Java如何从服务器下载文件到本地？-凌峰创科服务平台

Java 从服务器下载文件到本地

在 Java 中，有几种常见的方法可以从服务器下载文件到本地，以下是几种实现方式：

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使用 Java 原生 HTTPURLConnection

import java.io.*;
import java.net.HttpURLConnection;
import java.net.URL;
public class FileDownloader {
    public static void downloadFile(String fileUrl, String savePath) throws IOException {
        URL url = new URL(fileUrl);
        HttpURLConnection connection = (HttpURLConnection) url.openConnection();
        connection.setRequestMethod("GET");
        try (InputStream in = connection.getInputStream();
             FileOutputStream out = new FileOutputStream(savePath)) {
            byte[] buffer = new byte[1024];
            int bytesRead;
            while ((bytesRead = in.read(buffer)) != -1) {
                out.write(buffer, 0, bytesRead);
            }
        }
        connection.disconnect();
    }
    public static void main(String[] args) {
        String fileUrl = "http://example.com/path/to/file.zip";
        String savePath = "C:/downloads/file.zip";
        try {
            downloadFile(fileUrl, savePath);
            System.out.println("文件下载成功: " + savePath);
        } catch (IOException e) {
            System.err.println("文件下载失败: " + e.getMessage());
        }
    }
}

使用 Apache HttpClient (更强大和灵活)

首先添加依赖：

<dependency>
    <groupId>org.apache.httpcomponents</groupId>
    <artifactId>httpclient</artifactId>
    <version>4.5.13</version>
</dependency>

然后使用以下代码：

import org.apache.http.HttpEntity;
import org.apache.http.client.methods.CloseableHttpResponse;
import org.apache.http.client.methods.HttpGet;
import org.apache.http.impl.client.CloseableHttpClient;
import org.apache.http.impl.client.HttpClients;
import java.io.*;
public class HttpClientDownloader {
    public static void downloadFile(String fileUrl, String savePath) throws IOException {
        try (CloseableHttpClient httpClient = HttpClients.createDefault();
             CloseableHttpResponse response = httpClient.execute(new HttpGet(fileUrl))) {
            HttpEntity entity = response.getEntity();
            if (entity != null) {
                try (InputStream in = entity.getContent();
                     FileOutputStream out = new FileOutputStream(savePath)) {
                    byte[] buffer = new byte[1024];
                    int bytesRead;
                    while ((bytesRead = in.read(buffer)) != -1) {
                        out.write(buffer, 0, bytesRead);
                    }
                }
            }
        }
    }
    public static void main(String[] args) {
        String fileUrl = "http://example.com/path/to/file.zip";
        String savePath = "C:/downloads/file.zip";
        try {
            downloadFile(fileUrl, savePath);
            System.out.println("文件下载成功: " + savePath);
        } catch (IOException e) {
            System.err.println("文件下载失败: " + e.getMessage());
        }
    }
}

使用 Java NIO (适用于大文件)

import java.io.*;
import java.net.URI;
import java.net.http.HttpClient;
import java.net.http.HttpRequest;
import java.net.http.HttpResponse;
import java.nio.file.Files;
import java.nio.file.Path;
import java.nio.file.Paths;
public class NioDownloader {
    public static void downloadFile(String fileUrl, String savePath) throws IOException, InterruptedException {
        HttpClient client = HttpClient.newBuilder()
                .followRedirects(HttpClient.Redirect.ALWAYS)
                .build();
        HttpRequest request = HttpRequest.newBuilder()
                .uri(URI.create(fileUrl))
                .build();
        HttpResponse<InputStream> response = client.send(request, 
                HttpResponse.BodyHandlers.ofInputStream());
        Path destination = Paths.get(savePath);
        Files.copy(response.body(), destination);
    }
    public static void main(String[] args) {
        String fileUrl = "http://example.com/path/to/file.zip";
        String savePath = "C:/downloads/file.zip";
        try {
            downloadFile(fileUrl, savePath);
            System.out.println("文件下载成功: " + savePath);
        } catch (IOException | InterruptedException e) {
            System.err.println("文件下载失败: " + e.getMessage());
        }
    }
}

带进度显示的下载

import java.io.*;
import java.net.URL;
import java.net.URLConnection;
public class ProgressDownloader {
    public static void downloadFile(String fileUrl, String savePath) throws IOException {
        URL url = new URL(fileUrl);
        URLConnection connection = url.openConnection();
        int fileSize = connection.getContentLength();
        try (InputStream in = connection.getInputStream();
             FileOutputStream out = new FileOutputStream(savePath)) {
            byte[] buffer = new byte[1024];
            int bytesRead;
            long totalBytesRead = 0;
            while ((bytesRead = in.read(buffer)) != -1) {
                out.write(buffer, 0, bytesRead);
                totalBytesRead += bytesRead;
                int progress = (int) (totalBytesRead * 100 / fileSize);
                System.out.printf("下载进度: %d%%\n", progress);
            }
        }
    }
    public static void main(String[] args) {
        String fileUrl = "http://example.com/path/to/file.zip";
        String savePath = "C:/downloads/file.zip";
        try {
            downloadFile(fileUrl, savePath);
            System.out.println("文件下载成功: " + savePath);
        } catch (IOException e) {
            System.err.println("文件下载失败: " + e.getMessage());
        }
    }
}