示例
var_dump(filter_var(true, FILTER_VALIDATE_BOOLEAN, FILTER_NULL_ON_FAILURE)); // 真正
var_dump(filter_var(false, FILTER_VALIDATE_BOOLEAN, FILTER_NULL_ON_FAILURE)); // 假
var_dump(filter_var(1, FILTER_VALIDATE_BOOLEAN, FILTER_NULL_ON_FAILURE)); // 真正
var_dump(filter_var(0, FILTER_VALIDATE_BOOLEAN, FILTER_NULL_ON_FAILURE)); // 假
var_dump(filter_var('1', FILTER_VALIDATE_BOOLEAN, FILTER_NULL_ON_FAILURE)); // 真正
var_dump(filter_var('0', FILTER_VALIDATE_BOOLEAN, FILTER_NULL_ON_FAILURE)); // 假
var_dump(filter_var('', FILTER_VALIDATE_BOOLEAN, FILTER_NULL_ON_FAILURE)); // 假
var_dump(filter_var(' ', FILTER_VALIDATE_BOOLEAN, FILTER_NULL_ON_FAILURE)); // 假
var_dump(filter_var('true', FILTER_VALIDATE_BOOLEAN, FILTER_NULL_ON_FAILURE)); // 真正
var_dump(filter_var('false', FILTER_VALIDATE_BOOLEAN, FILTER_NULL_ON_FAILURE)); // 假
var_dump(filter_var([], FILTER_VALIDATE_BOOLEAN, FILTER_NULL_ON_FAILURE)); // 空值
var_dump(filter_var(null, FILTER_VALIDATE_BOOLEAN, FILTER_NULL_ON_FAILURE)); // 假