Spring set java.io.File property use java.lang.String bean

I found a strange thing while learning Spring tech.

I inject a java.lang.String type bean into a bean property which type is java.io.File, but the program still runs normally.

I want to know

1. What happened internally?
2. Is it a valid usage or a trick?

Here is the spring configuration file stringtofile.xml.

<?xml version="1.0" encoding="UTF-8"?>
<beans xmlns="http://www.springframework.org/schema/beans"
       xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
       xmlns:c="http://www.springframework.org/schema/c"
       xmlns:p="http://www.springframework.org/schema/p"
       xsi:schemaLocation="http://www.springframework.org/schema/beans
    http://www.springframework.org/schema/beans/spring-beans-4.0.xsd"
       default-lazy-init="true">

    <bean id="file_str"
          class="java.lang.String"
          c:_="C:\tmp\test.hi"/>

    <bean id="file"
          class="stringtofile.FileWrapper"
          p:file-ref="file_str"/>
</beans>

Here is my test classes.

package stringtofile;

import org.springframework.context.ApplicationContext;
import org.springframework.context.support.ClassPathXmlApplicationContext;

import java.io.File;

public class FileWrapper {
    File file;

    public File getFile() {
        return file;
    }

    public FileWrapper setFile(File file) {
        this.file = file;
        return this;
    }

    public static void main(String[] args) {
        ApplicationContext ctx =
                new ClassPathXmlApplicationContext("stringtofile.xml");
        FileWrapper fileWrapper =
                (FileWrapper) ctx.getBean("file");
        System.out.println(fileWrapper.getFile());
    }
}