docs: public static ExqlPattern compile(String pattern) {
  
          // 从缓存中获取编译好的语句
          ExqlPattern compiledPattern = cache.get(pattern);
          if (compiledPattern == null) {
  
              // 输出日志
              if (logger.isDebugEnabled()) {
                  logger.debug("EXQL pattern compiling:\n    pattern: " + pattern);
              }
  
              // 重新编译语句
              ExqlCompiler compiler = new ExqlCompiler(pattern);
              compiledPattern = compiler.compile();
  
              // 语句的缓存
              cache.putIfAbsent(pattern, compiledPattern);
          }
  
          return compiledPattern;
      }