BeanUtils.populate 使用笔记

大家好，又见面了，我是你们的朋友全栈君。

最近在学习网站开发，在后端获取网站请求数据的时候用到了BeanUtils.populate（）方法，具体用法是：

BeanUtils.populate(object obj, Map<String, String[]> map);

于是我就在想这个方法是怎么把map中的数据封装到obj对象里的。打开源码看，看别人写的代码是真难受，看了半天还是没看懂。上网搜了一下，发现多数都是在讲用法，关于方法的实现过程一部分人是说obj对象里要有名称与map中key对应的成员变量，另一部分说是要有与key对应的set方法，讲得都不太明白。

自己动手，丰衣足食。写几个类测试下，上代码。先构建4个Student对象：

StudentA.java

/* * 有r成员，方法各自对应 */
public class StudentA { 
   
	private String name;
	private String number;
	private String sex;
	private String r_name;
	private String r_number;
	private String r_sex;
	
	
	
	public String getName() { 
   
		return name;
	}
	public void setName(String name) { 
   
		this.name = name;
	}
	public String getNumber() { 
   
		return number;
	}
	public void setNumber(String number) { 
   
		this.number = number;
	}
	public String getSex() { 
   
		return sex;
	}
	public void setSex(String sex) { 
   
		this.sex = sex;
	}

	public String getR_name() { 
   
		return r_name;
	}
	public void setR_name(String r_name) { 
   
		this.r_name = r_name;
	}
	public String getR_number() { 
   
		return r_number;
	}
	public void setR_number(String r_number) { 
   
		this.r_number = r_number;
	}
	public String getR_sex() { 
   
		return r_sex;
	}
	public void setR_sex(String r_sex) { 
   
		this.r_sex = r_sex;
	}
	
	
	public StudentA() { 
   
		super();
	}
	
	public StudentA(String name, String number, String sex) { 
   
		super();
		this.name = name;
		this.number = number;
		this.sex = sex;
	}
	
}

StudentB.java

/* * 有r成员，但r方法对应到不带r成员上 */
public class StudentB { 
   
	private String name;
	private String number;
	private String sex;
	private String r_name;
	private String r_number;
	private String r_sex;
	
	
	
	public String getName() { 
   
		return name;
	}
	public void setName(String name) { 
   
		this.name = name;
	}
	public String getNumber() { 
   
		return number;
	}
	public void setNumber(String number) { 
   
		this.number = number;
	}
	public String getSex() { 
   
		return sex;
	}
	public void setSex(String sex) { 
   
		this.sex = sex;
	}
	
	public String getR_name() { 
   
		return name;
	}
	public void setR_name(String r_name) { 
   
		this.name = r_name;
	}
	public String getR_number() { 
   
		return number;
	}
	public void setR_number(String r_number) { 
   
		this.number = r_number;
	}
	public String getR_sex() { 
   
		return sex;
	}
	public void setR_sex(String r_sex) { 
   
		this.sex = r_sex;
	}
	
	public String sysNa() { 
   
		return r_name;
	}
	public String sysNu() { 
   
		return r_number;
	}
	public String sysSe() { 
   
		return r_sex;
	}
	
	
	public StudentB() { 
   
		super();
	}
	
	public StudentB(String name, String number, String sex) { 
   
		super();
		this.name = name;
		this.number = number;
		this.sex = sex;
	}

}

StudentC.java

/* * 无r成员，但有r方法且对应到不带r成员上 */
public class StudentC { 
   
	private String name;
	private String number;
	private String sex;
	/* * private String r_name; private String r_number; private String r_sex; */
	
	
	
	public String getName() { 
   
		return name;
	}
	public void setName(String name) { 
   
		this.name = name;
	}
	public String getNumber() { 
   
		return number;
	}
	public void setNumber(String number) { 
   
		this.number = number;
	}
	public String getSex() { 
   
		return sex;
	}
	public void setSex(String sex) { 
   
		this.sex = sex;
	}
	public String getR_name() { 
   
		return name;
	}
	public void setR_name(String r_name) { 
   
		this.name = r_name;
	}
	public String getR_number() { 
   
		return number;
	}
	public void setR_number(String r_number) { 
   
		this.number = r_number;
	}
	public String getR_sex() { 
   
		return sex;
	}
	public void setR_sex(String r_sex) { 
   
		this.sex = r_sex;
	}
	
	
	public StudentC() { 
   
		super();
	}
	
	public StudentC(String name, String number, String sex) { 
   
		super();
		this.name = name;
		this.number = number;
		this.sex = sex;
	}

}

StudentD.java

/* * 有r成员，但没有对应的set和get的r方法 */
public class StudentD { 
   
	private String name;
	private String number;
	private String sex;
	private String r_name;
	private String r_number;
	private String r_sex;
	
