当前位置：首页 > news >正文

spring四种依赖注入方式

news 来源：原创 2024/5/5 23:32:36

2019独角兽企业重金招聘Python工程师标准>>>

平常的java开发中，程序员在某个类中需要依赖其它类的方法，则通常是new一个依赖类再调用类实例的方法，这种开发存在的问题是new的类实例不好统一管理，spring提出了依赖注入的思想，即依赖类不由程序员实例化，而是通过spring容器帮我们new指定实例并且将实例注入到需要该对象的类中。依赖注入的另一种说法是“控制反转”，通俗的理解是：平常我们new一个实例，这个实例的控制权是我们程序员，而控制反转是指new实例工作不由我们程序员来做而是交给spring容器来做。

spring有多种依赖注入的形式，下面仅介绍spring通过xml进行IOC配置的方式：

Set注入

这是最简单的注入方式，假设有一个SpringAction，类中需要实例化一个SpringDao对象，那么就可以定义一个private的SpringDao成员变量，然后创建SpringDao的set方法（这是ioc的注入入口）：

Java代码 <EMBED height=15 type=application/x-shockwave-flash pluginspage=http://www.macromedia.com/go/getflashplayer width=14 src=http://blessht.iteye.com/javascripts/syntaxhighlighter/clipboard_new.swf allowscriptaccess="always" quality="high" flashvars="clipboard=package%20com.bless.springdemo.action%3B%0Apublic%20class%20SpringAction%20%7B%0A%20%20%20%20%20%20%20%20%2F%2F%E6%B3%A8%E5%85%A5%E5%AF%B9%E8%B1%A1springDao%0A%09private%20SpringDao%20springDao%3B%0A%20%20%20%20%20%20%20%20%2F%2F%E4%B8%80%E5%AE%9A%E8%A6%81%E5%86%99%E8%A2%AB%E6%B3%A8%E5%85%A5%E5%AF%B9%E8%B1%A1%E7%9A%84set%E6%96%B9%E6%B3%95%0A%20%20%20%20%20%20%20%20public%20void%20setSpringDao(SpringDao%20springDao)%20%7B%0A%09%09this.springDao%20%3D%20springDao%3B%0A%09%7D%0A%0A%20%20%20%20%20%20%20%20public%20void%20ok()%7B%0A%09%09springDao.ok()%3B%0A%09%7D%0A%7D" wmode="transparent"> 收藏代码

package com.bless.springdemo.action;
public class SpringAction {
//注入对象springDao
private SpringDao springDao;
//一定要写被注入对象的set方法
public void setSpringDao(SpringDao springDao) {
this.springDao = springDao;
}
public void ok(){
springDao.ok();
}
}

随后编写spring的xml文件，<bean>中的name属性是class属性的一个别名，class属性指类的全名，因为在SpringAction中有一个公共属性Springdao，所以要在<bean>标签中创建一个<property>标签指定SpringDao。<property>标签中的name就是SpringAction类中的SpringDao属性名，ref指下面<bean name="springDao"...>，这样其实是spring将SpringDaoImpl对象实例化并且调用SpringAction的 setSpringDao方法将SpringDao注入：

Java代码 <EMBED height=15 type=application/x-shockwave-flash pluginspage=http://www.macromedia.com/go/getflashplayer width=14 src=http://blessht.iteye.com/javascripts/syntaxhighlighter/clipboard_new.swf allowscriptaccess="always" quality="high" flashvars="clipboard=%3C!--%E9%85%8D%E7%BD%AEbean%2C%E9%85%8D%E7%BD%AE%E5%90%8E%E8%AF%A5%E7%B1%BB%E7%94%B1spring%E7%AE%A1%E7%90%86--%3E%0A%09%3Cbean%20name%3D%22springAction%22%20class%3D%22com.bless.springdemo.action.SpringAction%22%3E%0A%09%09%3C!--(1)%E4%BE%9D%E8%B5%96%E6%B3%A8%E5%85%A5%2C%E9%85%8D%E7%BD%AE%E5%BD%93%E5%89%8D%E7%B1%BB%E4%B8%AD%E7%9B%B8%E5%BA%94%E7%9A%84%E5%B1%9E%E6%80%A7--%3E%0A%09%09%3Cproperty%20name%3D%22springDao%22%20ref%3D%22springDao%22%3E%3C%2Fproperty%3E%0A%09%3C%2Fbean%3E%0A%3Cbean%20name%3D%22springDao%22%20class%3D%22com.bless.springdemo.dao.impl.SpringDaoImpl%22%3E%3C%2Fbean%3E" wmode="transparent"> 收藏代码

