以下是一个简单的Java程序，用于爬取网站上的图片并下载到本地文件夹：

import java.io.*;
import java.net.*;public class ImageSpider {public static void main(String[] args) {// 确定要爬取的网站URL和本地保存目录String url = "https://www.example.com";String saveDir = "D:/images/";// 读取网页HTML源代码String html = getHtml(url);// 提取其中的图片URLString[] imgUrls = extractImgUrls(html);// 下载图片到本地for (String imgUrl : imgUrls) {downloadImage(imgUrl, saveDir);}}// 读取网页HTML源代码public static String getHtml(String url) {StringBuilder html = new StringBuilder();try {URLConnection conn = new URL(url).openConnection();BufferedReader reader = new BufferedReader(new InputStreamReader(conn.getInputStream()));String line;while ((line = reader.readLine()) != null) {html.append(line);}reader.close();} catch (IOException e) {e.printStackTrace();}return html.toString();}// 提取图片URLpublic static String[] extractImgUrls(String html) {String[] imgUrls = html.split("<img");String[] result = new String[imgUrls.length - 1];for (int i = 1; i < imgUrls.length; i++) {String imgUrl = imgUrls[i].substring(imgUrls[i].indexOf("src=") + 5);imgUrl = imgUrl.substring(0, imgUrl.indexOf("\""));result[i - 1] = imgUrl;}return result;}// 下载图片到本地public static void downloadImage(String imgUrl, String saveDir) {try {URL url = new URL(imgUrl);HttpURLConnection conn = (HttpURLConnection) url.openConnection();conn.setRequestMethod("GET");conn.setConnectTimeout(5 * 1000);InputStream inStream = conn.getInputStream();byte[] data = readInputStream(inStream);File file = new File(saveDir + imgUrl.substring(imgUrl.lastIndexOf("/") + 1));FileOutputStream outStream = new FileOutputStream(file);outStream.write(data);outStream.close();} catch (IOException e) {e.printStackTrace();}}// 读取输入流并转换为字节数组public static byte[] readInputStream(InputStream inputStream) throws IOException {ByteArrayOutputStream outputStream = new ByteArrayOutputStream();byte[] buffer = new byte[1024];int len;while ((len = inputStream.read(buffer)) != -1) {outputStream.write(buffer, 0, len);}inputStream.close();return outputStream.toByteArray();}
}

这个程序首先读取指定网址的HTML源码，然后从中提取出所有的图片URL。最后，程序利用 Java 的 IO 功能下载这些图片并保存到指定的本地文件夹中。

需要注意的是，该程序只是一个简单的演示，实际使用时需要注意合法性和合理性问题，比如设置超时时间、判断文件是否存在等。此外，爬虫在爬取网站时需要遵守网站的爬取协议和法律法规，不能侵犯他人的权益。以下是一个简单的Java程序，用于爬取网站上的图片并下载到本地文件夹：

import java.io.*;
import java.net.*;public class ImageSpider {public static void main(String[] args) {// 确定要爬取的网站URL和本地保存目录String url = "https://www.example.com";String saveDir = "D:/images/";// 读取网页HTML源代码String html = getHtml(url);// 提取其中的图片URLString[] imgUrls = extractImgUrls(html);// 下载图片到本地for (String imgUrl : imgUrls) {downloadImage(imgUrl, saveDir);}}// 读取网页HTML源代码public static String getHtml(String url) {StringBuilder html = new StringBuilder();try {URLConnection conn = new URL(url).openConnection();BufferedReader reader = new BufferedReader(new InputStreamReader(conn.getInputStream()));String line;while ((line = reader.readLine()) != null) {html.append(line);}reader.close();} catch (IOException e) {e.printStackTrace();}return html.toString();}// 提取图片URLpublic static String[] extractImgUrls(String html) {String[] imgUrls = html.split("<img");String[] result = new String[imgUrls.length - 1];for (int i = 1; i < imgUrls.length; i++) {String imgUrl = imgUrls[i].substring(imgUrls[i].indexOf("src=") + 5);imgUrl = imgUrl.substring(0, imgUrl.indexOf("\""));result[i - 1] = imgUrl;}return result;}// 下载图片到本地public static void downloadImage(String imgUrl, String saveDir) {try {URL url = new URL(imgUrl);HttpURLConnection conn = (HttpURLConnection) url.openConnection();conn.setRequestMethod("GET");conn.setConnectTimeout(5 * 1000);InputStream inStream = conn.getInputStream();byte[] data = readInputStream(inStream);File file = new File(saveDir + imgUrl.substring(imgUrl.lastIndexOf("/") + 1));FileOutputStream outStream = new FileOutputStream(file);outStream.write(data);outStream.close();} catch (IOException e) {e.printStackTrace();}}// 读取输入流并转换为字节数组public static byte[] readInputStream(InputStream inputStream) throws IOException {ByteArrayOutputStream outputStream = new ByteArrayOutputStream();byte[] buffer = new byte[1024];int len;while ((len = inputStream.read(buffer)) != -1) {outputStream.write(buffer, 0, len);}inputStream.close();return outputStream.toByteArray();}
}

这个程序首先读取指定网址的HTML源码，然后从中提取出所有的图片URL。最后，程序利用 Java 的 IO 功能下载这些图片并保存到指定的本地文件夹中。

需要注意的是，该程序只是一个简单的演示，实际使用时需要注意合法性和合理性问题，比如设置超时时间、判断文件是否存在等。此外，爬虫在爬取网站时需要遵守网站的爬取协议和法律法规，不能侵犯他人的权益。