Question

这更多是与接口/功能/闭合/类型/ ...有关的通用Go问题，但具有执行I / O的具体用例。

给出一个io.Reader变量，我想使用自定义io.ReadCloser实现创建一个Close()。

var file os.File
file = ... // some File which needs to be closed

var reader io.Reader
reader = ... // get Reader from somewhere

var readCloser io.ReadCloser
readCloser = ... // how to create a ReadCloser here?

在Java中，我会写类似的东西：

readCloser = new io.ReadCloser() {
    Read(p []byte) {
        reader.Read(p);
    }

    Close() {
        // my custom close implementation
        file.Close()
    }    
}

// now pass readCloser around as needed

如何使用Go做到这一点？

Answer 1

一种方法是创建自己的类型，将io.Reader与 io.Closer并实现io.ReadCloser接口。像这样：

type ReadCloseCombiner struct {
    io.Reader
    io.Closer
}

func (rcc ReadCloseCombiner) Read(p []byte) (n int, err error) {
    return rcc.Reader.Read(p)
}

func (rcc ReadCloseCombiner) Close() error {
    return rcc.Closer.Close()
}

并像这样使用它：

var file *os.File
file = ... // some File which needs to be closed

var reader io.Reader
reader = ... // get Reader from somewhere

var readCloser io.ReadCloser
readCloser = ReadCloseCombiner{reader, file}

// now pass readCloser around as needed
readCloser.Read(...)
readCloser.Close()

如果您想要更灵活的东西，我会考虑使用具有读取和关闭功能的类型，然后可以将其传递给匿名函数（在您的情况下甚至是reader.Read / file.Close）。

Answer 2

从http.HandlerFunc得到提示，我想到了以下

package main

import (
    "bytes"
    "fmt"
    "io"
    "strings"
)

// ReadData reads data from an io.Reader
func ReadData(r io.Reader) {
    buf := new(bytes.Buffer)
    buf.ReadFrom(r)
    s := buf.String()
    fmt.Printf("read : %s \n", s)
}

// ReaderFunc takes a function and returns io.Reader
type ReaderFunc func([]byte) (int, error)

func (r ReaderFunc) Read(b []byte) (int, error) {
    return r(b)
}

func main() {
    // invoking ReadData with a regular io.Reader
    r := strings.NewReader("data 123")
    ReadData(r)

    // invoking ReadData with an anonymous io.Reader
    r = strings.NewReader("data 456")
    ReadData(ReaderFunc(func(b []byte) (int, error) {
        return r.Read(b)
    }))
}

如何在Java中编写等效于匿名类的内容？

2 个答案: