使用反射创建Bean、Spring中是如何根据类名配置创建Bean实例、Java提供了Class类获取类别的字段和方法，包括构造方法

Java提供了Class类，可以通过编程方式获取类别的字段和方法，包括构造方法 

  获取Class类实例的方法：

  类名.class

  实例名.getClass()

  Class.forName(className)

public class RefTest {
	@Test
	public void testRef(){
		//Class cls = RefTest.class;
		//Class.forName("com.jboa.service.RefTest");
		//new RefTest().getClass();
}

Class类中包含getConstructors()、getFields()、getMethods()；

在test写一个测试的实体类：

package com.jboa.service;

public class User {
	private String username;
	private String password;

	public User() {
	}

	public User(String username, String password) {
		super();
		this.username = username;
		this.password = password;
	}

	public String getUsername() {
		return username;
	}

	public void setUsername(String username) {
		this.username = username;
	}

	public String getPassword() {
		return password;
	}

	public void setPassword(String password) {
		this.password = password;
	}

}

Spring中是如何根据类名配置创建Bean实例的呢？下面代码：

package com.jboa.service;

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

import org.junit.Test;

public class RefTest {
	@Test
	public void testRef() throws Exception {
		//Class cls = RefTest.class;
		//Class.forName("com.jboa.service.RefTest");
		//new RefTest().getClass();

		Object obj = getBean("com.jboa.service.User");
		this.setProperty(obj, "username", "admin");
		this.setProperty(obj, "password", "passw");

		User user = (User) obj; //对应ClassPathXmlApplicationContext.getBean(id)
		System.out.println(user.getUsername());
		System.out.println(user.getPassword());
	}

	public Object getBean(String className) throws Exception {
		Class cls = null;
		try {
			cls = Class.forName(className);//对应Spring ->bean -->class
		} catch (ClassNotFoundException e) {
			e.printStackTrace();
			throw new Exception("类错误！");
		}

		Constructor[] cons = null;//得到所有构造器
		try {
			cons = cls.getConstructors();
		} catch (Exception e) {
			e.printStackTrace();
			throw new Exception("构造器错误！");
		}
		if (cons == null || cons.length < 1) {
			throw new Exception("没有默认构造方法！");
		}
		//如果上面没错，就有构造方法

		Constructor defCon = cons[0];//得到默认构造器,第0个是默认构造器，无参构造方法
		Object obj = defCon.newInstance();//实例化，得到一个对象 //Spring - bean -id
		return obj;
	}

	public void setProperty(Object bean, String propertyName, Object propertyValue) throws Exception {
		Class cls = bean.getClass();
		Method[] methods = cls.getMethods();//得到所有方法
		//cls.getFields();//所有公开字段属性
		//注入属性 用户名：admin setUsername();
		// obj username admin
		//String propertyName = "username";//对应 Spring配置文件- property ->name
		//String propertyValue = "admin";//对应：Spring -- property -->ref/value
		for (Method m : methods) {
			if (m.getName().equalsIgnoreCase("set" + propertyName)) {
				//找到方法就注入
				m.invoke(bean, propertyValue);
				break;
			}
		}
	}
}

运行；

参考的bean：

<bean id="employeeAction" class="com.jboa.action.EmployeeAction" scope="prototype">
		<property name="employeeService" ref="employeeService"></property>
		<property name="dictionaryService" ref="dictionaryService"></property>
</bean>