下载一个文件需要你阅读它。无论哪种方式，您都必须以某种方式查看该文件。而不是逐行，你可以从流中逐字节读取:

BufferedInputStream in = new BufferedInputStream(new URL("http://www.website.com/information.asp").openStream())
byte data[] = new byte[1024];
int count;
while((count = in.read(data, 0, 1024)) != -1)
{
    out.write(data, 0, count);
}

简单使用有一个问题:

org.apache.commons.io.FileUtils.copyURLToFile(URL, File)

如果你需要下载和保存非常大的文件，或者在一般情况下，如果你需要自动重试以防连接断开。

在这种情况下，我建议使用Apache HttpClient以及org.apache.commons.io.FileUtils。例如:

GetMethod method = new GetMethod(resource_url);
try {
    int statusCode = client.executeMethod(method);
    if (statusCode != HttpStatus.SC_OK) {
        logger.error("Get method failed: " + method.getStatusLine());
    }
    org.apache.commons.io.FileUtils.copyInputStreamToFile(
        method.getResponseBodyAsStream(), new File(resource_file));
    } catch (HttpException e) {
        e.printStackTrace();
    } catch (IOException e) {
        e.printStackTrace();
    } finally {
    method.releaseConnection();
}

这个答案几乎和选中的答案完全一样，但是有两个增强:它是一个方法，它关闭了FileOutputStream对象:

    public static void downloadFileFromURL(String urlString, File destination) {
        try {
            URL website = new URL(urlString);
            ReadableByteChannel rbc;
            rbc = Channels.newChannel(website.openStream());
            FileOutputStream fos = new FileOutputStream(destination);
            fos.getChannel().transferFrom(rbc, 0, Long.MAX_VALUE);
            fos.close();
            rbc.close();
        } catch (IOException e) {
            e.printStackTrace();
        }
    }

更简单的非阻塞I/O用法:

URL website = new URL("http://www.website.com/information.asp");
try (InputStream in = website.openStream()) {
    Files.copy(in, target, StandardCopyOption.REPLACE_EXISTING);
}

在underscore-java库中有一个方法U.fetch(url)。

文件pom.xml:

<dependency>
  <groupId>com.github.javadev</groupId>
  <artifactId>underscore</artifactId>
  <version>1.84</version>
</dependency>

代码示例:

import com.github.underscore.U;
import java.io.IOException;
import java.nio.file.Files;
import java.nio.file.Paths;

public class Download {
    public static void main(String[] args) throws IOException {
        Files.write(Paths.get("data.bin"),
            U.fetch("https://stackoverflow.com/questions"
                + "/921262/how-to-download-and-save-a-file-from-internet-using-java").blob());
    }
}

下面是一个简洁的、可读的、仅使用jdk的解决方案，其中包含适当的封闭资源:

static long download(String url, String fileName) throws IOException {
    try (InputStream in = URI.create(url).toURL().openStream()) {
        return Files.copy(in, Paths.get(fileName));
    }
}

两行代码，没有依赖关系。

下面是一个完整的文件下载示例程序，包含输出、错误检查和命令行参数检查:

package so.downloader;

import java.io.IOException;
import java.io.InputStream;
import java.net.URI;
import java.nio.file.Files;
import java.nio.file.Paths;

public class Application {
    public static void main(String[] args) throws IOException {
        if (2 != args.length) {
            System.out.println("USAGE: java -jar so-downloader.jar <source-URL> <target-filename>");
            System.exit(1);
        }

        String sourceUrl = args[0];
        String targetFilename = args[1];

        long bytesDownloaded = download(sourceUrl, targetFilename);

        System.out.println(String.format("Downloaded %d bytes from %s to %s.", bytesDownloaded, sourceUrl, targetFilename));
    }

    static long download(String url, String fileName) throws IOException {
        try (InputStream in = URI.create(url).toURL().openStream()) {
            return Files.copy(in, Paths.get(fileName));
        }
    }    
}

正如so-downloader存储库README中所指出的:

运行文件下载程序:

java -jar so-downloader.jar <source-URL> <target-filename>

例如:

java -jar so-downloader.jar https://github.com/JanStureNielsen/so-downloader/archive/main.zip so-downloader-source.zip