Java 下载文件的方法怎么写

参考下面

public HttpServletResponse download(String path, HttpServletResponse response) {

try {

// path是指欲下载的文件的路径。

File file = new File(path)

// 取得文件名。

String filename = file.getName()

// 取得文件的后缀名。

String ext = filename.substring(filename.lastIndexOf(".") + 1).toUpperCase()

// 以流的形式下载文件。

InputStream fis = new BufferedInputStream(new FileInputStream(path))

byte[] buffer = new byte[fis.available()]

fis.read(buffer)

fis.close()

// 清空response

response.reset()

// 设置response的Header

response.addHeader("Content-Disposition", "attachmentfilename=" + new String(filename.getBytes()))

response.addHeader("Content-Length", "" + file.length())

OutputStream toClient = new BufferedOutputStream(response.getOutputStream())

response.setContentType("application/octet-stream")

toClient.write(buffer)

toClient.flush()

toClient.close()

} catch (IOException ex) {

ex.printStackTrace()

}

return response

}

// 下载本地文件

public void downloadLocal(HttpServletResponse response) throws FileNotFoundException {

String fileName = "Operator.doc".toString()// 文件的默认保存名

// 读到流中

InputStream inStream = new FileInputStream("c:/Operator.doc")// 文件的存放路径

// 设置输出的格式

response.reset()

response.setContentType("bin")

response.addHeader("Content-Disposition", "attachmentfilename=\"" + fileName + "\"")

// 循环取出流中的数据

byte[] b = new byte[100]

int len

try {

while ((len = inStream.read(b)) >0)

response.getOutputStream().write(b, 0, len)

inStream.close()

} catch (IOException e) {

e.printStackTrace()

}

}

// 下载网络文件

public void downloadNet(HttpServletResponse response) throws MalformedURLException {

int bytesum = 0

int byteread = 0

URL url = new URL("windine.blogdriver.com/logo.gif")

try {

URLConnection conn = url.openConnection()

InputStream inStream = conn.getInputStream()

FileOutputStream fs = new FileOutputStream("c:/abc.gif")

byte[] buffer = new byte[1204]

int length

while ((byteread = inStream.read(buffer)) != -1) {

bytesum += byteread

System.out.println(bytesum)

fs.write(buffer, 0, byteread)

}

} catch (FileNotFoundException e) {

e.printStackTrace()

} catch (IOException e) {

e.printStackTrace()

}

}

//支持在线打开文件的一种方式

public void downLoad(String filePath, HttpServletResponse response, boolean isOnLine) throws Exception {

File f = new File(filePath)

if (!f.exists()) {

response.sendError(404, "File not found!")

return

}

BufferedInputStream br = new BufferedInputStream(new FileInputStream(f))

byte[] buf = new byte[1024]

int len = 0

response.reset()// 非常重要

if (isOnLine) { // 在线打开方式

URL u = new URL("file:///" + filePath)

response.setContentType(u.openConnection().getContentType())

response.setHeader("Content-Disposition", "inlinefilename=" + f.getName())

// 文件名应该编码成UTF-8

} else { // 纯下载方式

response.setContentType("application/x-msdownload")

response.setHeader("Content-Disposition", "attachmentfilename=" + f.getName())

}

OutputStream out = response.getOutputStream()

while ((len = br.read(buf)) >0)

out.write(buf, 0, len)

br.close()

out.close()

}

通常可以直接通过FTPClient 工具类下载文件到本地的，可以通过ByteArrayOutputStream进行流的读取输出。

/**

*下载文件

*

* @param fileName

* @param date

* @param plainFilePath 明文文件路径路径

* @param filepath

* @return

* @throws Exception

*/

public static String encodeAESFileDownloadByFtp(String plainFilePath, String fileName, String date,String filepath) throws Exception {

FileInputStream fis = null

ByteArrayOutputStream bos = null

FileOutputStream fos = null

FTPClient ftpClient = new FTPClient()

