java 下载网络文件

1.FileUtils.copyURLToFile实现：

import java.io.File;
import java.net.URL;
import org.apache.commons.io.FileUtils;

public class DownLoadFile {

    /**
     * 网络文件下载保存
     * @param url 文件url
     * @param dir 存储目录
     * @param fileName 存储文件名
     */
    public static void downloadHttpUrl(String url, String dir, String fileName) {
        try {
            URL httpurl = new URL(url);
            File dirfile = new File(dir);
            if (!dirfile.exists()) {
                dirfile.mkdirs();
            }
            FileUtils.copyURLToFile(httpurl, new File(dir+fileName));
        } catch (Exception e) {
            e.printStackTrace();
        }
    } 

    /**
     * 测试
     * @param args
     */
    public static void main(String[] args) {
        downloadHttpUrl("http://gtms03.alicdn.com/tps/i3/TB1VF6uGFXXXXalaXXXmh5R_VXX-237-236.png", "D:/download/", "1.png");
    }
}

图示：

               

2.常规写法：

import java.io.ByteArrayOutputStream;
import java.io.File;
import java.io.FileOutputStream;
import java.io.IOException;
import java.io.InputStream;
import java.net.HttpURLConnection;
import java.net.URL;

public class DownLoadFile {

    /**
     * 从网络Url中下载文件
     *
     * @param urlstr 文件url
     * @param fileName 存储文件名
     * @param savePath 存储路径
     * @throws IOException
     */
    public static String downLoadFromUrl(String urlStr, String fileName, String savePath) {
        try {  

            URL url = new URL(urlStr);
            HttpURLConnection conn = (HttpURLConnection) url.openConnection();
            // 设置超时间为3秒
            conn.setConnectTimeout(3 * 1000);
            // 防止屏蔽程序抓取而返回403错误
            conn.setRequestProperty("User-Agent", "Mozilla/4.0 (compatible; MSIE 5.0; Windows NT; DigExt)");  

            // 得到输入流
            InputStream inputStream = conn.getInputStream();
            // 获取自己数组
            byte[] getData = readInputStream(inputStream);  

            // 文件保存位置
            File saveDir = new File(savePath);
            if (!saveDir.exists()) {
                saveDir.mkdir();
            }
            File file = new File(saveDir + File.separator + fileName);
            FileOutputStream fos = new FileOutputStream(file);
            fos.write(getData);
            if (fos != null) {
                fos.close();
            }
            if (inputStream != null) {
                inputStream.close();
            }
            // System.out.println("info:"+url+" download success");
            return saveDir + File.separator + fileName;
        } catch (Exception e) {
            e.printStackTrace();
        }
        return "";  

    }  

    /**
     * 从输入流中获取字节数组
     *
     * @param inputStream
     * @return
     * @throws IOException
     */
    public static byte[] readInputStream(InputStream inputStream) throws IOException {
        byte[] buffer = new byte[1024];
        int len = 0;
        ByteArrayOutputStream bos = new ByteArrayOutputStream();
        while ((len = inputStream.read(buffer)) != -1) {
            bos.write(buffer, 0, len);
        }
        bos.close();
        return bos.toByteArray();
    }  

    /**
     * 测试
     * @param args
     */
    public static void main(String[] args) {
        downLoadFromUrl("http://gtms03.alicdn.com/tps/i3/TB1VF6uGFXXXXalaXXXmh5R_VXX-237-236.png", "2.png", "D:/download/");
    }

}

图示：