java实现文件发送

关于#java#的问题：Java如何实现本地上传和向客户发送？在线提问，有人给解说一下吗

import org.springframework.web.bind.annotation.RequestMapping;
import org.springframework.web.bind.annotation.RequestMethod;
import org.springframework.web.context.ContextLoader;

import javax.servlet.ServletOutputStream;
import javax.servlet.http.HttpServletResponse;
import java.io.*;
import java.net.HttpURLConnection;
import java.net.URL;
import java.net.URLEncoder;
import java.util.UUID;

public class FileUtil {

/**
 * 上传文件
 *
 * @param file
 * @param filePath
 * @param fileName
 * @throws Exception
 */
public static void uploadFile(byte[] file, String filePath, String fileName) throws Exception {
    File targetFile = new File(filePath);
    if (!targetFile.exists()) {
        targetFile.mkdirs();
    }
    FileOutputStream out = new FileOutputStream(filePath + fileName);
    out.write(file);
    out.flush();
    out.close();
}

/**
 * 判断文件是否存在
 *
 * @param filePath
 * @throws Exception
 */
public static boolean exists(String filePath) {
    File targetFile = new File(filePath);
    return targetFile.exists();
}

/**
 * 删除文件
 *
 * @param fileName
 * @return
 */
public static boolean deleteFile(String fileName) {
    File file = new File(fileName);
    // 如果文件路径所对应的文件存在，并且是一个文件，则直接删除
    if (file.exists() && file.isFile()) {
        if (file.delete()) {
            return true;
        } else {
            return false;
        }
    } else {
        return false;
    }
}

public static String renameToUUID(String fileName) {
    return UUID.randomUUID() + "." + fileName.substring(fileName.lastIndexOf(".") + 1);
}

public static void download(HttpServletResponse res, String path, String fileName) {
    downloadLocal(res, path, fileName);
}

/**
 * 下载本地文件
 *
 * @param response
 * @param path
 * @param fileName
 */
public static void downloadLocal(HttpServletResponse response, String path, String fileName) {
    FileInputStream fileIn = null;
    ServletOutputStream out = null;
    try {
        //String fileName = new String(fileNameString.getBytes("ISO8859-1"), "UTF-8");
        response.setContentType("application/octet-stream");
        // URLEncoder.encode(fileNameString, "UTF-8") 下载文件名为中文的，文件名需要经过url编码
        response.setHeader("Content-Disposition", "attachment;filename=" + URLEncoder.encode(fileName, "UTF-8"));
        File file;
        String filePathString = path + fileName;
        file = new File(filePathString);
        fileIn = new FileInputStream(file);
        out = response.getOutputStream();

        byte[] outputByte = new byte[1024];
        int readTmp = 0;
        while ((readTmp = fileIn.read(outputByte)) != -1) {
            out.write(outputByte, 0, readTmp); //并不是每次都能读到1024个字节，所有用readTmp作为每次读取数据的长度，否则会出现文件损坏的错误
        }
    } catch (Exception e) {
        //log.error(e.getMessage());
        e.printStackTrace();
    } finally {
        try {
            fileIn.close();
            out.flush();
            out.close();
        } catch (IOException e) {
            e.printStackTrace();
        }
    }
}


/**
 * 下载网络文件
 *
 * @param fileUrl
 * @param fileLocal
 * @return
 * @throws Exception
 */
public static boolean downloadNet(String fileUrl, String fileLocal) throws Exception {
    boolean flag = false;
    URL url = new URL(fileUrl);
    HttpURLConnection urlCon = (HttpURLConnection) url.openConnection();
    urlCon.setConnectTimeout(6000);
    urlCon.setReadTimeout(6000);
    int code = urlCon.getResponseCode();
    if (code != HttpURLConnection.HTTP_OK) {
        throw new Exception("文件读取失败");
    }
    //读文件流
    DataInputStream in = new DataInputStream(urlCon.getInputStream());
    DataOutputStream out = new DataOutputStream(new FileOutputStream(fileLocal));
    byte[] buffer = new byte[2048];
    int count = 0;
    while ((count = in.read(buffer)) > 0) {
        out.write(buffer, 0, count);
    }
    try {
        if (out != null) {
            out.close();
        }
        if (in != null) {
            in.close();
        }

    } catch (Exception e) {
        e.printStackTrace();
    }
    flag = true;
    return flag;
}

}