	
	public String getName() { 
   
		return name;
	}
	public void setName(String name) { 
   
		this.name = name;
	}
	public String getNumber() { 
   
		return number;
	}
	public void setNumber(String number) { 
   
		this.number = number;
	}
	public String getSex() { 
   
		return sex;
	}
	public void setSex(String sex) { 
   
		this.sex = sex;
	}
	
	public String sysNa() { 
   
		return r_name;
	}
	public String sysNu() { 
   
		return r_number;
	}
	public String sysSe() { 
   
		return r_sex;
	}
	
	
	public StudentD() { 
   
		super();
	}
	public StudentD(String name, String number, String sex) { 
   
		super();
		this.name = name;
		this.number = number;
		this.sex = sex;
	}
	
}

BeanUtils.populate() 方法测试类：

BeanUtilsTest.java

public class BeanUtilsTest { 
   

	public static void main(String[] args) { 
   
		StudentA studenta = new StudentA();
		StudentB studentb = new StudentB();
		StudentC studentc = new StudentC();
		StudentD studentd = new StudentD();
		
		Map<String, String> map = new HashMap<String, String>();
		map.put("r_name", "xiaoming");
		map.put("r_number", "1600890105");
		map.put("r_sex", "boy");
		
		//map测试代码块
		{ 
   	// 遍历Map是否有值
			System.out.println("Map遍历开始：{");
			for (Entry<String, String> entry : map.entrySet()) { 
   
				System.out.println(" " + entry.getKey() + "：" + entry.getValue());
			}
			System.out.println(" }\n");
		}

		//使用BeanUtils将 map的值封装到 student对象
		try { 
   
			BeanUtils.populate(studenta, map);
			BeanUtils.populate(studentb, map);
			BeanUtils.populate(studentc, map);
			BeanUtils.populate(studentd, map);
		} catch (IllegalAccessException e) { 
   
			e.printStackTrace();
		} catch (InvocationTargetException e) { 
   
			e.printStackTrace();
		}
		
		//检测封装结果
		System.out.println("stundenta对象（成员与各自方法对应）：");
		System.out.println(" 姓名：" + studenta.getName());
		System.out.println(" 学号：" + studenta.getNumber());
		System.out.println(" 性别：" + studenta.getSex());
		System.out.println(" r_name：" + studenta.getR_name());
		System.out.println(" r_number：" + studenta.getR_number());
		System.out.println(" r_sex：" + studenta.getR_sex());
		System.out.println();
		
		System.out.println("stundentb对象（有r成员，但r方法对应到不带r成员上）：");
		System.out.println(" 姓名：" + studentb.getName());
		System.out.println(" 学号：" + studentb.getNumber());
		System.out.println(" 性别：" + studentb.getSex());
		System.out.println(" r_name：" + studentb.sysNa());
		System.out.println(" r_number：" + studentb.sysNu());
		System.out.println(" r_sex：" + studentb.sysSe());
		System.out.println();
		
		System.out.println("stundentc对象（无r成员，但有r方法且对应到不带r的成员上）：");
		System.out.println(" 姓名：" + studentc.getName());
		System.out.println(" 学号：" + studentc.getNumber());
		System.out.println(" 性别：" + studentc.getSex());
		System.out.println(" r_name：" + studentc.getR_name());
		System.out.println(" r_number：" + studentc.getR_number());
		System.out.println(" r_sex：" + studentc.getR_sex());
		System.out.println();

		System.out.println("stundentd对象（有r成员，但没有r方法）：");
		System.out.println(" 姓名：" + studentc.getName());
		System.out.println(" 学号：" + studentc.getNumber());
		System.out.println(" 性别：" + studentc.getSex());
		System.out.println(" r_name：" + studentd.sysNa());
		System.out.println(" r_number：" + studentd.sysNu());
		System.out.println(" r_sex：" + studentd.sysSe());
		System.out.println();
	}

}

测试结果：

Map遍历开始：{ 
   
   r_number：1600890105
   r_sex：boy
   r_name：xiaoming
 }

stundenta对象（成员与各自方法对应）：
  姓名：null
  学号：null
  性别：null
 r_name：xiaoming
 r_number：1600890105
 r_sex：boy

stundentb对象（有r成员，但r方法对应到不带r成员上）：
  姓名：xiaoming
  学号：1600890105
  性别：boy
 r_name：null
 r_number：null
 r_sex：null

stundentc对象（无r成员，但有r方法且对应到不带r的成员上）：
  姓名：xiaoming
  学号：1600890105
  性别：boy
 r_name：xiaoming
 r_number：1600890105
 r_sex：boy

stundentd对象（有r成员，但没有r方法）：
  姓名：null
  学号：null
  性别：null
 r_name：null
 r_number：null
 r_sex：null

结论：由测试结果可见，BeanUtils.populate() 方法的实现过程是通过 obj对象中与map中 key对应的 set方法来实现封装，与obj对象中是否存在名称与 map中key对的成员变量无关。当然，这只是针对BeanUtils.populate(object obj, Map<String, String[]> map)的用法的结论。

仔细一想，对象的所有成员变量都是私有的，在对象范围外根本无法在直接对成员变量赋值，也只有用对应的set方法，真是为自己智商感到捉急。