<bean name="springAction" class="com.bless.springdemo.action.SpringAction">
<property name="springDao" ref="springDao"></property>
</bean>
<bean name="springDao" class="com.bless.springdemo.dao.impl.SpringDaoImpl"></bean>

构造器注入

这种方式的注入是指带有参数的构造函数注入，看下面的例子，我创建了两个成员变量SpringDao和User，但是并未设置对象的set方法，所以就不能支持第一种注入方式，这里的注入方式是在SpringAction的构造函数中注入，也就是说在创建SpringAction对象时要将SpringDao和User两个参数值传进来：

Java代码 <EMBED height=15 type=application/x-shockwave-flash pluginspage=http://www.macromedia.com/go/getflashplayer width=14 src=http://blessht.iteye.com/javascripts/syntaxhighlighter/clipboard_new.swf allowscriptaccess="always" quality="high" flashvars="clipboard=public%20class%20SpringAction%20%7B%0A%09%2F%2F%E6%B3%A8%E5%85%A5%E5%AF%B9%E8%B1%A1springDao%0A%09private%20SpringDao%20springDao%3B%0A%09private%20User%20user%3B%0A%09%0A%09public%20SpringAction(SpringDao%20springDao%2CUser%20user)%7B%0A%09%09this.springDao%20%3D%20springDao%3B%0A%09%09this.user%20%3D%20user%3B%0A%09%09System.out.println(%22%E6%9E%84%E9%80%A0%E6%96%B9%E6%B3%95%E8%B0%83%E7%94%A8springDao%E5%92%8Cuser%22)%3B%0A%09%7D%0A%20%20%20%20%20%20%20%20%0A%20%20%20%20%20%20%20%20public%20void%20save()%7B%0A%09%09user.setName(%22%E5%8D%A1%E5%8D%A1%22)%3B%0A%09%09springDao.save(user)%3B%0A%09%7D%0A%7D" wmode="transparent"> 收藏代码

public class SpringAction {
//注入对象springDao
private SpringDao springDao;
private User user;
public SpringAction(SpringDao springDao,User user){
this.springDao = springDao;
this.user = user;
System.out.println("构造方法调用springDao和user");
}
public void save(){
user.setName("卡卡");
springDao.save(user);
}
}

在XML文件中同样不用<property>的形式，而是使用<constructor-arg>标签，ref属性同样指向其它<bean>标签的name属性：

Xml代码 <EMBED height=15 type=application/x-shockwave-flash pluginspage=http://www.macromedia.com/go/getflashplayer width=14 src=http://blessht.iteye.com/javascripts/syntaxhighlighter/clipboard_new.swf allowscriptaccess="always" quality="high" flashvars="clipboard=%3C!--%E9%85%8D%E7%BD%AEbean%2C%E9%85%8D%E7%BD%AE%E5%90%8E%E8%AF%A5%E7%B1%BB%E7%94%B1spring%E7%AE%A1%E7%90%86--%3E%0A%09%3Cbean%20name%3D%22springAction%22%20class%3D%22com.bless.springdemo.action.SpringAction%22%3E%0A%09%09%3C!--(2)%E5%88%9B%E5%BB%BA%E6%9E%84%E9%80%A0%E5%99%A8%E6%B3%A8%E5%85%A5%2C%E5%A6%82%E6%9E%9C%E4%B8%BB%E7%B1%BB%E6%9C%89%E5%B8%A6%E5%8F%82%E7%9A%84%E6%9E%84%E9%80%A0%E6%96%B9%E6%B3%95%E5%88%99%E9%9C%80%E6%B7%BB%E5%8A%A0%E6%AD%A4%E9%85%8D%E7%BD%AE--%3E%0A%09%09%3Cconstructor-arg%20ref%3D%22springDao%22%3E%3C%2Fconstructor-arg%3E%0A%09%09%3Cconstructor-arg%20ref%3D%22user%22%3E%3C%2Fconstructor-arg%3E%0A%09%3C%2Fbean%3E%0A%20%20%20%20%20%20%20%20%3Cbean%20name%3D%22springDao%22%20class%3D%22com.bless.springdemo.dao.impl.SpringDaoImpl%22%3E%3C%2Fbean%3E%0A%20%20%20%20%20%20%20%20%20%3Cbean%20name%3D%22user%22%20class%3D%22com.bless.springdemo.vo.User%22%3E%3C%2Fbean%3E" wmode="transparent"> 收藏代码

