第四章 构造器注入,自动装配,集合注入

控制反转(IOC):说简单点就是实例化对象的控制权发生了转变,以前是我们自己new,现在交给Spring这个大工厂去实例化,如果我们现在要用对象,就直接向Spring这个大工厂索取就可以了.就像以前是自己做饭吃,现在是在餐馆点菜吃,只不过是点菜的方式有两种,一个set方式,一种构造器方式.

 构造器方式注入
构造器参数类型匹配
要求构造参数非常明确,即参数列表不会有同类型的参数
以水果Service层为示例:
Service层需要持有Dao层对象,才能调用Dao层的方法.
服务层接口:
public interface FruitService {
public void create();
}
服务层实现类:
public class FruitServiceImpl implements FruitService {
private FruitDao fruitDao;

public FruitServiceImpl(FruitDao fruitDao) {
super();
this.fruitDao = fruitDao;
}

@Override
public void create() {
fruitDao.create();
}
}
可以看到,和前面的set注入不同,提供的是我们熟悉的构造方法
配置文件:
<?xml version="1.0" encoding="UTF-8"?>
<beans xmlns="http://www.springframework.org/schema/beans"
xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xsi:schemaLocation="http://www.springframework.org/schema/beans
http://www.springframework.org/schema/beans/spring-beans-2.5.xsd">
<bean id="fruitDao" class="dao.impl.FruitDaoImpl" />
<bean id="fruitService" class="service.impl.FruitServiceImpl">
<constructor-arg type="dao.FruitDao" ref="fruitDao"/>
</bean>
</beans>
Test:
public class Test {

public static void main(String[] args) {
ApplicationContext acx = new ClassPathXmlApplicationContext(
"chapter2.xml");
FruitService fruitService = (FruitService) acx
.getBean("fruitService");
fruitService.create();
}
}


构造参数索引
可以解决参数同类型问题,并且配置时不用去维护参数顺序的问题,如果使用构造器注入(推荐使用这种方式),或者将前两者结合起来一起使用.
给服务层添加了两个字符串属性name, address, 注意这里只是为了演示方便
public class FruitServiceImpl implements FruitService {
private FruitDao fruitDao;
private String name;
private String address;

public FruitServiceImpl(FruitDao fruitDao) {
super();
this.fruitDao = fruitDao;
}

public FruitServiceImpl(FruitDao fruitDao, String name, String address) {
super();
this.fruitDao = fruitDao;
this.name = name;
this.address = address;
}

@Override
public void create() {
fruitDao.create();
}

public FruitDao getFruitDao() {
return fruitDao;
}

public void setFruitDao(FruitDao fruitDao) {
this.fruitDao = fruitDao;
}

public String getName() {
return name;
}

public void setName(String name) {
this.name = name;
}

public String getAddress() {
return address;
}

public void setAddress(String address) {
this.address = address;
}
}
配置:
第一种方式:
<?xml version="1.0" encoding="UTF-8"?>
<beans xmlns="http://www.springframework.org/schema/beans"
xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xsi:schemaLocation="http://www.springframework.org/schema/beans
http://www.springframework.org/schema/beans/spring-beans-2.5.xsd">
<bean id="fruitDao" class="dao.impl.FruitDaoImpl" />
<bean id="fruitService" class="service.impl.FruitServiceImpl">
<constructor-arg index="0" ref="fruitDao" />
<constructor-arg index="1" value="wdpc" />
<constructor-arg index="2" value="武大" />
</bean>
</beans>
第二种方式:
<?xml version="1.0" encoding="UTF-8"?>
<beans xmlns="http://www.springframework.org/schema/beans"
xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xsi:schemaLocation="http://www.springframework.org/schema/beans
http://www.springframework.org/schema/beans/spring-beans-2.5.xsd">
<bean id="fruitDao" class="dao.impl.FruitDaoImpl" />
<bean id="fruitService" class="service.impl.FruitServiceImpl">
<constructor-arg index="0" type="dao.FruitDao" ref="fruitDao" />
<constructor-arg index="1" type="java.lang.String" value="wdpc" />
<constructor-arg index="2" type="java.lang.String" value="武大" />
</bean>
</beans>
Test：
public class Test {

public static void main(String[] args) {
ApplicationContext acx = new ClassPathXmlApplicationContext(
"chapter2.xml");
FruitService fruitService = (FruitService) acx
.getBean("fruitService");
fruitService.create();
System.out.println(((FruitServiceImpl)fruitService).getName());
System.out.println(((FruitServiceImpl)fruitService).getAddress());
}
}
(FruitServiceImpl)fruitService)注意这一句,因为fruitService是服务层的接口,接口中只暴露了一个create方法,所以我们只能调用create方法,如果想调用其它的get方法,就需要将接口强转为实现类,注意这一点,这也是使用接口的一个好处,只暴露接口中定义的方法,

