3. The method according to claim 1 , wherein the detecting the feature text string according to a finite-state machine comprises: detecting the feature text string backward from the end of the feature text string based on the finite-state machine and by using a bad character shift technology.
3. The method according to claim 1 , wherein the detecting the feature text string according to a finite-state machine comprises: detecting the feature text string backward from the end of the feature text string based on the finite-state machine and by using a bad character shift technology. 4. The method according to claim 3 , wherein the detecting the feature text string backward based on the finite-state machine and by using a bad character shift technology comprises: step a: determining a shortest string in the finite-state machine, and moving the finite-state machine backward from the end of the feature text string until an end character of the shortest string is aligned with an end character of the feature text string; step b: determining whether an initial character of a common prefix matches a first character of the feature text string aligned with the common prefix; step c: determining, based on the finite-state machine and starting from a character aligned with the initial character of the common prefix, whether a keyword exists in the feature text string if the initial character of the common prefix matches the first character of the feature text string aligned with the common prefix; and increasing the frequency of occurrence of the keyword by 1 and moving the finite-state machine backward by a length corresponding to a longest string if the keyword exists; or step d: determining whether a character matching the first character exists in the finite-state machine if the initial character of the common prefix does not match the first character of the feature text string aligned with the common prefix; moving the finite-state machine backward if the character matching the first character exists, until the character matching the first character in the finite-state machine is aligned with the first character, and determining, based on the finite-state machine and starting from a character aligned with the initial character of the common prefix, whether a keyword exists in the feature text string; and increasing the frequency of occurrence of the keyword by 1 and moving the finite-state machine backward by a length corresponding to a longest string if the keyword exists; and step e: executing step b to step d repeatedly until the common prefix reaches the beginning of the feature text string.