java 文件 与 base64 之间的转化, 以及 web 实现 base64 上传文件

<1>文件与base64字符串之间的转化

package servlet_file_upload;

import java.io.File;
import java.io.FileInputStream;
import java.io.FileOutputStream;

import sun.misc.BASE64Decoder;
import sun.misc.BASE64Encoder;

/**
 * base64 与 file 之间的相互转化
 * 实现形式, 懒汉式的单例模式
 */
public class Base64UploadClass {
    // 私有化构造器
    private Base64UploadClass() {
    }

    // 事先定义一个变量存放该类的实例
    private static Base64UploadClass fileBase64 = null;

    // 对外暴露一个静态方法获取该类的实例
    public static Base64UploadClass getFileBase64() {
        if (fileBase64 == null) {
            fileBase64 = new Base64UploadClass();
        }
        return fileBase64;
    }

    // 将 file 转化为 Base64
    public String fileToBase64(String path) {
        File file = new File(path);
        FileInputStream inputFile;
        try {
            inputFile = new FileInputStream(file);
            byte[] buffer = new byte[(int) file.length()];
            inputFile.read(buffer);
            inputFile.close();
            return new BASE64Encoder().encode(buffer);
        } catch (Exception e) {
            throw new RuntimeException("文件路径无效
" + e.getMessage());
        }
    }

    // 将 base64 转化为 file
    public boolean base64ToFile(String base64, String path) {
        byte[] buffer;
        try {
            buffer = new BASE64Decoder().decodeBuffer(base64);
            FileOutputStream out = new FileOutputStream(path);
            out.write(buffer);
            out.close();
            return true;
        } catch (Exception e) {
            throw new RuntimeException("base64字符串异常或地址异常
" + e.getMessage());
        }
    }
}

<2> servlet 借助 base64 实现文件上传

package servlet_file_upload;

import java.io.IOException;
import java.net.URLDecoder;

import javax.servlet.ServletException;
import javax.servlet.annotation.WebServlet;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;

@WebServlet("/Base64UploadServlet")
public class Base64UploadServlet extends HttpServlet {
    private static final long serialVersionUID = 1L;

    public Base64UploadServlet() {
        super();
    }

    protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        doGet(request, response);
    }

    protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        // 允许跨域访问,并设置请求编码和输出编码为 UTF-8
        response.addHeader("Access-Control-Allow-Origin", "*");
        response.setCharacterEncoding("UTF-8");
        request.setCharacterEncoding("UTF-8");

        // 获取文件将要保存到的文件夹路径
        String path = getServletContext().getRealPath("");

        // 接收base64文件字符串, 并对文件字符串进行解码
        String fileContent = request.getParameter("file");
        fileContent = URLDecoder.decode(fileContent, "UTF-8");
        
        // 获取文件保存的相对路径
        String returnPath = "Upload/" + System.currentTimeMillis() + "." + fileContent.split("\.")[1];

        // 保存文件返回路径
        Base64UploadClass fileBase64 = Base64UploadClass.getFileBase64();
        if(fileBase64.base64ToFile(fileContent.split("\.")[0], path + returnPath)){
            response.getWriter().write(returnPath);
        } else {
            response.getWriter().write("上传失败");
        }
    }
}

前端代码参考:  http://www.cnblogs.com/lovling/p/6686688.html