JavaWeb-spring

Java反射机制

import java.lang.reflect.Constructor;
import java.lang.reflect.Method;

public class ReflectTest {

    public static Car  initByDefaultConst() throws Throwable
    {
        //1.通过类装载器获取Car类对象
        ClassLoader loader = Thread.currentThread().getContextClassLoader();
        Class clazz = loader.loadClass("com.jike.spring.chapter03.reflect.Car");

        //2.获取类的默认构造器对象并实例化Car
        Constructor cons = clazz.getDeclaredConstructor((Class[])null);
        Car car = (Car)cons.newInstance();

        //3.通过反射方法设置属性
        Method setBrand = clazz.getMethod("setBrand",String.class);
        setBrand.invoke(car,"奔驰");
        Method setColor = clazz.getMethod("setColor",String.class);
        setColor.invoke(car,"黑色");
        Method setMaxSpeed = clazz.getMethod("setMaxSpeed",int.class);
        setMaxSpeed.invoke(car,200);
        return car;
    }

    public static Car initByParamConst()  throws Throwable{
        //1.通过类装载器获取Car类对象
        ClassLoader loader = Thread.currentThread().getContextClassLoader();
        Class clazz = loader.loadClass("com.jike.spring.chapter03.reflect.Car");

        //2.获取类的带有参数的构造器对象
        Constructor cons = clazz.getDeclaredConstructor(new Class[]{String.class,String.class,int.class});

        //3.使参数的构造器对象实例化Car
        Car car = (Car)cons.newInstance(new Object[]{"宝马","红色",180});
        return car;
    }

    public static void main(String[] args) throws Throwable {
        Car car1 = initByDefaultConst();
        Car car2 = initByParamConst();
        car1.introduce();
        car2.introduce();
    }
}

Car类
public class Car {
private String brand;

private String color;

private int maxSpeed;

//1.默认构造函数
public Car(){
System.out.println("init car!!");
}

//2.带参构造函数
public Car(String brand,String color,int maxSpeed){
this.brand = brand;
this.color = color;
this.maxSpeed = maxSpeed;
}

//3.未带参的方法
public void introduce() {
System.out.println("brand:"+brand+";color:"+color+";maxSpeed:"+maxSpeed);
}

public String getBrand() {
return brand;
}

public void setBrand(String brand) {
this.brand = brand;
}

public String getColor() {
return color;
}

public void setColor(String color) {
this.color = color;
}

public int getMaxSpeed() {
return maxSpeed;
}

public void setMaxSpeed(int maxSpeed) {
this.maxSpeed = maxSpeed;
}
}

XML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"
    xmlns:util="http://www.springframework.org/schema/util"
    xmlns:p="http://www.springframework.org/schema/p"
    xsi:schemaLocation="http://www.springframework.org/schema/beans
     http://www.springframework.org/schema/beans/spring-beans-3.0.xsd
     http://www.springframework.org/schema/util
    http://www.springframework.org/schema/util/spring-util-4.1.xsd">
    <bean class="com.spring.study04.HelloWordImp" />
</beans>

BeanFactory代码

import java.io.InputStream;
import java.lang.reflect.Method;
import java.util.HashMap;
import java.util.Iterator;
import java.util.Map;

import org.dom4j.Attribute;
import org.dom4j.Document;
import org.dom4j.Element;
import org.dom4j.io.SAXReader;

public class BeanFactory {

    private Map<String, Object> beanMap = new HashMap<String, Object>();

    /**
     * bean工厂的初始化.
     *
     * @param xml xml配置文件
     */
    public void init(String xml) {
        try {
            //1.创建读取配置文件的reader对象
            SAXReader reader = new SAXReader();

            //2.获取当前线程中的类装载器对象
            ClassLoader classLoader = Thread.currentThread().getContextClassLoader();

            //3.从class目录下获取指定的xml文件
            InputStream ins = classLoader.getResourceAsStream(xml);
            Document doc = reader.read(ins);
            Element root = doc.getRootElement();
            Element foo;

            //4.遍历xml文件当中的Bean实例
            for (Iterator i = root.elementIterator("bean"); i.hasNext();) {
                foo = (Element) i.next();

                //5.针对每个一个Bean实例，获取bean的属性id和class
                Attribute id = foo.attribute("id");
                Attribute cls = foo.attribute("class");

                //6.利用Java反射机制，通过class的名称获取Class对象
                Class bean = Class.forName(cls.getText());
                //7.获取对应class的信息
                java.beans.BeanInfo info = java.beans.Introspector.getBeanInfo(bean);
                //8.获取其属性描述
                java.beans.PropertyDescriptor pd[] = info.getPropertyDescriptors();

                //9.创建一个对象，并在接下来的代码中为对象的属性赋值
                Object obj = bean.newInstance();

                //10.遍历该bean的property属性
                for (Iterator ite = foo.elementIterator("property"); ite.hasNext();) {
                    Element foo2 = (Element) ite.next();

                    //11.获取该property的name属性
                    Attribute name = foo2.attribute("name");
                    String value = null;

                    //12.获取该property的子元素value的值
                    for (Iterator ite1 = foo2.elementIterator("value"); ite1.hasNext();)
                    {
                        Element node = (Element) ite1.next();
                        value = node.getText();
                        break;
                    }

                    //13.利用Java的反射机制调用对象的某个set方法，并将值设置进去
                    for (int k = 0; k < pd.length; k++) {
                        if (pd[k].getName().equalsIgnoreCase(name.getText()))
                        {
                            Method mSet = null;
                            mSet = pd[k].getWriteMethod();
                            mSet.invoke(obj, value);
                        }
                    }
                }

                //14.将对象放入beanMap中，其中key为id值，value为对象
                beanMap.put(id.getText(), obj);
            }
        } catch (Exception e) {
            System.out.println(e.toString());
        }
    }

    /**
     * 通过bean的id获取bean的对象.
     *
     * @param beanName
     *            bean的id
     * @return 返回对应对象
     */
    public Object getBean(String beanName) {
        Object obj = beanMap.get(beanName);
        return obj;
    }

    /**
     * 测试方法.
     *
     * @param args
     */
    public static void main(String[] args) {
        BeanFactory factory = new BeanFactory();
        factory.init("conf/config.xml");
        JavaBean javaBean = (JavaBean) factory.getBean("javaBean");
        System.out.println("userName=" + javaBean.getUserName());
        System.out.println("password=" + javaBean.getPassword());
    }
}