参考 Schouwenaars (2016)
Downloading a file from the Internet means sending a GET request and receiving the file you asked for. Internally, all the previously discussed functions use a GET request to download files.
这是 GET 请求最直观的定义。 通过网页链接下载文件，这都算是 GET 请求。
# Load the httr package
library(httr)
# Get the url, save response to resp
url <- "http://www.example.com/"
resp <- GET(url)
# Print resp
resp
## Response [http://www.example.com/]
## Date: 2019-02-20 07:11
## Status: 200
## Content-Type: text/html; charset=UTF-8
## Size: 1.27 kB
## <!doctype html>
## <html>
## <head>
## <title>Example Domain</title>
##
## <meta charset="utf-8" />
## <meta http-equiv="Content-type" content="text/html; charset=utf-8" />
## <meta name="viewport" content="width=device-width, initial-scale=1" />
## <style type="text/css">
## body {
## ...
resp 的内容，类似于 view source 出来的网页源代码。
library(httr)
# Get the url
url <- "http://www.omdbapi.com/?apikey=72bc447a&t=Annie+Hall&y=&plot=short&r=json"
# Print resp
resp <- GET(url)
resp
## Response [http://www.omdbapi.com/?apikey=72bc447a&t=Annie+Hall&y=&plot=short&r=json]
## Date: 2019-02-20 07:11
## Status: 200
## Content-Type: application/json; charset=utf-8
## Size: 929 B
# Print content of resp as text
content(resp, as = 'text')
## [1] "{\"Title\":\"Annie Hall\",\"Year\":\"1977\",\"Rated\":\"PG\",\"Released\":\"20 Apr 1977\",\"Runtime\":\"93 min\",\"Genre\":\"Comedy, Romance\",\"Director\":\"Woody Allen\",\"Writer\":\"Woody Allen, Marshall Brickman\",\"Actors\":\"Woody Allen, Diane Keaton, Tony Roberts, Carol Kane\",\"Plot\":\"Neurotic New York comedian Alvy Singer falls in love with the ditzy Annie Hall.\",\"Language\":\"English, German\",\"Country\":\"USA\",\"Awards\":\"Won 4 Oscars. Another 26 wins & 8 nominations.\",\"Poster\":\"https://m.media-amazon.com/images/M/MV5BZDg1OGQ4YzgtM2Y2NS00NjA3LWFjYTctMDRlMDI3NWE1OTUyXkEyXkFqcGdeQXVyMjUzOTY1NTc@._V1_SX300.jpg\",\"Ratings\":[{\"Source\":\"Internet Movie Database\",\"Value\":\"8.0/10\"},{\"Source\":\"Rotten Tomatoes\",\"Value\":\"97%\"},{\"Source\":\"Metacritic\",\"Value\":\"92/100\"}],\"Metascore\":\"92\",\"imdbRating\":\"8.0\",\"imdbVotes\":\"233,030\",\"imdbID\":\"tt0075686\",\"Type\":\"movie\",\"DVD\":\"28 Apr 1998\",\"BoxOffice\":\"N/A\",\"Production\":\"United Artists\",\"Website\":\"N/A\",\"Response\":\"True\"}"
# Print content of resp
content(resp)
## $Title
## [1] "Annie Hall"
##
## $Year
## [1] "1977"
##
## $Rated
## [1] "PG"
##
## $Released
## [1] "20 Apr 1977"
##
## $Runtime
## [1] "93 min"
##
## $Genre
## [1] "Comedy, Romance"
##
## $Director
## [1] "Woody Allen"
##
## $Writer
## [1] "Woody Allen, Marshall Brickman"
##
## $Actors
## [1] "Woody Allen, Diane Keaton, Tony Roberts, Carol Kane"
##
## $Plot
## [1] "Neurotic New York comedian Alvy Singer falls in love with the ditzy Annie Hall."
##
## $Language
## [1] "English, German"
##
## $Country
## [1] "USA"
##
## $Awards
## [1] "Won 4 Oscars. Another 26 wins & 8 nominations."
##
## $Poster
## [1] "https://m.media-amazon.com/images/M/MV5BZDg1OGQ4YzgtM2Y2NS00NjA3LWFjYTctMDRlMDI3NWE1OTUyXkEyXkFqcGdeQXVyMjUzOTY1NTc@._V1_SX300.jpg"
##
## $Ratings
## $Ratings[[1]]
## $Ratings[[1]]$Source
## [1] "Internet Movie Database"
##
## $Ratings[[1]]$Value
## [1] "8.0/10"
##
##
## $Ratings[[2]]
## $Ratings[[2]]$Source
## [1] "Rotten Tomatoes"
##
## $Ratings[[2]]$Value
## [1] "97%"
##
##
## $Ratings[[3]]
## $Ratings[[3]]$Source
## [1] "Metacritic"
##
## $Ratings[[3]]$Value
## [1] "92/100"
##
##
##
## $Metascore
## [1] "92"
##
## $imdbRating
## [1] "8.0"
##
## $imdbVotes
## [1] "233,030"
##
## $imdbID
## [1] "tt0075686"
##
## $Type
## [1] "movie"
##
## $DVD
## [1] "28 Apr 1998"
##
## $BoxOffice
## [1] "N/A"
##
## $Production
## [1] "United Artists"
##
## $Website
## [1] "N/A"
##
## $Response
## [1] "True"
… the
content()function by default, if you don’t specify theasargument, figures out what type of data you’re dealing with and parses it for you.
as 一般不用设置，httr 的函数会自动判断。
httrconverts the JSON response body automatically to an R list