这里将模仿Spring实现一种基于xml配置文件的依赖注入机制。文件中将实现3中注入，一是单值注入，包括int,float，double，char等，也包括String注入；二是Java容器注入，包括List，Set，Map三种容器的注入，最后一种是java
bean对象注入。
实现的机制是，使用Dom4j对xml配置文件进行解析，这里使用dom4j的Element
Handler机制，一种类似与责任链模式的实现机制；对于java对象的构建使用反射机制，这里主要是针对得到的类的Field进行set赋值。我试图通过调用Method的invoke方法调用类本身的setter方法，但是由于通过xml解析得到的值都是String，如果将这些String动态的转换为相应的确定类型是个难点，Method的invoke方法，如果形参是int，而传入java.lang.Integer，它不会认，所以尝试失败，只能通过Field的set方法传入特定值。
配置文件setting.xml
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<?xml version="1.0"
encoding="UTF-8"?>
<beans>
<bean id="me"
class="com.zj.ioc.di.imp.Person">
<property name="name">
<value>ZJ</value>
</property>
<property name="age">
<value>26</value>
</property>
<property name="height">
<value>1.78</value>
</property>
</bean>
<bean id="you"
class="com.zj.ioc.di.imp.Person">
<property name="name">
<value>Mary</value>
</property>
<property name="age">
<value>27</value>
</property>
<property name="height">
<value>1.66</value>
</property>
</bean>
<bean id="myList"
class="com.zj.ioc.di.imp.ListOne">
<property name="msg">
<list>
<value>java</value>
<value>c</value>
<value>windows</value>
</list>
</property>
</bean>
<bean id="mySet"
class="com.zj.ioc.di.imp.SetOne">
<property name="msg">
<set>
<value>tom</value>
<value>cat</value>
<value>dog</value>
</set>
</property>
</bean>
<bean id="myMap"
class="com.zj.ioc.di.imp.MapOne">
<property name="msg">
<map>
<entry key="c">
<value>
</entry>
<entry key="j">
<value>
</entry>
<entry key="k">
<value>
</entry>
</map>
</property>
</bean>
<bean id="us"
class="com.zj.ioc.di.imp.Persons">
<property name="i">
<ref bean="me" />
</property>
<property name="u">
<ref bean="you" />
</property>
</bean>
</beans>
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依据setting.xml，这里将构建两个Person类的实例me和you：
Person.java
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package com.zj.ioc.di.imp;
public class Person {
private String name;
private int age;
private float height;
public String getName() {return name;}
public void setName(String name) {this.name = name;}
public int getAge() {return age;}
public void setAge(int age) {this.age = age;}
public float getHeight() {return height;}
public void setHeight(float height) {this.height = height;}
}
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紧接着，构建一个ListOne的实例myList：
ListOne.java
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package com.zj.ioc.di.imp;
import java.util.List;
public class ListOne {
private List<String> msg;
public List<String> getMsg()
{return msg;}
public void setMsg(List<String>
msg) {this.msg = msg;}
}
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紧接着，构建一个SetOne的实例mySet：
SetOne.java
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package com.zj.ioc.di.imp;
import java.util.Set;
public class SetOne {
private Set<String> msg;
public Set<String> getMsg() {return msg;}
public void setMsg(Set<String>
msg) {this.msg = msg;}
}
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紧接着，构建一个MapOne的实例myMap：
MapOne.java
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package com.zj.ioc.di.imp;
import java.util.Map;
public class MapOne {
private Map<String,String> msg;
public Map<String, String>
getMsg() {return msg;}
public void setMsg(Map<String,
String> msg) {this.msg = msg;}
}
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最后构建一个Persons类的实例us，其中包含me和you两个已经构建好的对象：
Persons.java
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package com.zj.ioc.di.imp;
public class Persons {
private Person i;
private Person u;
public Person getI() {return i;}
public void setI(Person i) {this.i = i;}
public Person getU() {return u;}
public void setU(Person u) {this.u = u;}
}
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主要的实现机制是(代码BeanFactory.java以及工程见附件)，
1.通过一个HashMap保存构造好的对象，key就是bean的id属性，value就是这个对象；
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private Map<String, Object> beanMap = new HashMap<String, Object>();
……
public Object getBean(String beanId) {
Object obj = beanMap.get(beanId);
return obj;
}
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查询时
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BeanFactory factory
= new BeanFactory();
factory.init("setting.xml");
Person p1 = (Person) factory.getBean("me");
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2.init方法读入配置文件setting.xml，并直接定位到beans下的bean元素，并实例化一个ElementHandler对其处理。
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public void init(String xmlUri) throws Exception {
SAXReader saxReader = new SAXReader();
File file = new File(xmlUri);
try {
saxReader.addHandler("/beans/bean", new BeanHandler());
