【Spring】Spring的注入

【对象的注入】

 IOC容器的对象实例化是通过配置文件来实现的。术语上这叫做注入。注入有两种形式，采用构造方法注入和采用setter注入。具体的注入形式如下

**************构造方法方式*******************

UserManagerImpl类：

package com.bjpowernode.spring.manager; import com.bjpowernode.spring.dao.UserDao; public class UserManagerImpl implements UserManager { private UserDao userDao; public UserManagerImpl(UserDao userDao) { this.userDao = userDao; } }

配置文件代码：

<?xml version="1.0" encoding="UTF-8"?> <beans xmlns="http://www.springframework.org/schema/beans" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns:aop="http://www.springframework.org/schema/aop" xmlns:tx="http://www.springframework.org/schema/tx" xsi:schemaLocation="http://www.springframework.org/schema/beans http://www.springframework.org/schema/beans/spring-beans-2.0.xsd http://www.springframework.org/schema/aop http://www.springframework.org/schema/aop/spring-aop-2.0.xsd http://www.springframework.org/schema/tx http://www.springframework.org/schema/tx/spring-tx-2.0.xsd"> <bean id="userDao4Mysql" class="com.bjpowernode.spring.dao.UserDao4MySqlImpl" /> <bean id="userManager" class="com.bjpowernode.spring.manager.UserManagerImpl"> <constructor-arg ref="userDao4Mysql" /> </bean> </beans>

****************setter方式*****************

UserManagerImpl类：

package com.bjpowernode.spring.manager; import com.bjpowernode.spring.dao.UserDao; public class UserManagerImpl implements UserManager { private UserDao userDao; public void setUserDao(UserDao userDao) { this.userDao = userDao; } }

配置文件代码：

<?xml version="1.0" encoding="UTF-8"?> <beans xmlns="http://www.springframework.org/schema/beans" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns:aop="http://www.springframework.org/schema/aop" xmlns:tx="http://www.springframework.org/schema/tx" xsi:schemaLocation="http://www.springframework.org/schema/beans http://www.springframework.org/schema/beans/spring-beans-2.0.xsd http://www.springframework.org/schema/aop http://www.springframework.org/schema/aop/spring-aop-2.0.xsd http://www.springframework.org/schema/tx http://www.springframework.org/schema/tx/spring-tx-2.0.xsd"> <bean id="userDao4Mysql" class="com.bjpowernode.spring.dao.UserDao4MySqlImpl" /> <bean id="userManager" class="com.bjpowernode.spring.manager.UserManagerImpl"> <!-- <constructor-arg ref="userDao4Mysql" /> --> <property name="userDao" ref="userDao4Mysql" /> </bean> </beans>

比较：

1.构造方法：

对于依赖关系无须变化的Bean，构造注入更有用处；因为没有setter方法，所有的依赖关系全部在构造器内设定，因此，不用担心后续代码对依赖关系的破坏。依赖关系只能在构造器中设定，则只有组件的创建者才能改变组件的依赖关系。对组件的调用者而言，组件内部的依赖关系完全透明，更符合高内聚的原则。

构造注入可以在构造器中决定依赖关系的注入顺序。

2，setter方法：

与传统的JavaBean的写法更相似，程序员更容易理解、接受，通过setter方式设定依赖关系显得更加直观、明显；对于复杂的依赖关系，如果采用构造注入，会导致构造器过于臃肿，难以阅读。Spring在创建Bean实例时，需要同时实例化其依赖的全部实例，因而导致死你功能下降。而使用设置注入，则避免这下问题；尤其在某些属性可选的情况下，多参数的构造器更加笨拙。

【属性编辑器】

Spring内置了一些属性编辑器，可以将一些普通常用的属性注入，将Spring配置文件中的String类型转换成相应的Java对象。例如一个类里面的一个整型属性，在配置文件中我们是通过String类型的数字直接进行配置即可。如下示例：

Bean1类：

package com.bjpowernode.spring; import java.util.Date; import java.util.List; import java.util.Map; import java.util.Set; public class Bean1 { private String strValue; private int intValue; private List listValue; private Set setValue; private String[] arrayValue; private Map mapValue; private Date dateValue; //get和set略 }