<bean name="springAction" class="com.bless.springdemo.action.SpringAction">
<constructor-arg ref="springDao"></constructor-arg>
<constructor-arg ref="user"></constructor-arg>
</bean>
<bean name="springDao" class="com.bless.springdemo.dao.impl.SpringDaoImpl"></bean>
<bean name="user" class="com.bless.springdemo.vo.User"></bean>

解决构造方法参数的不确定性，你可能会遇到构造方法传入的两参数都是同类型的，为了分清哪个该赋对应值，则需要进行一些小处理：

下面是设置index，就是参数位置：

<bean name="springAction" class="com.bless.springdemo.action.SpringAction">
<constructor-arg index="0" ref="springDao"></constructor-arg>
<constructor-arg index="1" ref="user"></constructor-arg>
</bean>

另一种是设置参数类型：

<constructor-arg type="java.lang.String" ref=""/>

静态工厂的方法注入

静态工厂顾名思义，就是通过调用静态工厂的方法来获取自己需要的对象，为了让spring管理所有对象，我们不能直接通过"工程类.静态方法()"来获取对象，而是依然通过spring注入的形式获取：

Java代码 <EMBED height=15 type=application/x-shockwave-flash pluginspage=http://www.macromedia.com/go/getflashplayer width=14 src=http://blessht.iteye.com/javascripts/syntaxhighlighter/clipboard_new.swf allowscriptaccess="always" quality="high" flashvars="clipboard=package%20com.bless.springdemo.factory%3B%0A%0Aimport%20com.bless.springdemo.dao.FactoryDao%3B%0Aimport%20com.bless.springdemo.dao.impl.FactoryDaoImpl%3B%0Aimport%20com.bless.springdemo.dao.impl.StaticFacotryDaoImpl%3B%0A%0Apublic%20class%20DaoFactory%20%7B%0A%09%2F%2F%E9%9D%99%E6%80%81%E5%B7%A5%E5%8E%82%0A%09public%20static%20final%20FactoryDao%20getStaticFactoryDaoImpl()%7B%0A%09%09return%20new%20StaticFacotryDaoImpl()%3B%0A%09%7D%0A%7D" wmode="transparent"> 收藏代码

package com.bless.springdemo.factory;
import com.bless.springdemo.dao.FactoryDao;
import com.bless.springdemo.dao.impl.FactoryDaoImpl;
import com.bless.springdemo.dao.impl.StaticFacotryDaoImpl;
public class DaoFactory {
//静态工厂
public static final FactoryDao getStaticFactoryDaoImpl(){
return new StaticFacotryDaoImpl();
}
}

同样看关键类，这里我需要注入一个FactoryDao对象，这里看起来跟第一种注入一模一样，但是看随后的xml会发现有很大差别:

