BeanUtils是如何複製Bean的

BeanUtils在pom中需要增加

    <dependency>
      <groupId>org.springframework</groupId>
      <artifactId>spring-beans</artifactId>
      <version>5.1.9.RELEASE</version>
    </dependency>

上代碼

import org.springframework.beans.BeanUtils;

public class SpringUtilCopyTest {
    public static  void main(String args[]){
        Person  person= new Person();
        Teacher teacher= new Teacher();
        teacher.setAge("11");
        teacher.setName("notall");
        teacher.setSchool("guangming");
        Student student= new Student();
        student.setAge(99);
        student.setId("120");
        student.setHome("noway");
        BeanUtils.copyProperties(teacher,person);
        System.out.println(person.toString());
        BeanUtils.copyProperties(student,person);
        System.out.println(person.toString());
    }
}
class Person{
    String name;
    String age;
    String id;
    String home;
    int myid;

    public int getMyid() {
        return myid;
    }

    public void setMyid(int myid) {
        this.myid = myid;
    }

    @Override
    public String toString() {
        return "Person{" +
                "name='" + name + '\'' +
                ", age='" + age + '\'' +
                ", id='" + id + '\'' +
                ", home='" + home + '\'' +
                ", myid=" + myid +
                '}';
    }

    public String getName() {
        return name;
    }

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

    public String getAge() {
        return age;
    }

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

    public String getId() {
        return id;
    }

    public void setId(String id) {
        this.id = id;
    }

    public String getHome() {
        return home;
    }

    public void setHome(String home) {
        this.home = home;
    }
}
class Teacher{
    String school;
    String name;
    String age;

    public String getSchool() {
        return school;
    }

    public void setSchool(String school) {
        this.school = school;
    }

    public String getName() {
        return name;
    }

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

    public String getAge() {
        return age;
    }

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

class Student{
    String id;
    int age;
    String home;

    public String getHome() {
        return home;
    }

    public void setHome(String home) {
        this.home = home;
    }

    public String getId() {
        return id;
    }

    public void setId(String id) {
        this.id = id;
    }

    public int getAge() {
        return age;
    }

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

運行結果

Person{name=‘notall’, age=‘11’, id=‘null’, home=‘null’, myid=0}
Person{name=‘notall’, age=‘11’, id=‘120’, home=‘noway’, myid=0}

結論

1.多個類複製到同一個類的時候，類型不同不會衝突。
2.同類型同名的參數， 一旦賦值 不再重複賦值
3.沒有同類型同名參數，不會被賦值，因此可能有參數爲空。

原理

```markup

```java
在這裏插入代碼片
    public static void copyProperties(Object source, Object target) throws BeansException {
        copyProperties(source, target, (Class)null, (String[])null);
    }```
   private static void copyProperties(Object source, Object target, @Nullable Class<?> editable, @Nullable String... ignoreProperties) throws BeansException {
        Assert.notNull(source, "Source must not be null");
        Assert.notNull(target, "Target must not be null");
        Class<?> actualEditable = target.getClass();
        if (editable != null) {
            if (!editable.isInstance(target)) {
                throw new IllegalArgumentException("Target class [" + target.getClass().getName() + "] not assignable to Editable class [" + editable.getName() + "]");
            }

            actualEditable = editable;
        }

        PropertyDescriptor[] targetPds = getPropertyDescriptors(actualEditable);
        List<String> ignoreList = ignoreProperties != null ? Arrays.asList(ignoreProperties) : null;
        PropertyDescriptor[] var7 = targetPds;
        int var8 = targetPds.length;

        for(int var9 = 0; var9 < var8; ++var9) {
            PropertyDescriptor targetPd = var7[var9];
            Method writeMethod = targetPd.getWriteMethod();
            if (writeMethod != null && (ignoreList == null || !ignoreList.contains(targetPd.getName()))) {
                PropertyDescriptor sourcePd = getPropertyDescriptor(source.getClass(), targetPd.getName());
                if (sourcePd != null) {
                    Method readMethod = sourcePd.getReadMethod();
                    if (readMethod != null && ClassUtils.isAssignable(writeMethod.getParameterTypes()[0], readMethod.getReturnType())) {
                        try {
                            if (!Modifier.isPublic(readMethod.getDeclaringClass().getModifiers())) {
                                readMethod.setAccessible(true);
                            }

                            Object value = readMethod.invoke(source);
                            if (!Modifier.isPublic(writeMethod.getDeclaringClass().getModifiers())) {
                                writeMethod.setAccessible(true);
                            }

                            writeMethod.invoke(target, value);
                        } catch (Throwable var15) {
                            throw new FatalBeanException("Could not copy property '" + targetPd.getName() + "' from source to target", var15);
                        }
                    }
                }
            }
        }

    }

注意以下代碼

```java
if (readMethod != null && ClassUtils.isAssignable(writeMethod.getParameterTypes()[0], readMethod.getReturnType())) {
                        try {
                            if (!Modifier.isPublic(readMethod.getDeclaringClass().getModifiers())) {
                                readMethod.setAccessible(true);
                            }

                            Object value = readMethod.invoke(source);
                            if (!Modifier.isPublic(writeMethod.getDeclaringClass().getModifiers())) {
                                writeMethod.setAccessible(true);
                            }

                            writeMethod.invoke(target, value);
                        } catch (Throwable var15) {
                            throw new FatalBeanException("Could not copy property '" + targetPd.getName() + "' from source to target", var15);
                        }
                    }