关于golang:聊聊dubbogoproxy的jtypes

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本文次要钻研一下 dubbo-go-proxy 的 jtypes

dubbo-go-proxy/pkg/common/constant/jtypes.go

// Object represents the java.lang.Object type
type Object interface{}

// JTypeMapper maps the java basic types to golang types
var JTypeMapper = map[string]reflect.Type{"string":           reflect.TypeOf(""),"java.lang.String": reflect.TypeOf(""),
    "char":             reflect.TypeOf(""),"short":            reflect.TypeOf(int32(0)),"int":              reflect.TypeOf(int32(0)),"long":             reflect.TypeOf(int64(0)),"float":            reflect.TypeOf(float64(0)),"double":           reflect.TypeOf(float64(0)),"boolean":          reflect.TypeOf(true),"java.util.Date":   reflect.TypeOf(time.Time{}),"date":             reflect.TypeOf(time.Time{}),"object":           reflect.TypeOf([]Object{}).Elem(),"java.lang.Object": reflect.TypeOf([]Object{}).Elem(),}

JTypeMapper 定义了个 map，key 为 java 类型，value 为 golang 的 reflect.Type

dubbo-go-proxy/pkg/client/dubbo/mapper.go

func mapTypes(jType string, originVal interface{}) (interface{}, error) {targetType, ok := constant.JTypeMapper[jType]
    if !ok {return nil, errors.Errorf("Invalid parameter type: %s", jType)
    }
    switch targetType {case reflect.TypeOf(""):
        return cast.ToStringE(originVal)
    case reflect.TypeOf(int32(0)):
        return cast.ToInt32E(originVal)
    case reflect.TypeOf(int64(0)):
        return cast.ToInt64E(originVal)
    case reflect.TypeOf(float64(0)):
        return cast.ToFloat64E(originVal)
    case reflect.TypeOf(true):
        return cast.ToBoolE(originVal)
    case reflect.TypeOf(time.Time{}):
        return cast.ToBoolE(originVal)
    default:
        return originVal, nil
    }
}

mapTypes 办法先依据 jType 从 JTypeMapper 取出对应的 golang 的 reflect.Type，而后挨个依据这个类型应用 cast 类库进行转换，转成 golang 的 interface{}

github.com/spf13/cast@v1.3.1/caste.go

// ToStringE casts an interface to a string type.
func ToStringE(i interface{}) (string, error) {i = indirectToStringerOrError(i)

    switch s := i.(type) {
    case string:
        return s, nil
    case bool:
        return strconv.FormatBool(s), nil
    case float64:
        return strconv.FormatFloat(s, 'f', -1, 64), nil
    case float32:
        return strconv.FormatFloat(float64(s), 'f', -1, 32), nil
    case int:
        return strconv.Itoa(s), nil
    case int64:
        return strconv.FormatInt(s, 10), nil
    case int32:
        return strconv.Itoa(int(s)), nil
    case int16:
        return strconv.FormatInt(int64(s), 10), nil
    case int8:
        return strconv.FormatInt(int64(s), 10), nil
    case uint:
        return strconv.FormatUint(uint64(s), 10), nil
    case uint64:
        return strconv.FormatUint(uint64(s), 10), nil
    case uint32:
        return strconv.FormatUint(uint64(s), 10), nil
    case uint16:
        return strconv.FormatUint(uint64(s), 10), nil
    case uint8:
        return strconv.FormatUint(uint64(s), 10), nil
    case []byte:
        return string(s), nil
    case template.HTML:
        return string(s), nil
    case template.URL:
        return string(s), nil
    case template.JS:
        return string(s), nil
    case template.CSS:
        return string(s), nil
    case template.HTMLAttr:
        return string(s), nil
    case nil:
        return "", nil
    case fmt.Stringer:
        return s.String(), nil
    case error:
        return s.Error(), nil
    default:
        return "", fmt.Errorf("unable to cast %#v of type %T to string", i, i)
    }
}

github.com/spf13/cast 提供了一系列的 cast 办法，用于将 interface{} 转换为指定的类型

JTypeMapper 定义了个 map，key 为 java 类型，value 为 golang 的 reflect.Type；mapTypes 办法先依据 jType 从 JTypeMapper 取出对应的 golang 的 reflect.Type，而后挨个依据这个类型应用 cast 类库进行转换，转成 golang 的 interface{}。