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：（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 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(); }}
本文只是提供一种方式，仅供参考，仅供参考，仅供参考！
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