public FileManager build() {
            Requires.requireNonNull(this.storePath, "storePath");
            Requires.requireNonNull(this.fileType, "fileType");
            Requires.requireNonNull(this.logStoreFactory, "logStoreFactory");
            Requires.requireNonNull(this.fileSize, "fileSize");
            Requires.requireNonNull(this.allocateService, "allocateService");
            return new FileManager(fileType, fileSize, storePath, logStoreFactory, allocateService);
        }
Uses list to manage AbstractFile(Index,Segment) by logIndex and offset
@author hzh (642256541@qq.com)
jraft-extension/java-log-storage-impl/src/main/java/com/alipay/sofa/jraft/storage/file/FileManager.java