过滤器模式

过滤器模式

一、简介

过滤器模式（Filter Pattern）或标准模式（Criteria Pattern）是一种设计模式，这种模式允许开发人员使用不同的标准来过滤一组对象，通过逻辑运算以解耦的方式把它们连接起来。这种类型的设计模式属于结构型模式，它结合多个标准来获得单一标准。

二、代码

package mainimport (
"errors"
"fmt"
"log"
"strconv"
"strings"
)// Request is the input of the filter
type Request interface{}// Response is the output of the filter
type Response interface{}// Filter interface is the definition of the data processing components
// Pipe-Filter structure
type Filter interface {
Process(data Request) (Response, error)
}type SplitFilter struct {
delimiter string
}func NewSplitFilter(delimiter string) *SplitFilter {
return &SplitFilter{delimiter}
}func (sf *SplitFilter) Process(data Request) (Response, error) {
str, ok := data.(string) //检查数据格式/类型，是否可以处理
if !ok {
return nil, fmt.Errorf("input data must be string")
}
parts := strings.Split(str, sf.delimiter)
return parts, nil
}type ToIntFilter struct {
}func NewToIntFilter() *ToIntFilter {
return &ToIntFilter{}
}func (tif *ToIntFilter) Process(data Request) (Response, error) {
parts, ok := data.([]string)
if !ok {
return nil, fmt.Errorf("input data should be []string")
}
ret := make([]int, 0)
for _, part := range parts {
s, err := strconv.Atoi(part)
if err != nil {
return nil, err
}
ret = append(ret, s)
}
return ret, nil
}type SumFilter struct {
}func NewSumFilter() *SumFilter {
return &SumFilter{}
}func (sf *SumFilter) Process(data Request) (Response, error) {
elms, ok := data.([]int)
if !ok {
return nil, errors.New("input data should be []int")
}
ret := 0
for _, elem := range elms {
ret += elem
}
return ret, nil
}type Pipeline struct {
Name    string
Filters *[]Filter
}func NewPipeline(name string, filters ...Filter) *Pipeline {
return &Pipeline{
Name:    name,
Filters: &filters,
}
}// call each filter's process function
func (p *Pipeline) Process(data Request) (Response, error) {
var ret interface{}
var err error
for _, filter := range *p.Filters {
ret, err = filter.Process(data)
if err != nil {
return ret, err
}
data = ret
}
return ret, err
}func main() {
//例子中将字符串分割，再转成int，再求和
split := NewSplitFilter(",")
converter :=NewToIntFilter()
sum := NewSumFilter()
p :=NewPipeline("p1", split, converter, sum)
ret, err := p.Process("4,5,6")
if err != nil {
log.Fatal(err)
}
if ret != 15 {
log.Fatalf("The expected is 6, but the actual is %d", ret)
}
fmt.Println(ret)
}