1. A file storage system, comprising: a storage management apparatus and an adapter, wherein: the storage management apparatus is configured to receive an operation instruction sent by a user interface apparatus; if the operation instruction is a storage instruction for storing a first file and the storage instruction comprises an identifier of the first file, determine a first public cloud storage system for storing the first file among multiple public cloud storage systems and send a storage invoking command to a first adapter corresponding to the first public cloud storage system, so that the first adapter stores the first file in the first public cloud storage system; receive a first storage position sent by the first adapter, and store, in a file position table, a correspondence relationship between the identifier of the first file and the first storage position, where the first storage position is sent by the first public cloud storage system to the first adapter, the first storage position is a storage position of the first file in the first public cloud storage system, and the file position table stores a correspondence relationship between an identifier of a file and a storage position of the file; and if the operation instruction is a read instruction for reading a second file, and the read instruction comprises an identifier of the second file, determine, according to the identifier of the second file and the correspondence relationship, in the file position table, between the identifier of the file and the storage position of the file, a second storage position corresponding to storage of the second file, and send, according to the second storage position, a read-out invoking command to a second adapter corresponding to the second storage position, so that the second adapter acquires, according to the second storage position, the second file from a second public cloud storage system; receive the second file sent by the second adapter, and send the second file to the user interface apparatus; and the adapter is configured to receive the operation instruction sent by the storage management apparatus; if the operation instruction is the storage invoking command, store the first file in the first public cloud storage system and receive the first storage position of the first file in the first public cloud storage system, wherein the first storage position is returned by the first public cloud storage system, and the storage invoking command comprises the identifier of the first file; send the first storage position to the storage management apparatus, so that the storage management apparatus stores, in the file position table, the correspondence relationship between the identifier of the first file and the first storage position; and, if the operation instruction is the read-out invoking command, acquire, according to the second storage position, the second file from the second public cloud storage system, and send the second file to the storage management apparatus, wherein the read-out invoking command is sent after the storage management apparatus determines the second storage position according to the identifier of the second file and the correspondence relationship, in the file position table, between the identifier of the file and the storage position of the file.