ASPIRE

如何用Java下载binary文件

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缘由：

本文主要是对之前记录的「Java中如何发起HTTP请求」一文的补充/修正，当时只考虑了用Java发起GET/POST请求，然后读取返回的文本格式的response信息，在下载文本格式的文件时没啥问题，但是对于binary等非文本格式的文件时就有问题了，这里记录一下解决办法以及产生这个问题的原因，方便以后参考。

正文：

参考解答：

当你想下载一个二进制文件时，不要将 InputStream 嵌入任何的 Reader 类型变量中，而应该是 stream 格式读入，（可以借助于一个字节数组作为缓冲区）然后 stream 格式写出。

如果你在这中间使用了任何类型的 Reader 变量，将内容先转换成了 字符/字符串 再写出至文件，（大概率）就会受到平台编码方式的影响，最后的结果可能就和你预期的不一致了。

If you are trying to read a binary stream, you should NOT wrap the InputStream in a Reader of any kind.Read the data into a byte array buffer using the InputStream.read(byte[], int, int) method. Then write from the buffer to a FileOutputStream.

使用 HttpClient 和 FileUtils.copyInputStreamToFile 以及 FileOutputStream 的方式：

package com.ixyzero.learn.utils;

import org.apache.commons.io.FileUtils;
import org.apache.http.HttpResponse;
import org.apache.http.client.HttpClient;
import org.apache.http.client.methods.HttpGet;
import org.apache.http.impl.client.HttpClientBuilder;

import java.io.*;
import java.net.HttpURLConnection;
import java.net.MalformedURLException;
import java.net.ProtocolException;
import java.net.URL;

/**
 * Created by ixyzero on 2019/9/14.
 */
public class DownloadBinaryFile {

    // HttpURLConnection download from remote url to local file
    public static void httpGetBinary2(String url, File file) {
        URL obj = null;
        HttpURLConnection con = null;
        try {
            obj = new URL(url);
            con = (HttpURLConnection) obj.openConnection();

            con.setRequestMethod("GET");
            con.setRequestProperty("User-Agent", "Mozilla/5.0");

            int responseCode = con.getResponseCode();
            System.out.println("\nSending 'GET' request to URL : " + url);
            System.out.println("Response Code : " + responseCode);

            InputStream inputStream = con.getInputStream();
            byte[] buffer = new byte[4096];
            int n;

            OutputStream output = new FileOutputStream( file );
            while ((n = inputStream.read(buffer)) != -1) {
                output.write(buffer, 0, n);
            }
            output.close();

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

    }

    // HttpClient download from remote url to local file
    public static void httpGetBinary(String url, File file) {
        HttpClient client = HttpClientBuilder.create().build();
        // code below adds HTTP REDIRECT support to GET and POST methods
        // HttpClient client = HttpClientBuilder.create().setRedirectStrategy(new LaxRedirectStrategy()).build();

        HttpGet request = new HttpGet(url);
        request.addHeader("User-Agent", "Mozilla/5.0");

        try {
            HttpResponse response = client.execute(request);
            System.out.println("Response Code : " + response.getStatusLine().getStatusCode());

            InputStream inputStream = response.getEntity().getContent();

            FileUtils.copyInputStreamToFile(inputStream, file);
        } catch (IOException e) {
            e.printStackTrace();
        } finally {
            //
        }

    }

    public static void main(String[] args) {
        DownloadBinaryFile downloader = new DownloadBinaryFile();
        String url1 = "https://www.cnblogs.com/images/logo_small.gif";
        String filepath1 = "/path/to/logo.gif";
        String filepath2 = "/path/to/logo2.gif";

        downloader.httpGetBinary(url1, new File(filepath1));
        downloader.httpGetBinary2(url1, new File(filepath2));
    }
}
参考链接：

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