Explain the example + detail the difference between @Resource and @Autowired annotations (the most complete in the entire network)

前言
1、什么是byName和byType
简单来说,byNameIt is to match according to the variable namebean的id属性,而byTypeIt is matched according to the variable typebean的class属性.实例说明：

<bean id="userService" class="com.test.UserServiceImpl"></bean> 
@Autowired
private UserService userService;

此处byNameJust take the variable nameuserService去匹配IOC容器的id为userService的bean,而byTypeJust take the variable typeUserService去匹配IOC容器的id为com.test.UserService.UserServiceImpl的bean,Here can be matched successfully becauseUserServiceImpl是UserService的实现类.

2、@Resource与@Autowired都是用来自动装配bean的.

一、@Resource
1、java中自带的注解 (javax.annotation.Resource)
2、默认按照名称(byName)方式进行bean装配,也可以按类型(byType)装配　
3、@Resource的作用范围：类、成员变量、方法
4、@Resource的使用
步骤：@Resource默认通过byName注入,如果没有匹配则通过byType注入.

@Service
public class UserServiceImpl1 implements UserService

@Service
public class UserServiceImpl2 implements UserService

@Resource
private UserService userService;

First pass by defaultbyName匹配,变量名userService无法匹配IOCany of the containersid（因为这里UserService有两个实现类,There are corresponding twobean,即userServiceImpl1和userServiceImpl2）,于是再通过byType匹配,发现类型UserServiceThe implementation classes are two,仍然无法确定,于是报错.
It will be mentioned at this [email protected]两个重要的属性：name和type,They are used to specify explicitlybyName和byType方式.
Displays the designation to match thatbean时,主要有以下四种情况：

// 1. 默认方式：byName That is, the designation is not displayed
@Resource  
private UserService userDao; 

// 2. 显示指定byName
@Resource(name="userService")  
private UserService userService; 

// 3. 显示指定byType
@Resource(type=UserService.class)  
private UserService userService; 

// 4. 显示指定byName和byType
@Resource(name="userService",type=UserService.class)  
private UserService userService; 

①既没指定name属性,也没指定type属性：默认通过byName方式注入,如果byName匹配失败,则使用byType方式注入（That is the example above）
②指定name属性：通过byName方式注入,Put the variable name and IOC容器中的id去匹配,If the match fails, an error will be reported
③指定type属性：通过byType方式注入,在IOCMatches the corresponding type in the container,If there is no match or if more than one match is found, an error will be reported
④同时指定name属性和type属性：在IOC容器中匹配,A match for both name and type succeeds,Otherwise, an error will be reported.

二、@Autowired
1、Spring自带的注解(org.springframework.beans.factory.annotation.Autowired)
2、默认按照类型(byType)方式进行bean装配,Also by name(byName)装配,需要结合@Qualifier如：@Autowired @Qualifier("manImpl")
3、Assembled by defaultbean对象必须在IOC容器中存在,If it does not exist, an error will be reported but normal use will not be affected;若允许bean对象不存在,可设置@Autowired(required = false) .That is to say, ignore the current injectionbean,如果有直接注入,没有则跳过,也不会报错了
4、@Autowired的作用范围：成员变量、构造器、方法、参数、注解
5、@Autowired的使用
步骤：@Autowird默认的注入方式为byType,也就是根据类型匹配,当有多个实现时,则通过byName注入,也可以通过配合@Qualifier注解来显式指定name值,指明要使用哪个具体的实现类.

@Service
public class UserServiceImpl1 implements UserService

@Service
public class UserServiceImpl2 implements UserService

@Autowired
private UserService userService;

根据上面的步骤,can be easily judged,Using this directly will result in an error.
原因：首先通过byType注入,判断UserServiceTypes have two implementations,Can't be sure which one it is,于是通过byName方式,这里的变量名userService也无法匹配IOC容器中id（referred to hereuserServiceImpl1和userServiceImpl2）,于是报错.
（注意：通过注解注入到IOC容器的idThe value defaults to its class name in lower case,比如上面的UserServiceImpl1和UserServiceImpl2类bean的id默认为userServiceImpl1和userServiceImpl2）

解决方案：

// 方式一：改变变量名
//将原来的userservice改名为userServiceImpl1,This will match the corresponding uniquebean了
@Autowired
private UserService userServiceImpl1;

// 方式二：配合@Qualifier注解来显式指定name值,This will match the corresponding uniquebean了
@Autowired
@Qualifier(value = "userServiceImpl2")
private UserService userService;

// 方式三：配合@Primaryannotation to specify which one to autowirebean
//加上@Primary,匹配bean时,该beanwill be selected first.
@Service
@Primary
public class UserServiceImpl1 implements UserService

三、总结
1、@Resource与@Autowired对比

2、@Autowired装配流程

3、@Resource装配流程