 集合的注入
1. set
2. list
3. properties
4. map
import java.util.ArrayList;
import java.util.HashMap;
import java.util.HashSet;
import java.util.List;
import java.util.Map;
import java.util.Properties;
import java.util.Set;

public class CollectionService {
private Set<String> sets = new HashSet<String>();
private List<String> lists = new ArrayList<String>();
private Properties properties = new Properties();
private Map<String, String> mpas = new HashMap<String, String>();

public Set<String> getSets() {
return sets;
}

public void setSets(Set<String> sets) {
this.sets = sets;
}

public List<String> getLists() {
return lists;
}

public void setLists(List<String> lists) {
this.lists = lists;
}

public Properties getProperties() {
return properties;
}

public void setProperties(Properties properties) {
this.properties = properties;
}

public Map<String, String> getMpas() {
return mpas;
}

public void setMpas(Map<String, String> mpas) {
this.mpas = mpas;
}
}

配置:
<?xml version="1.0" encoding="UTF-8"?>
<beans xmlns="http://www.springframework.org/schema/beans"
xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xsi:schemaLocation="http://www.springframework.org/schema/beans
http://www.springframework.org/schema/beans/spring-beans-2.5.xsd">
<bean id="collectionService" class="service.impl.CollectionService">
<property name="sets">
<set>
<value>set1</value>
<value>set2</value>
<value>set3</value>
</set>
</property>
<property name="lists">
<list>
<value>list1</value>
<value>list2</value>
<value>list3</value>
</list>
</property>
<property name="properties">
<props>
<prop key="pkey1">pkey1</prop>
<prop key="pkey2">pkey2</prop>
<prop key="pkey3">pkey3</prop>
</props>
</property>
<property name="mpas">
<map>
<entry key="mkey1" value="mkey1" />
<entry key="mkey2" value="mkey2" />
<entry key="mkey3" value="mkey3" />
</map>
</property>
</bean>
</beans>
Test:
public class Test {

public static void main(String[] args) {
ApplicationContext acx = new ClassPathXmlApplicationContext(
"chapter2.xml");
CollectionService collectionService = (CollectionService) acx
.getBean("collectionService");
Set<String> set = collectionService.getSets();
for (String s : set) {
System.out.println(s);
}
System.out.println("========================");
List<String> lists = collectionService.getLists();
for (String s : lists) {
System.out.println(s);
}
System.out.println("========================");
Properties properties = collectionService.getProperties();
for (Object key : properties.keySet()) {
System.out
.println(key + ":" + properties.getProperty((String) key));
}
System.out.println("========================");
Map<String, String> mpas = collectionService.getMpas();
for(String key : mpas.keySet()){
System.out
.println(key + ":" + mpas.get((String) key));
}
}
}

 自动装配
byName
<?xml version="1.0" encoding="UTF-8"?>
<beans xmlns="http://www.springframework.org/schema/beans"
xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xsi:schemaLocation="http://www.springframework.org/schema/beans
http://www.springframework.org/schema/beans/spring-beans-2.5.xsd">
<bean id="fruitDao" class="dao.impl.FruitDaoImpl" />
<bean id="fruitService" class="service.impl.FruitServiceImpl"
autowire="byName" />
</beans>
需要注意的地方: <bean id="fruitDao" class="dao.impl.FruitDaoImpl" />
id="fruitDao"一定要和服务层的属性名称对应,即FruitDaoImpl类里面一定要有一个名称为fruitDao的属性.

byType
<?xml version="1.0" encoding="UTF-8"?>
<beans xmlns="http://www.springframework.org/schema/beans"
xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xsi:schemaLocation="http://www.springframework.org/schema/beans
http://www.springframework.org/schema/beans/spring-beans-2.5.xsd">
<bean id="fruitDao" class="dao.impl.FruitDaoImpl" />
<bean id="fruitService" class="service.impl.FruitServiceImpl"
autowire="byType" />
</beans>
需要保证FruitServiceImpl类中有一个属性类型是FruitDao类型即可.

尽量不要用自动装配的特性,因为会产生二异性,特别是按类型装配,