Java代码 <EMBED height=15 type=application/x-shockwave-flash pluginspage=http://www.macromedia.com/go/getflashplayer width=14 src=http://blessht.iteye.com/javascripts/syntaxhighlighter/clipboard_new.swf allowscriptaccess="always" quality="high" flashvars="clipboard=%20public%20class%20SpringAction%20%7B%0A%20%20%20%20%20%20%20%20%2F%2F%E6%B3%A8%E5%85%A5%E5%AF%B9%E8%B1%A1%0A%09private%20FactoryDao%20staticFactoryDao%3B%0A%09%0A%09public%20void%20staticFactoryOk()%7B%0A%09%09staticFactoryDao.saveFactory()%3B%0A%09%7D%0A%09%2F%2F%E6%B3%A8%E5%85%A5%E5%AF%B9%E8%B1%A1%E7%9A%84set%E6%96%B9%E6%B3%95%0A%09public%20void%20setStaticFactoryDao(FactoryDao%20staticFactoryDao)%20%7B%0A%09%09this.staticFactoryDao%20%3D%20staticFactoryDao%3B%0A%09%7D%0A%7D" wmode="transparent"> 收藏代码

public class SpringAction {
//注入对象
private FactoryDao staticFactoryDao;
public void staticFactoryOk(){
staticFactoryDao.saveFactory();
}
//注入对象的set方法
public void setStaticFactoryDao(FactoryDao staticFactoryDao) {
this.staticFactoryDao = staticFactoryDao;
}
}

Spring的IOC配置文件，注意看<bean name="staticFactoryDao">指向的class并不是FactoryDao的实现类，而是指向静态工厂 DaoFactory，并且配置 factory-method="getStaticFactoryDaoImpl"指定调用哪个工厂方法：

Xml代码 <EMBED height=15 type=application/x-shockwave-flash pluginspage=http://www.macromedia.com/go/getflashplayer width=14 src=http://blessht.iteye.com/javascripts/syntaxhighlighter/clipboard_new.swf allowscriptaccess="always" quality="high" flashvars="clipboard=%3C!--%E9%85%8D%E7%BD%AEbean%2C%E9%85%8D%E7%BD%AE%E5%90%8E%E8%AF%A5%E7%B1%BB%E7%94%B1spring%E7%AE%A1%E7%90%86--%3E%0A%09%3Cbean%20name%3D%22springAction%22%20class%3D%22com.bless.springdemo.action.SpringAction%22%20%3E%0A%09%09%3C!--(3)%E4%BD%BF%E7%94%A8%E9%9D%99%E6%80%81%E5%B7%A5%E5%8E%82%E7%9A%84%E6%96%B9%E6%B3%95%E6%B3%A8%E5%85%A5%E5%AF%B9%E8%B1%A1%2C%E5%AF%B9%E5%BA%94%E4%B8%8B%E9%9D%A2%E7%9A%84%E9%85%8D%E7%BD%AE%E6%96%87%E4%BB%B6(3)--%3E%0A%09%09%3Cproperty%20name%3D%22staticFactoryDao%22%20ref%3D%22staticFactoryDao%22%3E%3C%2Fproperty%3E%0A%20%20%20%20%20%20%20%20%20%20%20%20%20%20%20%20%3C%2Fproperty%3E%0A%09%3C%2Fbean%3E%0A%09%3C!--(3)%E6%AD%A4%E5%A4%84%E8%8E%B7%E5%8F%96%E5%AF%B9%E8%B1%A1%E7%9A%84%E6%96%B9%E5%BC%8F%E6%98%AF%E4%BB%8E%E5%B7%A5%E5%8E%82%E7%B1%BB%E4%B8%AD%E8%8E%B7%E5%8F%96%E9%9D%99%E6%80%81%E6%96%B9%E6%B3%95--%3E%0A%09%3Cbean%20name%3D%22staticFactoryDao%22%20class%3D%22com.bless.springdemo.factory.DaoFactory%22%20factory-method%3D%22getStaticFactoryDaoImpl%22%3E%3C%2Fbean%3E%0A%09" wmode="transparent"> 收藏代码

<bean name="springAction" class="com.bless.springdemo.action.SpringAction" >
<property name="staticFactoryDao" ref="staticFactoryDao"></property>
</property>
</bean>
<bean name="staticFactoryDao" class="com.bless.springdemo.factory.DaoFactory" factory-method="getStaticFactoryDaoImpl"></bean>

实例工厂的方法注入

实例工厂的意思是获取对象实例的方法不是静态的，所以你需要首先new工厂类，再调用普通的实例方法：

public class DaoFactory {
//实例工厂
public FactoryDao getFactoryDaoImpl(){
return new FactoryDaoImpl();
}
}