String bl = "false"

try {

//Log.info("下载并解密文件开始")

Log.info("连接远程下载服务器"+CMBCUtil.CMBCHOSTNAME+":"+2021)

ftpClient.connect(CMBCUtil.CMBCHOSTNAME, 2021)

ftpClient.login(CMBCUtil.CMBCLOGINNAME, CMBCUtil.CMBCLOGINPASSWORD)

FTPFile[] fs

fs = ftpClient.listFiles()

for (FTPFile ff : fs) {

if (ff.getName().equals(filepath)) {

ftpClient.changeWorkingDirectory("/"+filepath+"/")

}

}

fs = ftpClient.listFiles()

for (FTPFile ff : fs) {

if (ff.getName().equals(date)) {

bl = "true"

ftpClient.changeWorkingDirectory("/"+filepath+"/" + date)

}

}

Log.info("检查文件路径是否存在：/"+filepath+"/"+date + " "+ bl)

if("false".equals(bl)){

ViewUtil.dataSEErrorPerformedCommon( "查询文件路径不存在："+"/"+filepath+"/" + date)

return bl

}

bl = "false"

fs = ftpClient.listFiles()

for (FTPFile ff : fs) {

if (ff.getName().equals(fileName)) {

bl = "true"

Log.info("下载并解密文件开始。")

fos = new FileOutputStream(plainFilePath)

ftpClient.setBufferSize(1024)

// 设置文件类型（二进制）

ftpClient.setFileType(FTPClient.BINARY_FILE_TYPE)

InputStream is = ftpClient.retrieveFileStream(fileName)

bos = new ByteArrayOutputStream(is.available())

byte[] buffer = new byte[1024]

int count = 0

while ((count = is.read(buffer)) != -1) {

bos.write(buffer, 0, count)

}

bos.flush()

byte[] bytes = decodeAES(key, bos.toByteArray())

fos = new FileOutputStream(plainFilePath)

fos.write(bytes)

Log.info("下载并解密文件结束："+plainFilePath)

}

}

Log.info("检查文件是否存："+fileName+" "+bl)

if("false".equals(bl)){

ViewUtil.dataSEErrorPerformedCommon("查询无结果，请稍后再查询。")

return bl

}

return bl

} catch (Exception e) {

throw e

} finally {

if (fis != null) {

try {

fis.close()

} catch (Exception e) {

Log.info(e.getLocalizedMessage(), e)

}

}

if (bos != null) {

try {

bos.close()

} catch (Exception e) {

Log.info(e.getLocalizedMessage(), e)

}

}

if (fos != null) {

try {

fos.close()

} catch (Exception e) {

Log.info(e.getLocalizedMessage(), e)

}

}

}

}

举例代码：

    /**

     * 下载文件。

     * @param urlStr 文件的URL

     * @param savePath 保存到的目录

     * @param fileName 保存的文件名称

     * @param description 描述（如：歌曲，专辑封面，歌词等）

     * @throws IOException

     */

    public static void downLoad(String urlStr, String savePath, String fileName, String description) throws IOException

    {

        URL url = new URL(urlStr)

        HttpURLConnection conn = (HttpURLConnection) url.openConnection()

        conn.setConnectTimeout(100000)  // 设置超时间为10秒

        conn.setRequestProperty("User-Agent", "Mozilla/4.0 (compatible MSIE 5.0 Windows NT DigExt)")  // 防止屏蔽程序抓取而返回403错误

        File saveDir = new File(savePath)

        File file = new File(saveDir + File.separator + fileName)

        try (InputStream inputStream = conn.getInputStream()

                FileOutputStream fos = new FileOutputStream(file))

        {

            byte[] flowData = readInputStream(inputStream)

            fos.write(flowData)

        } catch (Exception e) {

            MainFrame.logEvent("字节保存时出现意外：" + e.getMessage())

        }

        MainFrame.logEvent(description + "下载完成：" + url)

    }

MainFrame.logEvent()是我自己弄的日志记录而已，可以忽略不看

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