Java-time reading or writing the file contents

1. Problem demand

The actual project, there are many cases need to read the contents of the file into memory one time, some of the processing business, here to give a simple case

import java.io.File;
import java.io.FileWriter;
import java.io.Writer;
import java.io.IOException;
import java.io.FileInputStream;

public class Deletekey {
	
	public static String readFile(File file) throws IOException {
		if (file != null && file.canRead()){
	        byte[] bytes = new byte[(int) file.length()];
	        FileInputStream fileInputStream = new FileInputStream(file);
	        fileInputStream.read(bytes);
	        String content = new String(bytes,"UTF-8");
	        fileInputStream.close();
	        return content;
		}
		return "";
	}

	public static void saveFile(StringBuilder string,File file)throws IOException{
			Writer writer = new FileWriter(file);
			writer.write(string.toString());
			writer.close();
	}
	
	public static void main(String[] args) throws IOException {
		File file = new File(System.getProperty("user.dir")+ "\\paper.txt");
		StringBuilder OrignText = new StringBuilder(readFile(file));
		
		System.out.println(OrignText);

		File fileout = new File("NoKeyPaper.txt");
		saveFile(OrignText,fileout);
	}
}

Here is my reference to the two codes, from https://blog.csdn.net/testcs_dn/article/details/41982939

import java.io.*;
 
/**
 * @Author ：feiyang
 * @Date ：Created 2019/5/15
 */
public class ReadFileUtil {
 
    public String acceptFile(String filePath) throws IOException {
        File file = new File(filePath);
        byte[] bytes = new byte[(int) file.length()];
        FileInputStream fileInputStream = new FileInputStream(filePath);
        int ret  = fileInputStream.read(bytes);
        String content = new String(bytes, 0, ret);
        return content;
    }
}

public class IOHelper {
 
	public static void copy(Reader in,Writer out) throws IOException {
		int c = -1;
		while((c = in.read()) != -1) {
			out.write(c);
		}
	}
	
	public static String readFile(File file) throws IOException {
		if (file != null && file.canRead()){
			Reader in = new FileReader(file);
			StringWriter out = new StringWriter();
			copy(in,out);
			return out.toString();
		}
		return "";
	}
	
	public static void saveFile(File file,String content) throws IOException {
		Writer writer = new FileWriter(file);
		writer.write(content);
		writer.close();
	}	
}