HttpClient实现通过url下载文件

其实就是通过浏览器url，点击就会下载文件。

这里是从代码层面上，对文件进行下载。

package main.java.com.abp.util;

import org.apache.http.*;
import org.apache.http.client.HttpClient;
import org.apache.http.client.methods.HttpGet;
import org.apache.http.impl.client.DefaultHttpClient;
import org.apache.http.impl.client.HttpClients;

import java.io.File;
import java.io.FileOutputStream;
import java.io.InputStream;

public class HttpDownload {
    public static final int cache = 10 * 1024;
    public static final boolean isWindows;
    public static final String splash;
    public static final String root;

    static {
        if (System.getProperty("os.name") != null && System.getProperty("os.name").toLowerCase().contains("windows")) {
            isWindows = true;
            splash = "\\";
            root = "D:";
        } else {
            isWindows = false;
            splash = "/";
            root = "/search";
        }
    }

    /**
     * 根据url下载文件，文件名从response header头中获取
     *
     * @param url
     * @return
     */
    public static String download(String url) {
        return download(url, null);
    }

    /**
     * 根据url下载文件，保存到filepath中
     *
     * @param url
     * @param filepath
     * @return
     */
    public static String download(String url, String filepath) {
        try {
            HttpClient client = HttpClients.createDefault();
            HttpGet httpget = new HttpGet(url);
            HttpResponse response = client.execute(httpget);

            HttpEntity entity = response.getEntity();
            InputStream is = entity.getContent();
            if (filepath == null){
                filepath = getFilePath(response);
            }

            File file = new File(filepath);
            file.getParentFile().mkdirs();
            FileOutputStream fileout = new FileOutputStream(file);
            /**
             * 根据实际运行效果 设置缓冲区大小
             */
            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 null;
    }

    /**
     * 获取response要下载的文件的默认路径
     *
     * @param response
     * @return
     */
    public static String getFilePath(HttpResponse response) {
        String filepath = root + splash;
        String filename = getFileName(response);

        if (filename != null) {
            filepath += filename;
        } else {
            filepath += getRandomFileName();
        }
        return filepath;
    }

    /**
     * 获取response header中Content-Disposition中的filename值
     *
     * @param response
     * @return
     */
    public static String getFileName(HttpResponse response) {
        Header contentHeader = response.getFirstHeader("Content-Disposition");
        String filename = null;
        if (contentHeader != null) {
            HeaderElement[] values = contentHeader.getElements();
            if (values.length == 1) {
                NameValuePair param = values[0].getParameterByName("filename");
                if (param != null) {
                    try {
                        //filename = new String(param.getValue().toString().getBytes(), "utf-8");
                        //filename=URLDecoder.decode(param.getValue(),"utf-8");
                        filename = param.getValue();
                    } catch (Exception e) {
                        e.printStackTrace();
                    }
                }
            }
        }
        return filename;
    }

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

    public static void outHeaders(HttpResponse response) {
        Header[] headers = response.getAllHeaders();
        for (int i = 0; i < headers.length; i++) {
            System.out.println(headers[i]);
        }
    }

    public static void main(String[] args) {
        String url = "https://codeload.github.com/douban/douban-client/legacy.zip/master";
        String filepath = "F:\\xxxx\\workspace\\httpClientProj\\file\\test.zip";
        HttpDownload.download(url, filepath);
    }
}

测试（可忽略，主要自己业务要用到）

@Test
    public void test1(){
        String docRootPath =  "F:\\xxxx\\workspace\\httpClientProj\\file";
        String readFileName = "test.zip";
        String writeFileName = "write.zip";

        File readFile = new File(docRootPath+"\\"+readFileName);
        File writeFile = new File(docRootPath+"\\"+writeFileName);

        try {
            byte[] content1 = "CONTENT=".getBytes();
            byte[] content2 = FileUtils.readFileToByteArray(readFile);

            //拷贝文件文件
            FileUtils.writeByteArrayToFile(writeFile,content1);
            FileUtils.writeByteArrayToFile(writeFile,content2,true);
            System.out.println("------------------------------ok");

        } catch (IOException e) {
            e.printStackTrace();
        }
    }

    @Test
    public void test2(){
        String docRootPath =  "F:\\xxxx\\workspace\\httpClientProj\\file";
        String readFileName = "write.zip";
        String writeFileName = "write1.zip";

        File readFile = new File(docRootPath+"\\"+readFileName);
        File writeFile = new File(docRootPath+"\\"+writeFileName);

        try {
            byte[] content1 = "CONTENT=".getBytes();
            int startIndex = content1.length;

            byte[] content2 = FileUtils.readFileToByteArray(readFile);

            byte[] content3 = Arrays.copyOfRange(content2,startIndex,content2.length);

            //拷贝文件文件
            FileUtils.writeByteArrayToFile(writeFile,content3);
            System.out.println("------------------------------ok");

        } catch (IOException e) {
            e.printStackTrace();
        }
    }