源码分析：Spring 属性设置 - PropertyAccessorFactory

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总结

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一句话：BeanWrapperImpl只可以setter方法注入，DirectFieldAccessor反射属性注入（更强大）
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AbstractNestablePropertyAccessor.setPropertyValue(String, Object)
    // 1. 获取Object
    nestedPa = getPropertyAccessorForPropertyPath(propertyName);
        含有 [ ] .    先取到外层对象， 再递归   例如：friend.name   先拿取到 friend对象，再解析 name属性
                      ===> 默认内层对象不存在，根据 isAutoGrowNestedPaths() 标识创建默认对象
        不含有 [ ] .  直接获取当前对象 
    // 2. 进行setter（不同子类实现）
    nestedPa.setPropertyValue(tokens, new PropertyValue(propertyName, value));
        BeanWrapperImpl        BeanPropertyHandler.setValue
        ---> ReflectionUtils.makeAccessible(writeMethod);
        ---> writeMethod.invoke(getWrappedInstance(), value);
        DirectFieldAccessor    FieldPropertyHandler.setValue
        ---> ReflectionUtils.makeAccessible(this.field);
        ---> this.field.set(getWrappedInstance(), value);
				
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测试代码

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public class MyTest {

    // @Data
    public static class Student {
        public Student() {
            System.out.println("创建了..." + this.hashCode());// 用于debug
        }

        private String name;
        private Integer age;

        private Student friend;
        private List<String> hobbies;
    }

    // 2024-05-08 17:33
    public static void main(String[] args) throws Throwable {
        // Student student = new Student();
        // BeanWrapper beanWrapper = PropertyAccessorFactory.forBeanPropertyAccess(student);
        // beanWrapper.setPropertyValue("name", "陶攀峰");
        // beanWrapper.setPropertyValue("age", 18);
        //
        // beanWrapper.setAutoGrowNestedPaths(true);// friend 属性为null时，自动创建
        //
        // // beanWrapper.setPropertyValue("friend", new Student());
        // beanWrapper.setPropertyValue("friend.name", "二狗");
        // beanWrapper.setPropertyValue("friend.age", 20);
        //
        // // beanWrapper.setPropertyValue("hobbies", new ArrayList<>());
        // beanWrapper.setPropertyValue("hobbies[0]", "a");
        // beanWrapper.setPropertyValue("hobbies[1]", "b");
        // beanWrapper.setPropertyValue("hobbies[2]", "c");
        // System.out.println(student);
        //-----------------------------------------------------------------------------
        Student student = new Student();
        ConfigurablePropertyAccessor accessor = PropertyAccessorFactory.forDirectFieldAccess(student);
        accessor.setPropertyValue("name", "陶攀峰");
        accessor.setPropertyValue("age", 18);

        accessor.setAutoGrowNestedPaths(true);// friend 属性为null时，自动创建

        // accessor.setPropertyValue("friend", new Student());
        accessor.setPropertyValue("friend.name", "二狗");
        accessor.setPropertyValue("friend.age", 20);

        // accessor.setPropertyValue("hobbies", new ArrayList<>());
        accessor.setPropertyValue("hobbies[0]", "a");
        accessor.setPropertyValue("hobbies[1]", "b");
        accessor.setPropertyValue("hobbies[2]", "c");
        System.out.println(student);
    }
}