Java如何实现负载均衡服务器上的文件上传同步功能？

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负载服务器Z，应用服务器A和服务器B，A服务器上传的附件如何在B服务器上下载？这个问题可以通过以下步骤解决：

1. 建立网络连接：确保服务器A和服务器B之间有稳定的网络连接。

2.数据传输协议：选择合适的数据传输协议，如HTTP、FTP或SFTP等，以确保数据传输的安全和可靠性。

3.数据存储：在服务器A上创建一个共享存储区域，用于存放上传的附件。

4.访问权限：为服务器B设置访问权限，确保只有授权的用户或服务器可以访问这些附件。

5.下载脚本：在服务器B上编写脚本或使用工具，如curl或wget，来自动化附件的下载过程。

6.下载过程：通过脚本或工具，定期或按需从服务器A的共享存储区域下载附件到服务器B。

具体操作示例（以使用curl为例）：

bash

#!/bin/bash

设置服务器A的地址和上传附件的路径SERVER_A_URL=http://server-a.com/upload_path设置附件在服务器A上的名称ATTACHMENT_NAME=example_file.zip设置服务器B上的下载路径LOCAL_PATH=/path/to/download

使用curl下载附件curl -o $LOCAL_PATH/$ATTACHMENT_NAME $SERVER_A_URL/$ATTACHMENT_NAME

确保脚本有执行权限，并通过定时任务（如cron job）来定期运行此脚本。这样，服务器B就能定期从服务器A下载附件了。

负载服务器Z，应用服务器A 和B ，从A上传的附件，如何在B上下载下来？

这个问题我的解决思路如下（后来被一个装逼的面试官给批评了这种做法，不过我瞧不起他）

服务器A、B 上传附件的时候，将这个附件备份到服务器Z ，当A、B下载文件的时候，首先会在自己服务器的目录下寻找，如果找不到，就会从服务器Z 上下载一份到当前服务器。

服务器之间的文件备份通过sftp，参考：www.jb51.net/article/196008.htm（下文中的SftpCustom 类就是这个链接里的 “SFTP上传下载文件例子” 中的类）

这里主要介绍一下重写上传、下载的方法时应该添加的代码

上传文件，异步操作

new Thread(() -> { 　　SftpCustom fu = new SftpCustom(); 　　fu.upload(file.getAbsolutePath(), getFileName(fileDescr)); 　　fu.closeChannel(); }).start();

下载文件，先从当前服务器寻找

String tmpPath = roots[0].getPath() + '/' + getFileName(fileDescr); File file2 = new File(tmpPath); if (file2.exists()) { 　　return FileUtils.openInputStream(file2); } SftpCustom fu = new SftpCustom(); fu.download(getFileName(fileDescr), tmpPath); file2 = new File(tmpPath); inputStream = FileUtils.openInputStream(file2); fu.closeChannel(); return inputStream;

