Spring BeanUtils组件使用

用于演示的javabean

import java.util.Date;

public class People

    private String name;
    private int age;
    private Date birth;

    public People(String name, int age, Date birth) {
        super();
        this.name = name;
        this.age = age;
        this.birth = birth;
    }

    public People() {
        super();
        // TODO Auto-generated constructor stub
    }

    @Override
    public String toString() {
        return "People [name=" + name + ", age=" + age + ", birth=" + birth + "]";
    }

    public String getName() {
        return name;
    }

    public void setName(String name) {
        this.name = name;
    }

    public int getAge() {
        return age;
    }

    public void setAge(int age) {
        this.age = age;
    }

    public Date getBirth() {
        return birth;
    }

    public void setBirth(Date birth) {
        this.birth = birth;
    }

}

测试（所有测试只与源javabean属性值有关，与目标javabean属性值无关）
当源javabean属性均有值时的目标javabean属性复制情况

@Test
public void springBeanUtilsTest(){
    People oldPeople = new People("oldName",100,new Date());
    People newPeople = new People();

    //BeanUtils.copyProperties(Object source,Object target);    
    BeanUtils.copyProperties(oldPeople, newPeople);

    System.out.println(oldPeople);
    System.out.println(newPeople);
}

输出结果如下

People [name=oldName, age=100, birth=Wed Jul 19 18:46:13 CST 2017]
People [name=oldName, age=100, birth=Wed Jul 19 18:46:13 CST 2017]

---

当源javabean非Date类型的属性值为null时目标javabean属性的复制情况

@Test
public void springBeanUtilsTest(){
    People oldPeople = new People(null,100,new Date());
    People newPeople = new People("newName",20,null);

    //BeanUtils.copyProperties(Object source,Object target);    
    BeanUtils.copyProperties(oldPeople, newPeople);

    System.out.println(oldPeople);
    System.out.println(newPeople);
}

输出结果如下
注意:目标javabean中的非null属性值被覆盖为null了

People [name=null, age=100, birth=Wed Jul 19 19:04:48 CST 2017]
People [name=null, age=100, birth=Wed Jul 19 19:04:48 CST 2017]

---

当源javabean中Date类型的属性值为null时目标javabean中属性值的复制情况

@Test
public void springBeanUtilsTest(){
    People oldPeople = new People("oldName",100,null);
    People newPeople = new People("newName",20,new Date());

    //BeanUtils.copyProperties(Object source,Object target);    
    BeanUtils.copyProperties(oldPeople, newPeople);

    System.out.println(oldPeople);
    System.out.println(newPeople);
}

输出结果如下

People [name=oldName, age=100, birth=null]
People [name=oldName, age=100, birth=null]

---

BeanUtils.copyProperties(Object source,Object target);方法有一个不足的地方，就是当source里的属性对应的属性值为null时，也会覆盖掉target里相同属性名的属性，即使target中该属性值已存在且不为null的属性值，这显然有些不合理，这是我们可以使用它的一个重载方法：

BeanUtils.copyProperties(Object source,Object target, String... ignoreProperties);

最后一个参数的含义是，复制属性值时忽略的属性名称，所有我们只要找出source中属性值为null的属性名称数组即可，方法如下：

/**
 * 
 * @Title: getNullPropertyNames  
 * @Description: 获取一个对象中属性值为null的属性名字符串数组
 * @param source
 * @return
public static String[] getNullPropertyNames (Object source) {
    final BeanWrapper src = new BeanWrapperImpl(source);
    java.beans.PropertyDescriptor[] pds = src.getPropertyDescriptors();

    Set<String> emptyNames = new HashSet<String>();
    for(java.beans.PropertyDescriptor pd : pds) {
        Object srcValue = src.getPropertyValue(pd.getName());
        if (srcValue == null) emptyNames.add(pd.getName());
    }
    String[] result = new String[emptyNames.size()];
    return

测试

@Test
public void copyBeanNotNull(){
    People oldPeople = new People(null, 100, null);
    People newPeople = new People("newName", 20, new Date());

    //BeanUtils.copyProperties(Object source,Object target, String... ignoreProperties);    
    BeanUtils.copyProperties(oldPeople, newPeople, getNullPropertyNames(oldPeople));

    System.out.println(oldPeople);
    System.out.println(newPeople);
    for(String key : getNullPropertyNames(oldPeople)){
        System.out.println(key);
    }
}

输出结果如下

People [name=null, age=100, birth=null]
People [name=newName, age=100, birth=Wed Jul 19 23:31:05 CST 2017]
name