需要:
根据文件全路径读取文件中的内容

package data.test.demo;

import java.io.BufferedReader;
import java.io.File;
import java.io.FileInputStream;
import java.io.InputStreamReader;

public class Test {
	
	public static void main(String[] args) {
		
		String fullFilePath = "D:\\test\\a.txt";
		String base64Image = readFileByPath(fullFilePath);
		System.out.println(base64Image);

	}
	public static String readFileByPath(String fullFilePath) {
        StringBuilder result = new StringBuilder();
        try {
        	File file = new File(fullFilePath);
        	FileInputStream fileInputStream = new FileInputStream(file);
        	InputStreamReader inputStreamReader = new InputStreamReader(fileInputStream, "UTF-8");
            BufferedReader bufferedReader = new BufferedReader(inputStreamReader);
            String line = null;
            while ((line = bufferedReader.readLine()) != null) {
                result.append(line);
            }
            bufferedReader.close();
        } catch (Exception e) {
            e.printStackTrace();
        }
        return result.toString();
    }

	
}