saxReader.read(file);
} catch (DocumentException e) {
System.out.println(e.getMessage());
}
}
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3.ElementHandler，dom4j的ElementHandler接口有两个方法，一个是onStart()，它主要用于处理该元素的属性以及动态增加新的Handler类；另一个是onEnd()，它主要用于获得该元素的Text文本以及删除已添加的Handler。
BeanHandler
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private class BeanHandler implements ElementHandler {
Object obj = null;
public void .Start(ElementPath path) {
Element beanElement =
path.getCurrent();
Attribute classAttribute =
beanElement.attribute("class");
Class<?> bean = null;
try {
bean = Class.forName(classAttribute.getText());
} catch (ClassNotFoundException e) {
e.printStackTrace();
}
Field fields[] =
bean.getDeclaredFields();
Map<String, Field> mapField = new
HashMap<String, Field>();
for (Field field : fields)
mapField.put(field.getName(),
field);
try {
obj = bean.newInstance();
} catch (InstantiationException e) {
e.printStackTrace();
} catch (IllegalAccessException e) {
e.printStackTrace();
}
path.addHandler("property", new PropertyHandler(mapField, obj));
}
public void .End(ElementPath path) {
Element beanElement =
path.getCurrent();
Attribute idAttribute =
beanElement.attribute("id");
beanMap.put(idAttribute.getText(), obj);
path.removeHandler("property");
}
}
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PropertyHandler
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private class PropertyHandler implements ElementHandler {
Map<String, Field> mapField;
Object obj;
public
PropertyHandler(Map<String, Field> mapField, Object obj) {
this.mapField = mapField;
this.obj = obj;
}
public void .Start(ElementPath path) {
Element propertyElement =
path.getCurrent();
Attribute nameAttribute =
propertyElement.attribute("name");
path.addHandler("value", new ValueHandler(mapField, obj,
nameAttribute));
path.addHandler("list", new ListHandler(mapField, obj,
nameAttribute));
path.addHandler("set", new SetHandler(mapField, obj,
nameAttribute));
path.addHandler("map", new MapHandler(mapField, obj,
nameAttribute));
path.addHandler("ref", new RefHandler(mapField, obj,
nameAttribute));
}
public void .End(ElementPath path) {
path.removeHandler("value");
path.removeHandler("list");
path.removeHandler("set");
path.removeHandler("map");
path.removeHandler("ref");
}
}
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根据setting.xml，我们可以得到各种注入元素的Handler类处理流程图。
4.
setFieldValue()基于反射机制和相应的类信息得到Field的类型，并根据setting.xml设置它的值。
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private void setFieldValue(Object obj, Field field, String value) {
String fieldType =
field.getType().getSimpleName();
try {
if (fieldType.equals("int"))
field.setInt(obj, new Integer(value));
else if (fieldType.equals("float"))
field.setFloat(obj, new Float(value));
else if (fieldType.equals("boolean"))
field.setBoolean(obj, new Boolean(value));
else if (fieldType.equals("char"))
field.setChar(obj,
value.charAt(0));
else if (fieldType.equals("double"))
field.setDouble(obj, new Double(value));
else if (fieldType.equals("long"))
field.setLong(obj, new Long(value));
else
field.set(obj, value);
} catch (IllegalArgumentException e)
{
e.printStackTrace();
} catch (IllegalAccessException e) {
e.printStackTrace();
}
}
private void setFieldValue(Object obj, Field field,
List<String> value) {
try {
field.set(obj, value);
} catch (IllegalArgumentException e)
{
e.printStackTrace();
} catch (IllegalAccessException e) {
e.printStackTrace();
}
}
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5.测试
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public static void main(String[] args) {
try {
BeanFactory factory = new BeanFactory();
factory.init("setting.xml");
Person p1 = (Person) factory.getBean("me");
System.out.print(p1.getName() + " ");
System.out.print(p1.getAge() + " ");
System.out.println(p1.getHeight());
Person p2 = (Person) factory.getBean("you");
System.out.print(p2.getName() + " ");
System.out.print(p2.getAge() + " ");
System.out.println(p2.getHeight());
ListOne list = (ListOne)
factory.getBean("myList");
System.out.println(list.getMsg());
SetOne set = (SetOne) factory.getBean("mySet");
System.out.println(set.getMsg());
MapOne map = (MapOne) factory.getBean("myMap");
System.out.println(map.getMsg());
Persons us = (Persons) factory.getBean("us");
System.out.println(us.getI());
System.out.println(us.getU());
} catch (Exception e) {
e.printStackTrace();
}
}
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测试结果：
ZJ 26 1.78
Mary 27 1.66
[java, c, windows]
[cat, tom, dog]
{c=CHINA ,
j=JAPAN , k=KOREA
com.zj.ioc.di.imp.Person@1a 5ab41
com.zj.ioc.di.imp.Person@18e3e60
