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>