遇到了一个下载文件的问题
在开发中，需要实现一个文件下载的方法，对下载时间有一点要求，对于小文件来说，问题不大，单线程下载既可;
- 单线程下载文件： 首先使用HttpURLConnection获取文件流； 创建RandomAccessFile文件对象，用于写入； 使用 randomAccessFile.write(buffer,0,size);将流转换字节写入文件 另外，可以启动一个单独的线程，记录下载进度； 在HttpURLConnection请求后记录总大小， 在写入文件时记录已下载大小； 使用NumberFormat记录输出百分比；
public boolean downloadFile(String url,String dest_path,int downloadTimeout,boolean downloadResume){
//检测下载进度
new Thread(new Runnable() {
@Override
public void run() {
try {
NumberFormat numberFormat = NumberFormat.getPercentInstance();
numberFormat.setMinimumFractionDigits(2);
logger.debug("是否下载完成：{}",downloadFinish);
while (!downloadFinish){
Thread.sleep(10000);
if(totalSize > 0){
logger.info("已下载大小{},进度：{},如果长时间不更新,可能是进度汇报现场卡了，不影响下载",
getDownloadSize(),
numberFormat.format(getDownloadSize()*1.0/getTotalSize()));
}
}
}catch (Throwable e){
logger.error("记录下载文件进度出错，{}",e.getMessage(),e);
e.printStackTrace();
}
}
}).start();
logger.debug("开始下载,源文件地址：{},n 目标地址：{},n 设置的超时时间为：{}",url,dest_path,downloadTimeout);
try {
RandomAccessFile randomAccessFile = null;
InputStream in = null;
URL fileUrl = new URL(url);
HttpURLConnection connection = (HttpURLConnection)fileUrl.openConnection();
connection.setConnectTimeout(downloadTimeout);
connection.setRequestMethod("GET");
File tempFile = new File(dest_path "_tmp");// 临时文件
if(!tempFile.getParentFile().exists()){
tempFile.getParentFile().mkdirs();
}
if(downloadResume){
if(tempFile.exists() && tempFile.isFile()){
downloadSize = tempFile.length();
startIndex = downloadSize;
}
connection.setRequestProperty("Range", "bytes=" startIndex "-");
}else{
if(tempFile.exists() && tempFile.isFile()){
tempFile.delete();
}
}
int staus = connection.getResponseCode();
totalSize = downloadSize connection.getContentLengthLong();
logger.debug("请求状态码：{},文件总大小：{}[{}],本地需要下载的大小：{}",staus,totalSize, totalSize/1024/1024, totalSize - downloadSize);
if(staus == 200 || staus == 206){
randomAccessFile = new RandomAccessFile(tempFile,"rwd");
randomAccessFile.seek(startIndex);
in = connection.getInputStream();
byte[] buffer = new byte[2048 * 10];
int size = 0;
while ((size = in.read(buffer))!= -1){
randomAccessFile.write(buffer,0,size);
downloadSize = downloadSize size;
}
randomAccessFile.close();
}
in.close();
File dest = new File(dest_path);
this.setDownloadFinish(true);
return tempFile.renameTo(dest);
}catch (Throwable e){
logger.error("下载文件出错，{}",e.getMessage(),e);
}finally {
this.setDownloadFinish(true);
}
return false;
}但对于大文件（超5G）来说，下载时间就会很长，当然这个也需要考虑网络和硬件的关系；但是可以通过多线程的方式下载文件；
- 多线程下载文件:
多线程分片下载文件， 获取文件总大小， 分成指定的份数，再启动指定的线程去下载自己的那一份；
//获取总大小：
private Long getRemoteFileSize(String remoteFileUrl) throws IOException {
代码语言：txt复制 Long fileSize = 0L ; HttpURLConnection httpConnection = (HttpURLConnection) new URL(remoteFileUrl).openConnection(); httpConnection.setRequestMethod("HEAD"); Integer responseCode = 0; try { responseCode = httpConnection.getResponseCode(); } catch (IOException e) { e.printStackTrace(); } if (responseCode >= 400) { System.out.println("Web服务器响应错误!请稍后重试"); return fileSize; } String sHeader; for (Integer i = 1; ; i ) { sHeader = httpConnection.getHeaderFieldKey(i); if ("Content-Length".equals(sHeader)) { fileSize = Long.parseLong(httpConnection.getHeaderField(sHeader)); break; } } return fileSize;}分片：
代码语言：java复制 CountDownLatch countDownLatch = new CountDownLatch(poolLength);
List<FileDownloadRunnable> downloadRunnables = new ArrayList<>();
Long partSize = length / poolLength;
for (int i = 1; i <= poolLength; i ) {
//start = i * length / poolLength;
