简易的IOC实现

我把这个放在设计模式这一栏,是因为我们可以使用这种简单的相当于spring的IOC原理的一种设计方式,对产生任何bean 带来了方便了.对我自己的理解,它更像是一种dao工厂的实现.而在前面,我贴了一篇文章,名字叫:很好用的工厂模式的实现方式,和这个是差不多的,只不过那种是读取properties文件,而这种是在使用了一个工具:commons-digester.jar,它是一个专门用于读取xml文件的一个工具,我们可以在xml文件中,配置好我们的bean,然后使用一个digesterFactory,来对bean进行生产.
一、先设计一个xml文件
config.xml

<?xml version="1.0" encoding="UTF-8"?>

<beans>
  <bean id="user" type="com.hejianjiao.entity.User"></bean>
  <bean id="message" type="com.hejianjiao.entity.Message"></bean>
</beans>

<?xml version="1.0" encoding="UTF-8"?>

<beans>
  <bean id="user" type="com.hejianjiao.entity.User"></bean>
  <bean id="message" type="com.hejianjiao.entity.Message"></bean>
</beans>

这里的标签，我们可以自己定义。只不过现在没有使用DTD来对xml文件进行验证。然后我们就要设计两个对象了：Beans \ Bean

Beans.java
package com.hejianjiao.digester;

import java.util.HashMap;
import java.util.Iterator;

public class Beans {

    private HashMap<String, Bean> beans = new HashMap<String, Bean>();

    public Iterator<String> getBeans() {
        return beans.keySet().iterator();
    }

    public Bean getBean(String id) {
        return (Bean) beans.get(id);
    }

    public void addBean(Bean bean) {
        beans.put(String.valueOf(bean.getId()), bean);
    }

}

Bean.java

package com.hejianjiao.digester;

public class Bean {

    private String id;
    private String type;

    public String getId() {
        return id;
    }

    public void setId(String id) {
        this.id = id;
    }

    public String getType() {
        return type;
    }

    public void setType(String type) {
        this.type = type;
    }

}

Beans.java
package com.hejianjiao.digester;

import java.util.HashMap;
import java.util.Iterator;

public class Beans {

	private HashMap<String, Bean> beans = new HashMap<String, Bean>();

	public Iterator<String> getBeans() {
		return beans.keySet().iterator();
	}

	public Bean getBean(String id) {
		return (Bean) beans.get(id);
	}

	public void addBean(Bean bean) {
		beans.put(String.valueOf(bean.getId()), bean);
	}

}

Bean.java

package com.hejianjiao.digester;

public class Bean {

	private String id;
	private String type;

	public String getId() {
		return id;
	}

	public void setId(String id) {
		this.id = id;
	}

	public String getType() {
		return type;
	}

	public void setType(String type) {
		this.type = type;
	}

}

这个就是对xml文件的属性进行一个对象的标明。

三、就是一个DigesterFactory产生bean的工厂：

package com.hejianjiao.digester;

import java.io.File;
import java.io.IOException;

import org.apache.commons.digester.Digester;
import org.xml.sax.SAXException;

public class DigesterFactory {

    private static File input = new File(
            "src/com/hejianjiao/digester/config.xml");
    private static Digester digester = new Digester();
    private static DigesterFactory factory = null;

    private static Beans doDigester() {
        // 设置对XML文档资料是否进行DTD验证
        digester.setValidating(false);
        // 当遇到beans时,就产生一个Beans对象
        digester.addObjectCreate("beans", Beans.class);
        digester.addSetProperties("beans");
        // 当遇到 beans下边的bean时,就生产一个Bean对象
        digester.addObjectCreate("beans/bean", Bean.class);
        digester.addSetProperties("beans/bean");
        // 当再一次遇到bean对象时,就调用Beans中的addBean()方法
        digester.addSetNext("beans/bean", "addBean",
                "com.hejianjiao.digester.Bean");

        Beans beans = null;
        try {
            beans = (Beans) digester.parse(input);
        } catch (IOException e) {
            e.printStackTrace();
        } catch (SAXException e) {
            e.printStackTrace();
        }

        return beans;
    }

    @SuppressWarnings("static-access")
    public static Object getObject(String id) {
        Object obj = null;
        // 保证工厂的单一性
        if (factory == null) {
            factory = new DigesterFactory();
        }
        Bean bean = factory.doDigester().getBean(id);
        if (bean != null) {
            String className = bean.getType();
            try {
                obj = Class.forName(className).newInstance();
            } catch (InstantiationException e) {
                e.printStackTrace();
            } catch (IllegalAccessException e) {
                e.printStackTrace();
            } catch (ClassNotFoundException e) {
                System.out.println("Not found class named : " + className);
                e.printStackTrace();
            }
        }

        return obj;
    }

}

package com.hejianjiao.digester;

import java.io.File;
import java.io.IOException;

import org.apache.commons.digester.Digester;
import org.xml.sax.SAXException;

public class DigesterFactory {

	private static File input = new File(
			"src/com/hejianjiao/digester/config.xml");
	private static Digester digester = new Digester();
	private static DigesterFactory factory = null;

	private static Beans doDigester() {
		// 设置对XML文档资料是否进行DTD验证
		digester.setValidating(false);
		// 当遇到beans时,就产生一个Beans对象
		digester.addObjectCreate("beans", Beans.class);
		digester.addSetProperties("beans");
		// 当遇到 beans下边的bean时,就生产一个Bean对象
		digester.addObjectCreate("beans/bean", Bean.class);
		digester.addSetProperties("beans/bean");
		// 当再一次遇到bean对象时,就调用Beans中的addBean()方法
		digester.addSetNext("beans/bean", "addBean",
				"com.hejianjiao.digester.Bean");

		Beans beans = null;
		try {
			beans = (Beans) digester.parse(input);
		} catch (IOException e) {
			e.printStackTrace();
		} catch (SAXException e) {
			e.printStackTrace();
		}

		return beans;
	}

	@SuppressWarnings("static-access")
	public static Object getObject(String id) {
		Object obj = null;
		// 保证工厂的单一性
		if (factory == null) {
			factory = new DigesterFactory();
		}
		Bean bean = factory.doDigester().getBean(id);
		if (bean != null) {
			String className = bean.getType();
			try {
				obj = Class.forName(className).newInstance();
			} catch (InstantiationException e) {
				e.printStackTrace();
			} catch (IllegalAccessException e) {
				e.printStackTrace();
			} catch (ClassNotFoundException e) {
				System.out.println("Not found class named : " + className);
				e.printStackTrace();
			}
		}

		return obj;
	}

}

这里面的写法，与规则，还有方法，可以参照以下去进行学习，这都是对于commons-digester.jar这个包进行的文档：
http://commons.apache.org/digester/

四、然后再看看测试类：

package com.hejianjiao.test;

import com.hejianjiao.digester.DigesterFactory;
import com.hejianjiao.entity.User;

public class Test {

    public static void main(String[] args) {

        User user = (User) DigesterFactory.getObject("user");
        System.out.println(user);

    }

}

package com.hejianjiao.test;

import com.hejianjiao.digester.DigesterFactory;
import com.hejianjiao.entity.User;

public class Test {

	public static void main(String[] args) {

		User user = (User) DigesterFactory.getObject("user");
		System.out.println(user);

	}

}

可以看到，我们可以像工厂模式一样，对想要的bean进行生产。