Java负载均衡服务器实现上传文件同步

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：https://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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