Spring构造函数依赖项注入-带vs.不带自动装配 [英] Spring constructor dependency injection - with vs. without autowired
问题描述
我遇到了中描述的问题这个问题，我已经通过在构造函数中添加@Autowired注释解决了这个问题.现在，我想知道为什么会有所帮助.
I had encountered a problem described in this question, which I've already resolved by adding @Autowired annotation to constructor. Now I wonder, why it helped. What is a difference between
public RegistrationController(UserDao userDao) {
this.userDao = userDao;
}
和
@Autowired
public RegistrationController(UserDao userDao) {
this.userDao = userDao;
}
在两种情况下，都将userDao注入Controller.我发现的唯一区别是，仅在第二个示例中，使用@persistenceContext注释标记的entityManager仅注入到userDao中.但是我不知道为什么.有什么线索吗?还有其他区别吗?
In both cases, userDao is injected to Controller. Only difference I discovered is that entityManager tagged with @persistenceContext annotation is injected into userDao only in the second example. But I don't know why. Any clues? And is there any other differences?
我的servlet上下文如下:
my servlet context looks like this:
<beans xmlns="http://www.springframework.org/schema/beans"
xmlns:context="http://www.springframework.org/schema/context"
xmlns:mvc="http://www.springframework.org/schema/mvc"
xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xmlns:p="http://www.springframework.org/schema/p"
xmlns:tx="http://www.springframework.org/schema/tx"
xsi:schemaLocation="
http://www.springframework.org/schema/beans http://www.springframework.org/schema/beans/spring-beans.xsd
http://www.springframework.org/schema/context http://www.springframework.org/schema/context/spring-context.xsd
http://www.springframework.org/schema/mvc http://www.springframework.org/schema/mvc/spring-mvc.xsd
http://www.springframework.org/schema/tx http://www.springframework.org/schema/tx/spring-tx.xsd">
<!--
Adds some default beans (HandlerAdapter, HandlerMapping, Binding Initializer...). It also turn on some annotations.
Explanation in https://stackoverflow.com/questions/28851306/spring-framework-what-is-the-purpose-of-mvcannotation-driven
WITHOUT THIS, @RequestMapping ANNOTATIONS ARE LOADED, BUT MAPPING DO NOT WORK!!
-->
<mvc:annotation-driven />
<!-- Set loading annotations from classes
<context:component-scan base-package="com.fido.pia"/>-->
<!--manual homepage-->
<mvc:view-controller path="/" view-name="home"/>
<!--view resolver-->
<bean class="org.springframework.web.servlet.view.InternalResourceViewResolver">
<property name="prefix" value="/WEB-INF/view/" />
<property name="suffix" value=".jsp" />
</bean>
<!--static resources - request will be handeled by ResourceHttpRequestHandler-->
<mvc:resources mapping="/resources/**" location="/resources/" />
<!--database config-->
<bean id="dataSource" class="org.springframework.jdbc.datasource.DriverManagerDataSource">
<property name="driverClassName" value="com.mysql.jdbc.Driver" />
<property name="url" value="jdbc:mysql://localhost:3306/pia" />
<property name="username" value="root" />
<property name="password" value="" />
</bean>
<!--entity manager factory-->
<bean id="entityManagerFactory" class="org.springframework.orm.jpa.LocalContainerEntityManagerFactoryBean">
<property name="packagesToScan" value="com.fido.pia.*/**" />
<property name="dataSource" ref="dataSource" />
<property name="jpaVendorAdapter">
<bean class="org.springframework.orm.jpa.vendor.HibernateJpaVendorAdapter">
<!--<property name="generateDdl" value="true" />-->
<property name="showSql" value="true" />
</bean>
</property>
</bean>
<!-- Transactions -->
<bean id="transactionManager" class="org.springframework.orm.jpa.JpaTransactionManager">
<property name="entityManagerFactory" ref="entityManagerFactory" />
</bean>
<!-- enable the configuration of transactional behavior based on annotations -->
<tx:annotation-driven transaction-manager="transactionManager" />
<!--Set loading annotations from classes-->
<context:component-scan base-package="com.fido.pia"/>
</beans>
控制器:
package com.fido.pia;
import com.fido.pia.dao.UserDao;
import com.fido.pia.model.User;
import java.io.IOException;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.stereotype.Controller;
import org.springframework.transaction.annotation.Transactional;
import org.springframework.web.bind.annotation.RequestMapping;
import org.springframework.web.bind.annotation.RequestMethod;
@Controller
@RequestMapping("/register")
public class RegistrationController {
private UserDao userDao;
@Autowired
public RegistrationController(UserDao userDao) {
this.userDao = userDao;
}
@RequestMapping(method = RequestMethod.POST)
@Transactional
public void registrationSubmit(HttpServletRequest request, HttpServletResponse response)
throws IOException{
String username = request.getParameter("first_name");
userDao.save(new User("test"));
response.sendRedirect("/");
}
}
道:
package com.fido.pia.dao;
import com.fido.pia.model.User;
import javax.persistence.EntityManager;
import javax.persistence.PersistenceContext;
import javax.persistence.PersistenceContextType;
import org.springframework.stereotype.Component;
import org.springframework.stereotype.Repository;
@Repository
public class UserDao {
@PersistenceContext
protected EntityManager entityManager;
public User save(User row) {
if(row.isNew()) {
entityManager.persist(row);
return row;
} else {
return entityManager.merge(row);
}
}
}
推荐答案
存在两种用于大多数对象注入的形式！
Exist two forms for injection most use of the objects!
- First
@Autowired,
- Second in constructor
@Autowired
constructor(Object object)
- other
@Autowired
setObjectMehod(Object object)
为两个以上的对象实现接口时，有必要限定要插入的对象.
When an interface is implemented for more than two objects, it is necessary to qualify the object to be inserted.
总是将每个要注入到组件中的对象，最常见的@ Repository，@ Services，@ Controller和@Component都具有适当的范围.
Always every object that is to be injected into a component, the most common @Repository, @Services, @Controller and @Component each with its proper scope.
注入具有相同的目的，只是对象所需要的方式和需求不同
Injections have the same purpose are only different ways and needs as needed by the object
这篇关于Spring构造函数依赖项注入-带vs.不带自动装配的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！