那么下面这个类没什么说的，跟前面也很相似，但是我们需要通过实例工厂类创建FactoryDao对象：

Java代码 <EMBED height=15 type=application/x-shockwave-flash pluginspage=http://www.macromedia.com/go/getflashplayer width=14 src=http://blessht.iteye.com/javascripts/syntaxhighlighter/clipboard_new.swf allowscriptaccess="always" quality="high" flashvars="clipboard=public%20class%20SpringAction%20%7B%0A%09%2F%2F%E6%B3%A8%E5%85%A5%E5%AF%B9%E8%B1%A1%0A%09private%20FactoryDao%20factoryDao%3B%0A%09%0A%09public%20void%20factoryOk()%7B%0A%09%09factoryDao.saveFactory()%3B%0A%09%7D%0A%0A%09public%20void%20setFactoryDao(FactoryDao%20factoryDao)%20%7B%0A%09%09this.factoryDao%20%3D%20factoryDao%3B%0A%09%7D%0A%7D" wmode="transparent"> 收藏代码

public class SpringAction {
//注入对象
private FactoryDao factoryDao;
public void factoryOk(){
factoryDao.saveFactory();
}
public void setFactoryDao(FactoryDao factoryDao) {
this.factoryDao = factoryDao;
}
}

最后看spring配置文件：

Xml代码 <EMBED height=15 type=application/x-shockwave-flash pluginspage=http://www.macromedia.com/go/getflashplayer width=14 src=http://blessht.iteye.com/javascripts/syntaxhighlighter/clipboard_new.swf allowscriptaccess="always" quality="high" flashvars="clipboard=%3C!--%E9%85%8D%E7%BD%AEbean%2C%E9%85%8D%E7%BD%AE%E5%90%8E%E8%AF%A5%E7%B1%BB%E7%94%B1spring%E7%AE%A1%E7%90%86--%3E%0A%09%3Cbean%20name%3D%22springAction%22%20class%3D%22com.bless.springdemo.action.SpringAction%22%3E%0A%09%09%3C!--(4)%E4%BD%BF%E7%94%A8%E5%AE%9E%E4%BE%8B%E5%B7%A5%E5%8E%82%E7%9A%84%E6%96%B9%E6%B3%95%E6%B3%A8%E5%85%A5%E5%AF%B9%E8%B1%A1%2C%E5%AF%B9%E5%BA%94%E4%B8%8B%E9%9D%A2%E7%9A%84%E9%85%8D%E7%BD%AE%E6%96%87%E4%BB%B6(4)--%3E%0A%09%09%3Cproperty%20name%3D%22factoryDao%22%20ref%3D%22factoryDao%22%3E%3C%2Fproperty%3E%0A%09%3C%2Fbean%3E%0A%09%0A%09%3C!--(4)%E6%AD%A4%E5%A4%84%E8%8E%B7%E5%8F%96%E5%AF%B9%E8%B1%A1%E7%9A%84%E6%96%B9%E5%BC%8F%E6%98%AF%E4%BB%8E%E5%B7%A5%E5%8E%82%E7%B1%BB%E4%B8%AD%E8%8E%B7%E5%8F%96%E5%AE%9E%E4%BE%8B%E6%96%B9%E6%B3%95--%3E%0A%09%3Cbean%20name%3D%22daoFactory%22%20class%3D%22com.bless.springdemo.factory.DaoFactory%22%3E%3C%2Fbean%3E%0A%09%3Cbean%20name%3D%22factoryDao%22%20factory-bean%3D%22daoFactory%22%20factory-method%3D%22getFactoryDaoImpl%22%3E%3C%2Fbean%3E" wmode="transparent"> 收藏代码

<bean name="springAction" class="com.bless.springdemo.action.SpringAction">
<property name="factoryDao" ref="factoryDao"></property>
</bean>
<bean name="daoFactory" class="com.bless.springdemo.factory.DaoFactory"></bean>
<bean name="factoryDao" factory-bean="daoFactory" factory-method="getFactoryDaoImpl"></bean>