cuba 框架中重写上传文件类FileStorage.java 的代码如下：

package com.haulmont.cuba.core.app.custom; import com.google.common.util.concurrent.ThreadFactoryBuilder; import com.haulmont.cuba.core.app.FileStorageAPI; import com.haulmont.cuba.core.app.ServerConfig; import com.haulmont.cuba.core.entity.FileDescriptor; import com.haulmont.cuba.core.global.*; import com.haulmont.cuba.core.sys.AppContext; import com.haulmont.cuba.core.sys.SecurityContext; import org.apache.commons.io.FileUtils; import org.apache.commons.io.IOUtils; import org.apache.commons.lang.StringUtils; import org.slf4j.Logger; import org.slf4j.LoggerFactory; import javax.annotation.PostConstruct; import javax.annotation.PreDestroy; import javax.inject.Inject; import java.io.*; import java.nio.charset.StandardCharsets; import java.text.SimpleDateFormat; import java.util.ArrayList; import java.util.Calendar; import java.util.List; import java.util.concurrent.ExecutorService; import java.util.concurrent.Executors; import static com.haulmont.bali.util.Preconditions.checkNotNullArgument; public class FileStorage implements FileStorageAPI { private final Logger log = LoggerFactory.getLogger(FileStorage.class); @Inject protected UserSessionSource userSessionSource; @Inject protected TimeSource timeSource; @Inject protected Configuration configuration; protected boolean isImmutableFileStorage; protected ExecutorService writeExecutor = Executors.newFixedThreadPool(5, new ThreadFactoryBuilder().setNameFormat("FileStorageWriter-%d").build()); protected volatile File[] storageRoots; @PostConstruct public void init() { this.isImmutableFileStorage = configuration.getConfig(ServerConfig.class).getImmutableFileStorage(); } /** * INTERNAL. Don't use in application code. */ public File[] getStorageRoots() { if (storageRoots == null) { String conf = configuration.getConfig(ServerConfig.class).getFileStorageDir(); if (StringUtils.isBlank(conf)) { String dataDir = configuration.getConfig(GlobalConfig.class).getDataDir(); File dir = new File(dataDir, "filestorage"); dir.mkdirs(); storageRoots = new File[]{dir}; } else { List<File> list = new ArrayList<>(); for (String str : conf.split(",")) { str = str.trim(); if (!StringUtils.isEmpty(str)) { File file = new File(str); if (!list.contains(file)) list.add(file); } } storageRoots = list.toArray(new File[list.size()]); } } return storageRoots; } @Override public long saveStream(final FileDescriptor fileDescr, final InputStream inputStream) throws FileStorageException { checkFileDescriptor(fileDescr); File[] roots = getStorageRoots(); // Store to primary storage checkStorageDefined(roots, fileDescr); checkPrimaryStorageAccessible(roots, fileDescr); File dir = getStorageDir(roots[0], fileDescr); dir.mkdirs(); checkDirectoryExists(dir); final File file = new File(dir, getFileName(fileDescr)); checkFileExists(file); long size = 0; OutputStream os = null; try { os = FileUtils.openOutputStream(file); size = IOUtils.copyLarge(inputStream, os); os.flush(); writeLog(file, false); new Thread(() -> { SftpCustom fu = new SftpCustom(); fu.upload(file.getAbsolutePath(), getFileName(fileDescr)); fu.closeChannel(); }).start(); } catch (IOException e) { IOUtils.closeQuietly(os); FileUtils.deleteQuietly(file); throw new FileStorageException(FileStorageException.Type.IO_EXCEPTION, file.getAbsolutePath(), e); } finally { IOUtils.closeQuietly(os); } // Copy file to secondary storages asynchronously final SecurityContext securityContext = AppContext.getSecurityContext(); for (int i = 1; i < roots.length; i++) { if (!roots[i].exists()) { log.error("Error saving {} into {} : directory doesn't exist", fileDescr, roots[i]); continue; } File copyDir = getStorageDir(roots[i], fileDescr); final File fileCopy = new File(copyDir, getFileName(fileDescr)); writeExecutor.submit(new Runnable() { @Override public void run() { try { AppContext.setSecurityContext(securityContext); FileUtils.copyFile(file, fileCopy, true); writeLog(fileCopy, false); } catch (Exception e) { log.error("Error saving {} into {} : {}", fileDescr, fileCopy.getAbsolutePath(), e.getMessage()); } finally { AppContext.setSecurityContext(null); } } }); } return size; } protected void checkFileExists(File file) throws FileStorageException { if (file.exists() && isImmutableFileStorage) throw new FileStorageException(FileStorageException.Type.FILE_ALREADY_EXISTS, file.getAbsolutePath()); } protected void checkDirectoryExists(File dir) throws FileStorageException { if (!dir.exists()) throw new FileStorageException(FileStorageException.Type.STORAGE_INACCESSIBLE, dir.getAbsolutePath()); } protected void checkPrimaryStorageAccessible(File[] roots, FileDescriptor fileDescr) throws FileStorageException { if (!roots[0].exists()) { log.error("Inaccessible primary storage at {}", roots[0]); throw new FileStorageException(FileStorageException.Type.STORAGE_INACCESSIBLE, fileDescr.getId().toString()); } } protected void checkStorageDefined(File[] roots, FileDescriptor