断点下载文件Java代码，断点下载文件java,使用标准的JDK方法编写

断点下载文件Java代码，断点下载文件java,使用标准的JDK方法编写

使用标准的JDK方法编写的下载，不含其它开源控件。```javapackage common.http.down;

import java.io.FileNotFoundException;import java.io.IOException;import java.io.InputStream;import java.io.RandomAccessFile;import java.net.HttpURLConnection;import java.net.MalformedURLException;import java.net.URL;import java.util.Iterator;import java.util.List;import java.util.Map;

import org.apache.commons.logging.Log;import org.apache.commons.logging.LogFactory;

public class DownFile {

private static final Log log = LogFactory.getLog(DownFile.class);private static boolean running; // 是否运行中,避免线程不能释放private static Long fileLength = 0L;//文件的大小private static Long bytesum = 0L;//已获取的文件大小private static Long ssll = 0L;//当前传输流量private static long beginTime;//开始下载时间public DownFile() {}public static Long getFileSize(URL url) throws IOException{    //获取一些参数    HttpURLConnection checkurlconn = getHttpConnection(url,0);    String contentLength = checkurlconn.getHeaderField("Content-Length");    checkurlconn.disconnect();    if (contentLength != null) {        try {            return Long.parseLong(contentLength);        } catch (Exception e) {        }    }    return 0L;}public static String getFileName(String urlpath){    String filename = urlpath.substring(urlpath.lastIndexOf("/")+1);    if(filename.indexOf("?")>=0){        filename = filename.substring(0, filename.indexOf("?"));    }    return filename;}public static void downloadNet() throws IOException {    // 下载网络文件    int byteread = 0;    beginTime = System.currentTimeMillis();    MonitorThread monitorThread = new MonitorThread();    String urlpath = "http://dldir1.qq.com/qqfile/qq/QQ7.3/15034/QQ7.3.exe";    //urlpath = "http://archive.apache.org/dist/tomcat/tomcat-8/v8.0.9/bin/apache-tomcat-8.0.9-windows-x64.zip";    URL url = new URL(urlpath);    fileLength =getFileSize(url);    String filename = getFileName(urlpath);    RandomAccessFile destFile = new RandomAccessFile("c:/"+filename, "rw");    bytesum =destFile.length();     if(bytesum>0&amp;&amp;bytesum.equals(fileLength)){        destFile.close();        throw new IOException("文件已被下载完成！");    }    HttpURLConnection httpUrlConnection = getHttpConnection(url,bytesum);    if(httpUrlConnection.getHeaderField("Content-Range")==null){        log.info("当前网站不支持续传");        destFile.seek(0);        bytesum=0L;    }    if(bytesum>0){//文件已存在，判断是否需要下载        log.info(filename+"已下载了"+getFileSize(bytesum)+"继续下载！");        destFile.seek(bytesum);    }    try {        running = true;        monitorThread.start();        InputStream inStream = httpUrlConnection.getInputStream();        byte[] buffer = new byte[1204];        while ((byteread = inStream.read(buffer)) != -1) {            bytesum += byteread;            ssll += byteread;            destFile.write(buffer, 0, byteread);        }        running = false;    } catch (FileNotFoundException e) {        e.printStackTrace();    } catch (IOException e) {        e.printStackTrace();    }finally{        destFile.close();    }}private static HttpURLConnection getHttpConnection(URL url,long pos)        throws IOException {    // 默认的会处理302请求    HttpURLConnection.setFollowRedirects(false);    HttpURLConnection httpConnection = null;    httpConnection = (HttpURLConnection) url.openConnection();    httpConnection.setRequestProperty("RANGE", "bytes=" + pos + "-");    int responseCode = httpConnection.getResponseCode();    log.debug("服务器返回:" + responseCode);    Map<String, List<String>> headers = httpConnection.getHeaderFields();    Iterator<String> iterator = headers.keySet().iterator();    while (iterator.hasNext()) {        String key = iterator.next();        String value = "";        for (String v : headers.get(key)) {            value = ";" + v;        }        log.debug(key + "=" + value);    }    if (responseCode < 200 || responseCode >= 400) {        throw new IOException("服务器返回无效信息:" + responseCode);    }    return httpConnection;}public static void main(String[] args) {    try {        downloadNet();    } catch (MalformedURLException e) {        e.printStackTrace();    } catch (IOException e) {        e.printStackTrace();    }}private static class MonitorThread extends Thread {    public void run() {        try {            while (running) {                log.info(getDesc());//打印进度                ssll = 0L;                sleep(1000);            }        } catch (Exception e) {            e.printStackTrace();            log.error(e);        } finally {        }    }}private static String getDesc() {    return String.format("已下载/总大小=%s/%s(%s),速度:%s,耗时:%s,剩余大小:%s,大约需要:%s",            getFileSize(bytesum),            getFileSize(fileLength),            getProgress(fileLength, bytesum),            getFileSize(ssll),            getTime((System.currentTimeMillis() - beginTime) / 1000),            getFileSize(fileLength - bytesum),            (ssll==0?"未知":getTime((fileLength - bytesum) / ssll)));}private static String getFileSize(long totals) {    // 计算文件大小    int i = 0;    String j = "BKMGT";    float s = totals;    while (s > 1024) {        s /= 1024;        i++;    }    return String.format("%.2f", s) + j.charAt(i);}private static String getProgress(long totals, long read) {    if (totals == 0)        return "0%";    return String.format("%d", read * 100 / totals) + "%";}private static String getTime(long seconds) {    int i = 0;    String j = "秒分时天";    long s = seconds;    String result = "";    while (s > 0) {        if (s % 60 > 0) {            result = String.valueOf(s % 60) + (char) j.charAt(i) + result;        }        s /= 60;        i++;    }    return result;}

}```