# 访问并读取页面数据

在下边这个程序中，数组中的url都将被访问：会发送一个简单的`http.Head()`请求查看返回值；它的声明如下：`func Head(url string) (r *Response, err error)`

返回状态码会被打印出来。

示例 15.7 [poll\_url.go](https://github.com/yangchuansheng/the-way-to-go_ZH_CN/tree/f30ab7d8c58f85840a0afb548024b93642b518d5/eBook/examples/chapter_15/poll_url.go)：

```go
package main

import (
    "fmt"
    "net/http"
)

var urls = []string{
    "http://www.google.com/",
    "http://golang.org/",
    "http://blog.golang.org/",
}

func main() {
    // Execute an HTTP HEAD request for all url's
    // and returns the HTTP status string or an error string.
    for _, url := range urls {
        resp, err := http.Head(url)
        if err != nil {
            fmt.Println("Error:", url, err)
        }
        fmt.Println(url, ": ", resp.Status)
    }
}
```

输出为：

```
http://www.google.com/ : 302 Found
http://golang.org/ : 200 OK
http://blog.golang.org/ : 200 OK
```

***译者注*** 由于国内的网络环境现状，很有可能见到如下超时错误提示：

```
Error: http://www.google.com/ Head http://www.google.com/: dial tcp 216.58.221.100:80: connectex: A connection attempt failed because the connected pa
rty did not properly respond after a period of time, or established connection failed because connected host has failed to respond.
```

在下边的程序中我们使用`http.Get()`获取网页内容； `Get`的返回值`res`中的`Body`属性包含了网页内容，然后我们用`ioutil.ReadAll`把它读出来：

示例 15.8 [http\_fetch.go](https://github.com/yangchuansheng/the-way-to-go_ZH_CN/tree/f30ab7d8c58f85840a0afb548024b93642b518d5/eBook/examples/chapter_15/http_fetch.go)：

```go
package main

import (
    "fmt"
    "io/ioutil"
    "log"
    "net/http"
)

func main() {
    res, err := http.Get("http://www.google.com")
    checkError(err)
    data, err := ioutil.ReadAll(res.Body)
    checkError(err)
    fmt.Printf("Got: %q", string(data))
}

func checkError(err error) {
    if err != nil {
        log.Fatalf("Get : %v", err)
    }
}
```

当访问不存在的网站时，这里有一个`CheckError`输出错误的例子：

```
2011/09/30 11:24:15 Get: Get http://www.google.bex: dial tcp www.google.bex:80:GetHostByName: No such host is known.
```

***译者注*** 和上一个例子相似，你可以把google.com更换为一个国内可以顺畅访问的网址进行测试

在下边的程序中，我们获取一个twitter用户的状态，通过`xml`包将这个状态解析成为一个结构：

示例 15.9 [twitter\_status.go](https://github.com/yangchuansheng/the-way-to-go_ZH_CN/tree/f30ab7d8c58f85840a0afb548024b93642b518d5/eBook/examples/chapter_15/twitter_status.go)

```go
package main

import (
    "encoding/xml"
    "fmt"
    "net/http"
)

/*这个结构会保存解析后的返回数据。
他们会形成有层级的XML，可以忽略一些无用的数据*/
type Status struct {
    Text string
}

type User struct {
    XMLName xml.Name
    Status  Status
}

func main() {
    // 发起请求查询推特Goodland用户的状态
    response, _ := http.Get("http://twitter.com/users/Googland.xml")
    // 初始化XML返回值的结构
    user := User{xml.Name{"", "user"}, Status{""}}
    // 将XML解析为我们的结构
    xml.Unmarshal(response.Body, &user)
    fmt.Printf("status: %s", user.Status.Text)
}
```

输出：

```
status: Robot cars invade California, on orders from Google: Google has been testing self-driving cars ... http://bit.ly/cbtpUN http://retwt.me/97p<exit code="0" msg="process exited normally"/>
```

**译者注** 和上边的示例相似，你可能无法获取到xml数据，另外由于go版本的更新，`xml.Unmarshal`函数的第一个参数需是\[]byte类型，而无法传入`Body`。

我们会在[章节15.4](https://ryanyang.gitbook.io/the-way-to-go-zh-cn/di-san-bu-fen-go-gao-ji-bian-cheng/15.0/15.4)中用到`http`包中的其他重要的函数：

* `http.Redirect(w ResponseWriter, r *Request, url string, code int)`：这个函数会让浏览器重定向到url（是请求的url的相对路径）以及状态码。
* `http.NotFound(w ResponseWriter, r *Request)`：这个函数将返回网页没有找到，HTTP 404错误。
* `http.Error(w ResponseWriter, error string, code int)`：这个函数返回特定的错误信息和HTTP代码。
* 另`http.Request`对象的一个重要属性`req`：`req.Method`，这是一个包含`GET`或`POST`字符串，用来描述网页是以何种方式被请求的。

go为所有的HTTP状态码定义了常量，比如：

```
http.StatusContinue        = 100
http.StatusOK            = 200
http.StatusFound        = 302
http.StatusBadRequest        = 400
http.StatusUnauthorized        = 401
http.StatusForbidden        = 403
http.StatusNotFound        = 404
http.StatusInternalServerError    = 500
```

你可以使用`w.header().Set("Content-Type", "../..")`设置头信息

比如在网页应用发送html字符串的时候，在输出之前执行`w.Header().Set("Content-Type", "text/html")`。

练习 15.4：扩展 http\_fetch.go 使之可以从控制台读取url，使用[章节12.1](https://ryanyang.gitbook.io/the-way-to-go-zh-cn/di-san-bu-fen-go-gao-ji-bian-cheng/12.0/12.1)学到的接收控制台输入的方法 （[http\_fetch2.go](https://github.com/yangchuansheng/the-way-to-go_ZH_CN/tree/f30ab7d8c58f85840a0afb548024b93642b518d5/eBook/examples/chapter_15/http_fetch2.go)）

练习 15.5：获取json格式的推特状态，就像示例 15.9（twitter\_status\_json.go）

## 链接

* [目录](https://github.com/yangchuansheng/the-way-to-go_ZH_CN/tree/f30ab7d8c58f85840a0afb548024b93642b518d5/eBook/directory.md)
* 上一章：[一个简单的网页服务器](https://ryanyang.gitbook.io/the-way-to-go-zh-cn/di-san-bu-fen-go-gao-ji-bian-cheng/15.0/15.2)
* 下一节：[写一个简单的网页应用](https://ryanyang.gitbook.io/the-way-to-go-zh-cn/di-san-bu-fen-go-gao-ji-bian-cheng/15.0/15.4)


---

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