object obj = entry.getValue();
Class<?> aClass = obj.getClass();
Field[] declaredFields = aClass.getDeclaredFields();
for (Field field : declaredFields){
Di annotation = field.getAnnotation(Di.class);
if( annotation != null ){
field.setAccessible(true);
try {
System.out.println("正在给【" obj.getClass().getName() "】属性【" field.getName() "】注入值【" beanFactory.get(field.getType()).getClass().getName() "】");
field.set(obj,beanFactory.get(field.getType()));
} catch (IllegalAccessException e) {
e.printStackTrace();
}
}
}
}
}
}执行第八步：执行成功，依赖注入成功