//long end = (i 1) * length / poolLength - 1;
// 每一个线程下载的开始位置
Long start = (i - 1) * partSize;
// 每一个线程下载的开始位置
Long end = start partSize - 1;
if (i == poolLength) {
//最后一个线程下载的长度稍微长一点
end = length;
}
//System.out.println(start "---------------" end);
FileDownloadRunnable fileDownloadRunnable =
new FileDownloadRunnable(url, dest_path, start, end,countDownLatch);
downloadRunnables.add(fileDownloadRunnable);
Thread thread = new Thread(fileDownloadRunnable);
thread.setName("下载线程" i);
thread.start();
}
countDownLatch.await(); //等待主线程完成
for (FileDownloadRunnable downloadRunnable:downloadRunnables) {
boolean downloadFinish = downloadRunnable.isDownloadFinish();
logger.debug("多个线程是否都下载完成：" downloadRunnable.isDownloadFinish());
if(!downloadFinish){
throw new RuntimeException("链接文件失败，无法落地");
}
}
//FileDownloadRunnable.mergeFiles(dest_path,poolLength,false);
long endTime = System.currentTimeMillis();
logger.debug("文件下载完成，总耗时：{}s",(endTime - startTime) / 1000);
return true;下载：
代码语言：java复制public class FileDownloadRunnable implements Runnable{
//下载路径
private String urlLocation;
//下载完存放路径
private String filePath;
//文件开始地址
public Long start;
//文件结束地址
public Long end;
private CountDownLatch countDownLatch;
ThreadLocal<Long> startTime = new ThreadLocal<>();
NumberFormat numberFormat = NumberFormat.getPercentInstance();
Long allSize = 1L;
private boolean downloadFinish = false;
public FileDownloadRunnable(String urlLocation, String filePath, Long start, Long end, CountDownLatch countDownLatch) {
this.urlLocation = urlLocation;
this.filePath = filePath;
this.start = start;
this.end = end;
this.countDownLatch = countDownLatch;
numberFormat.setMinimumFractionDigits(2);
allSize = end-start;
}
@Override
public void run() {
InputStream is = null;
//FileOutputStream out = null;
RandomAccessFile out = null;
try {
File file = new File(filePath);
if(!file.getParentFile().exists()){
file.getParentFile().mkdirs();
}
startTime.set(System.currentTimeMillis());
System.out.println(start "-" end);
//获取下载的部分
URL url = new URL(urlLocation);
HttpURLConnection conn = (HttpURLConnection) url.openConnection();
conn.setReadTimeout(6000);
conn.setRequestMethod("GET");
conn.setRequestProperty("Range", "bytes=" start "-" end);
conn.setRequestProperty("Connection", "Keep-Alive");
//conn.setRequestProperty("User-Agent","Mozilla/5.0 (Windows NT 6.1; WOW64) AppleWebKit/535.1 (KHTML, like Gecko) Chrome/14.0.835.163 Safari/535.1");
//conn.connect();
int statusCode = conn.getResponseCode();
long length = conn.getContentLengthLong();
System.out.println(Thread.currentThread().getName() "：请求状态码：" statusCode "，请求到的大小:" length "=" length/1024/1024 "M");
is = conn.getInputStream();
//System.out.println("getInputStream().available():" is.available());
//BufferedInputStream bis = new BufferedInputStream(is);
//out = new FileOutputStream(filePath);
out = new RandomAccessFile(file, "rw");
out.seek(start);
//System.out.println("out.seek:" start);
byte[] bytes = new byte[2048 * 10];
int l = 0;
//int totalSize = 0;
while ((l = is.read(bytes))!=-1){
//totalSize = l;
out.write(bytes,0,l);
}
//bis.close();
out.close();
is.close();
long time = System.currentTimeMillis() - startTime.get();
downloadFinish = true; //下载完成标识
System.out.println(Thread.currentThread().getName() "完成下载！共耗时(秒):" time/1000);
} catch (Throwable e) {
e.printStackTrace();
throw new RuntimeException(Thread.currentThread().getName() "下载失败",e);
} finally {
countDownLatch.countDown();
}
}
public boolean isDownloadFinish() {
return downloadFinish;
}未解决的问题：
下载时遇到一个问题，挂载盘和本地盘下载结果不一致；不知道是不是挂载盘方式的问题？