fileDescr) throws FileStorageException { if (roots.length == 0) { log.error("No storage directories defined"); throw new FileStorageException(FileStorageException.Type.STORAGE_INACCESSIBLE, fileDescr.getId().toString()); } } @Override public void saveFile(final FileDescriptor fileDescr, final byte[] data) throws FileStorageException { checkNotNullArgument(data, "File content is null"); saveStream(fileDescr, new ByteArrayInputStream(data)); } protected synchronized void writeLog(File file, boolean remove) { SimpleDateFormat df = new SimpleDateFormat("yyyy-MM-dd HH:mm:ss.SSS"); StringBuilder sb = new StringBuilder(); sb.append(df.format(timeSource.currentTimestamp())).append(" "); sb.append("[").append(userSessionSource.getUserSession().getUser()).append("] "); sb.append(remove ? "REMOVE" : "CREATE").append(" "); sb.append("\"").append(file.getAbsolutePath()).append("\"\n"); File rootDir; try { rootDir = file.getParentFile().getParentFile().getParentFile().getParentFile(); } catch (NullPointerException e) { log.error("Unable to write log: invalid file storage structure", e); return; } File logFile = new File(rootDir, "storage.log"); try { try (FileOutputStream fos = new FileOutputStream(logFile, true)) { IOUtils.write(sb.toString(), fos, StandardCharsets.UTF_8.name()); } } catch (IOException e) { log.error("Unable to write log", e); } } @Override public void removeFile(FileDescriptor fileDescr) throws FileStorageException { checkFileDescriptor(fileDescr); File[] roots = getStorageRoots(); if (roots.length == 0) { log.error("No storage directories defined"); return; } for (File root : roots) { File dir = getStorageDir(root, fileDescr); File file = new File(dir, getFileName(fileDescr)); if (file.exists()) { if (!file.delete()) { throw new FileStorageException(FileStorageException.Type.IO_EXCEPTION, "Unable to delete file " + file.getAbsolutePath()); } else { writeLog(file, true); } } } } protected void checkFileDescriptor(FileDescriptor fd) { if (fd == null || fd.getCreateDate() == null) { throw new IllegalArgumentException("A FileDescriptor instance with populated 'createDate' attribute must be provided"); } } @Override public InputStream openStream(FileDescriptor fileDescr) throws FileStorageException { checkFileDescriptor(fileDescr); File[] roots = getStorageRoots(); if (roots.length == 0) { log.error("No storage directories available"); throw new FileStorageException(FileStorageException.Type.FILE_NOT_FOUND, fileDescr.getId().toString()); } InputStream inputStream = null; for (File root : roots) { File dir = getStorageDir(root, fileDescr); File file = new File(dir, getFileName(fileDescr)); if (!file.exists()) { log.error("File " + file + " not found"); continue; } try { inputStream = FileUtils.openInputStream(file); break; } catch (IOException e) { log.error("Error opening input stream for " + file, e); } } if (inputStream != null) { return inputStream; } else { try { String tmpPath = roots[0].getPath() + '/' + getFileName(fileDescr); File file2 = new File(tmpPath); if (file2.exists()) { return FileUtils.openInputStream(file2); } SftpCustom fu = new SftpCustom(); fu.download(getFileName(fileDescr), tmpPath); file2 = new File(tmpPath); inputStream = FileUtils.openInputStream(file2); fu.closeChannel(); return inputStream; } catch (Exception e) { throw new FileStorageException(FileStorageException.Type.FILE_NOT_FOUND, fileDescr.getId().toString()); } } } @Override public byte[] loadFile(FileDescriptor fileDescr) throws FileStorageException { InputStream inputStream = openStream(fileDescr); try { return IOUtils.toByteArray(inputStream); } catch (IOException e) { throw new FileStorageException(FileStorageException.Type.IO_EXCEPTION, fileDescr.getId().toString(), e); } finally { IOUtils.closeQuietly(inputStream); } } @Override public boolean fileExists(FileDescriptor fileDescr) { checkFileDescriptor(fileDescr); File[] roots = getStorageRoots(); for (File root : roots) { File dir = getStorageDir(root, fileDescr); File file = new File(dir, getFileName(fileDescr)); if (file.exists()) { return true; } } return false; } /** * INTERNAL. Don't use in application code. */ public File getStorageDir(File rootDir, FileDescriptor fileDescriptor) { checkNotNullArgument(rootDir); checkNotNullArgument(fileDescriptor); Calendar cal = Calendar.getInstance(); cal.setTime(fileDescriptor.getCreateDate()); int year = cal.get(Calendar.YEAR); int month = cal.get(Calendar.MONTH) + 1; int day = cal.get(Calendar.DAY_OF_MONTH); return new File(rootDir, year + "/" + StringUtils.leftPad(String.valueOf(month), 2, '0') + "/" + StringUtils.leftPad(String.valueOf(day), 2, '0')); } public static String getFileName(FileDescriptor fileDescriptor) { return fileDescriptor.getId().toString() + "." + fileDescriptor.getExtension(); } @PreDestroy protected void stopWriteExecutor() { writeExecutor.shutdown(); } }

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