Java下http下载文件客户端和上传文件客户端实例代码

让我为您详细讲解Java下http下载文件客户端和上传文件客户端实例代码的完整攻略。

一、http下载文件客户端代码示例

1.1 通过Java SE自带库实现

使用Java SE自带库实现简单的http下载文件客户端代码，只需要用到Java SE自带的URL和HttpURLConnection两个类即可。

import java.io.BufferedInputStream;
import java.io.BufferedOutputStream;
import java.io.FileOutputStream;
import java.io.IOException;
import java.net.HttpURLConnection;
import java.net.URL;

public class HttpDownloadClient {
    public static void downloadFile(String downloadUrl, String savePath) throws IOException {
        URL url = new URL(downloadUrl);
        HttpURLConnection conn = (HttpURLConnection) url.openConnection();
        conn.setConnectTimeout(5000); // 设置连接超时时间为5秒
        conn.setRequestMethod("GET"); // 设置请求方法为GET
        BufferedInputStream bis = new BufferedInputStream(conn.getInputStream());
        BufferedOutputStream bos = new BufferedOutputStream(new FileOutputStream(savePath));
        byte[] buffer = new byte[1024];
        int len;
        while ((len = bis.read(buffer)) != -1) {
            bos.write(buffer, 0, len);
        }
        bis.close();
        bos.close();
        conn.disconnect();
    }
}

在使用该代码的时候，只需要调用downloadFile方法，传入文件下载链接和保存路径即可。比如下载百度的logo，保存在本地的D:/filename.png，示例如下：

public static void main(String[] args) {
    try {
        String downloadUrl = "http://www.baidu.com/img/bd_logo1.png";
        String savePath = "D:/filename.png";
        HttpDownloadClient.downloadFile(downloadUrl, savePath);
        System.out.println("Download successed!");
    } catch (IOException e) {
        e.printStackTrace();
    }
}

1.2 使用Apache的HttpClient库实现

由于Java自带的库比较简单，一些高级的操作都没有提供接口或者比较薄弱，因此，Apache曾经开发了一个类库——HttpClient，该类库提供了很多比Java SE自带库强的特性，如连接池、多线程、身份验证、重定向、Cookie自动管理等。使用HttpClient下载文件非常简单，只需调用实例中的execute方法即可。

import java.io.FileOutputStream;
import java.io.IOException;
import java.io.InputStream;
import java.net.URL;

import org.apache.http.HttpEntity;
import org.apache.http.HttpResponse;
import org.apache.http.client.methods.HttpGet;
import org.apache.http.client.utils.URIBuilder;
import org.apache.http.impl.client.CloseableHttpClient;
import org.apache.http.impl.client.HttpClients;
import org.apache.http.util.EntityUtils;

public class HttpDownloadClient {
    public static void downloadFile(String downloadUrl, String savePath) throws Exception {
        CloseableHttpClient httpClient = HttpClients.createDefault();
        URIBuilder uriBuilder = new URIBuilder(downloadUrl);
        HttpGet httpGet = new HttpGet(uriBuilder.build());
        HttpResponse response = httpClient.execute(httpGet);
        HttpEntity entity = response.getEntity();
        InputStream inputStream = entity.getContent();
        FileOutputStream fileOutputStream = new FileOutputStream(savePath);
        byte[] buffer = new byte[1024];
        int len;
        while ((len = inputStream.read(buffer)) != -1) {
            fileOutputStream.write(buffer, 0, len);
        }
        fileOutputStream.close();
        inputStream.close();
        EntityUtils.consume(entity);
        httpClient.close();
    }
}

下载方法的使用方式和之前的Java SE自带库示例是一致的，只需调用downloadFile方法传入文件下载链接和保存路径即可。

二、http上传文件客户端代码示例

2.1 使用Java SE自带库实现

使用Java SE自带库实现简单的http上传文件客户端代码，同样只需要用到Java SE自带的URL和HttpURLConnection两个类即可。

import java.io.File;
import java.io.FileInputStream;
import java.io.IOException;
import java.io.OutputStream;
import java.net.HttpURLConnection;
import java.net.URL;

public class HttpUploadClient {
    public static void uploadFile(String uploadUrl, String filePath) throws IOException {
        File file = new File(filePath);
        HttpURLConnection conn = (HttpURLConnection) new URL(uploadUrl).openConnection();
        conn.setDoOutput(true); // 设置为POST请求
        conn.setRequestMethod("POST"); // 设置请求方法为POST
        OutputStream os = conn.getOutputStream();
        FileInputStream fis = new FileInputStream(file);
        byte[] buffer = new byte[1024];
        int len;
        while ((len = fis.read(buffer)) != -1) {
            os.write(buffer, 0, len);
        }
        fis.close();
        os.close();
        int respCode = conn.getResponseCode(); // 获取响应码
        if (respCode == HttpURLConnection.HTTP_OK) {
            System.out.println("Upload successed!");
        } else {
            System.out.println("Upload failed:" + respCode);
        }
    }
}

在使用该代码的时候，只需要调用uploadFile方法，传入文件上传链接和要上传的文件路径即可。比如上传本地的D:/test.txt文件到一个叫做upload的服务器：

public static void main(String[] args) {
    try {
        String uploadUrl = "http://upload.com/api/upload";
        String filePath = "D:/test.txt";
        HttpUploadClient.uploadFile(uploadUrl, filePath);
    } catch (IOException e) {
        e.printStackTrace();
    }
}

2.2 使用Apache的HttpClient库实现

使用HttpClient库实现上传文件同样很简单，只需构造HttpPost对象，然后设置上传的文件，再调用实例中的execute方法即可。

import java.io.File;
import java.io.IOException;

import org.apache.http.HttpEntity;
import org.apache.http.HttpResponse;
import org.apache.http.client.methods.HttpPost;
import org.apache.http.entity.ContentType;
import org.apache.http.entity.mime.MultipartEntityBuilder;
import org.apache.http.entity.mime.content.FileBody;
import org.apache.http.impl.client.CloseableHttpClient;
import org.apache.http.impl.client.HttpClients;
import org.apache.http.util.EntityUtils;

public class HttpUploadClient {
    public static void uploadFile(String uploadUrl, String filePath) throws Exception {
        CloseableHttpClient httpClient = HttpClients.createDefault();
        HttpPost httpPost = new HttpPost(uploadUrl);
        MultipartEntityBuilder builder = MultipartEntityBuilder.create();
        builder.addPart("file", new FileBody(new File(filePath), ContentType.DEFAULT_BINARY));
        HttpEntity httpEntity = builder.build();
        httpPost.setEntity(httpEntity);
        HttpResponse response = httpClient.execute(httpPost);
        HttpEntity entity = response.getEntity();
        String responseMsg = EntityUtils.toString(entity, "UTF-8");
        EntityUtils.consume(entity);
        httpClient.close();        

        int respCode = response.getStatusLine().getStatusCode(); // 获取响应码
        if (respCode == HttpURLConnection.HTTP_OK) {
            System.out.println("Upload successed!");
            System.out.println("Response message: " + responseMsg);
        } else {
            System.out.println("Upload failed:" + respCode);
        }
    }
}

上传方法的使用方式和之前的Java SE自带库示例是一致的，只需调用uploadFile方法传入文件上传链接和要上传的文件路径即可。

以上就是Java下http下载文件客户端和上传文件客户端的完整攻略，希望能对您有所帮助。