Java通过HttpClient从外部url下载文件到本地

package com.haier.healthroom.kefu.utils;

import org.apache.commons.lang3.StringUtils;
import org.apache.http.*;
import org.apache.http.client.HttpClient;
import org.apache.http.client.methods.HttpGet;
import org.apache.http.impl.client.HttpClients;

import java.io.File;
import java.io.FileOutputStream;
import java.io.InputStream;
import java.util.HashMap;
import java.util.Map;
import java.util.regex.Matcher;
import java.util.regex.Pattern;

/**
 * 一个低端小气没档次的程序狗 JavaDog
 * blog.javadog.net
 *
 * @BelongsProject: healthroom
 * @BelongsPackage: com.haier.healthroom.kefu.utils
 * @Author: hdx
 * @CreateTime: 2021-06-04 10:10
 * @Description: HttpDownload
 */
public class HttpDownloadUtil {

    public static final int cache = 10 * 1024;

    public static void main(String[] args) {
        String url = "https://www.baidu.com/img/flexible/logo/pc/result.png";
        String targetUrl = "E:\\demo\\";
        HttpDownloadUtil.download(url,targetUrl);
    }

    /**
     * 根据url下载文件，保存到filepath中
     *
     * @param url
     * @param diskUrl
     * @return
     */
    public static String download(String url, String diskUrl) {
        String filepath = "";
        String filename = "";
        try {
            HttpClient client = HttpClients.createDefault();
            HttpGet httpget = new HttpGet(url);
            // 加入Referer,防止防盗链
            httpget.setHeader("Referer", url);
            HttpResponse response = client.execute(httpget);
            HttpEntity entity = response.getEntity();
            InputStream is = entity.getContent();
            if (StringUtils.isBlank(filepath)){
                Map<String,String> map = getFilePath(response,url,diskUrl);
                filepath = map.get("filepath");
                filename = map.get("filename");
            }
            File file = new File(filepath);
            file.getParentFile().mkdirs();
            FileOutputStream fileout = new FileOutputStream(file);
            byte[] buffer = new byte[cache];
            int ch = 0;
            while ((ch = is.read(buffer)) != -1) {
                fileout.write(buffer, 0, ch);
            }
            is.close();
            fileout.flush();
            fileout.close();

        } catch (Exception e) {
            e.printStackTrace();
        }
        return filename;
    }

    /**
     * 根据contentType 获取对应的后缀 （列出常用的ContentType对应的后缀）
     *
     * @param contentType
     * @return
     */
    static String getContentType(String contentType){
        HashMap<String, String> map = new HashMap<String, String>() {
            {
                put("application/msword", ".doc");
                put("image/jpeg", ".jpeg");
                put("application/x-jpg", ".jpg");
                put("video/mpeg4", ".mp4");
                put("application/pdf", ".pdf");
                put("application/x-png", ".png");
                put("application/x-ppt", ".ppt");
                put("application/postscript", ".ps");
                put("application/vnd.android.package-archive", ".apk");
                put("video/avi", ".avi");
                put("text/html", ".htm");
                put("image/png", ".png");
                put("application/x-png", ".png");
                put("image/gif", ".gif");
            }
        };
        return map.get(contentType);

    }

    /**
     * 获取response要下载的文件的默认路径
     *
     * @param response
     * @return
     */
    public static Map<String,String> getFilePath(HttpResponse response, String url, String diskUrl) {
        Map<String,String> map = new HashMap<>();
        String filepath = diskUrl;
        String filename = getFileName(response, url);
        String contentType = response.getEntity().getContentType().getValue();
        if(StringUtils.isNotEmpty(contentType)){
            // 获取后缀
            String suffix = getContentType(contentType);
            String regEx = ".+(.+)$";
            Pattern p = Pattern.compile(regEx);
            Matcher m = p.matcher(filename);
            if (!m.find()) {
                // 如果正则匹配后没有后缀，则需要通过response中的ContentType的值进行匹配
                if(StringUtils.isNoneBlank(suffix)){
                    filename = filename + suffix;
                }
            }else{
                if(filename.length()>20){
                    filename = getRandomFileName() + suffix;
                }
            }
        }
        if (filename != null) {
            filepath += filename;
        } else {
            filepath += getRandomFileName();
        }
        map.put("filename", filename);
        map.put("filepath", filepath);
        return map;
    }

    /**
     * 获取response header中Content-Disposition中的filename值
     * @param response
     * @param url
     * @return
     */
    public static String getFileName(HttpResponse response,String url) {
        Header contentHeader = response.getFirstHeader("Content-Disposition");
        String filename = null;
        if (contentHeader != null) {
            // 如果contentHeader存在
            HeaderElement[] values = contentHeader.getElements();
            if (values.length == 1) {
                NameValuePair param = values[0].getParameterByName("filename");
                if (param != null) {
                    try {
                        filename = param.getValue();
                    } catch (Exception e) {
                        e.printStackTrace();
                    }
                }
            }
        }else{
            // 正则匹配后缀
            filename = getSuffix(url);
        }

        return filename;
    }

    /**
     * 获取随机文件名
     *
     * @return
     */
    public static String getRandomFileName() {
        return String.valueOf(System.currentTimeMillis());
    }

    /**
     * 获取文件名后缀
     * @param url
     * @return
     */
    public static String getSuffix(String url) {
        // 正则表达式“.+/(.+)$”的含义就是：被匹配的字符串以任意字符序列开始，后边紧跟着字符“/”，
        // 最后以任意字符序列结尾，“()”代表分组操作，这里就是把文件名做为分组，匹配完毕我们就可以通过Matcher
        // 类的group方法取到我们所定义的分组了。需要注意的这里的分组的索引值是从1开始的，所以取第一个分组的方法是m.group(1)而不是m.group(0)。
        String regEx = ".+/(.+)$";
        Pattern p = Pattern.compile(regEx);
        Matcher m = p.matcher(url);
        if (!m.find()) {
            // 格式错误，则随机生成个文件名
            return String.valueOf(System.currentTimeMillis());
        }
        return m.group(1);

    }
}