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" xmlns:aop="http://www.springframework.org/schema/aop" xmlns:tx="http://www.springframework.org/schema/tx" xsi:schemaLocation="http://www.springframework.org/schema/beans http://www.springframework.org/schema/beans/spring-beans-2.0.xsd http://www.springframework.org/schema/aop http://www.springframework.org/schema/aop/spring-aop-2.0.xsd http://www.springframework.org/schema/tx http://www.springframework.org/schema/tx/spring-tx-2.0.xsd" default-lazy-init="true"> <bean id="bean1" class="com.bjpowernode.spring.Bean1"> <property name="strValue" value="Hello_Spring" /> <!-- <property name="intValue" value="123"/> --> <property name="intValue"> <value>123</value> </property> <property name="listValue"> <list> <value>list1</value> <value>list2</value> </list> </property> <property name="setValue"> <set> <value>set1</value> <value>set2</value> </set> </property> <property name="arrayValue"> <list> <value>array1</value> <value>array2</value> </list> </property> <property name="mapValue"> <map> <entry key="k1" value="v1" /> <entry key="k2" value="v2" /> </map> </property> </bean> </beans>

测试方法：

package test; import org.springframework.beans.factory.BeanFactory; import org.springframework.context.support.ClassPathXmlApplicationContext; import com.bjpowernode.spring.Bean1; import junit.framework.TestCase; public class InjectionTest extends TestCase { private BeanFactory factory; @Override protected void setUp() throws Exception { String[] configLocations = new String[] { "applicationContext-beans.xml"}; factory = new ClassPathXmlApplicationContext(configLocations); } @Override protected void tearDown() throws Exception { } public void testInjection1() { Bean1 bean1 = (Bean1) factory.getBean("bean1"); System.out.println("bean1.strValue=" + bean1.getStrValue()); System.out.println("bean1.intValue=" + bean1.getIntValue()); System.out.println("bean1.listValue=" + bean1.getListValue()); System.out.println("bean1.setValue=" + bean1.getSetValue()); System.out.println("bean1.arrayValue=" + bean1.getArrayValue()); System.out.println("bean1.mapValue=" + bean1.getMapValue()); System.out.println("bean1.dateValue=" + bean1.getDateValue()); } }

【自定义属性编辑器】

Spring具有多个自定义编辑器，它们能够自动把注入的String值转化为更复杂的类型。例如Date类型，如果直接按照上面实例的方式进行配置，就会报错如下：

org.springframework.beans.factory.BeanCreationException:Error creating bean with name 'bean' defined in class path resource[applicationContext.xml]: Initialization of bean failed; nested exception isorg.springframework.beans.TypeMismatchException: Failed to convert propertyvalue of type [java.lang.String] to required type [java.util.Date] for property'date';

因为Spring没有内置Date的属性编辑器，需要我们自己创建。创建过程：

1.编写UtilDatePropertyEditor类，继承PropertyEditorSupport，覆盖setAsText()方法，其中text参数就是配置文件中的值。我们的任务就是把text转换成date类型的值。

package com.bjpowernode.spring; import java.beans.PropertyEditorSupport; import java.text.ParseException; import java.text.SimpleDateFormat; import java.util.Date; /** * java.util.Date属性编辑器 * @author Administrator * */ public class UtilDatePropertyEditor extends PropertyEditorSupport { private String pattern; @Override public void setAsText(String text) throws IllegalArgumentException { System.out.println("---UtilDatePropertyEditor.setAsText()--->" + text); try { Date date = new SimpleDateFormat(pattern).parse(text); this.setValue(date); } catch (ParseException e) { // TODO Auto-generated catch block e.printStackTrace(); throw new IllegalArgumentException(text); } } public void setPattern(String pattern) { this.pattern = pattern; } }

2.将自定义的属性编辑器注入到spring中，为了方便管理我们再新建一个配置文件applicationContext-editor.xml（测试时记得将该配置文件一同加载即可）

<?xml version="1.0" encoding="UTF-8"?> <beans xmlns="http://www.springframework.org/schema/beans" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns:aop="http://www.springframework.org/schema/aop" xmlns:tx="http://www.springframework.org/schema/tx" xsi:schemaLocation="http://www.springframework.org/schema/beans http://www.springframework.org/schema/beans/spring-beans-2.0.xsd http://www.springframework.org/schema/aop http://www.springframework.org/schema/aop/spring-aop-2.0.xsd http://www.springframework.org/schema/tx http://www.springframework.org/schema/tx/spring-tx-2.0.xsd"> <bean id="customEditors" class="org.springframework.beans.factory.config.CustomEditorConfigurer"> <property name="customEditors"> <map> <entry key="java.util.Date"> <bean class="com.bjpowernode.spring.UtilDatePropertyEditor"> <property name="pattern" value="yyyy年MM月dd日"/> </bean> </entry> </map> </property> </bean> </beans>