为什么bufferReader在readLine（）上返回null

Question

I'm creating a BufferReader from InputStreamReader which loads response from webservice like this:

HttpURLConnection c = (HttpURLConnection) new URL(url).openConnection();
try {
    InputStream in = c.getInputStream();
    BufferedReader reader = new BufferedReader(new InputStreamReader(in));

    // returns null
    String line = reader.readLine();

    // correctly instantiates Article object
    Article article = new Gson().fromJson(reader, Article.class); 

However, for some reason, reader.readLine(); returns null , although the data successfully came from the server - I know that because Article object is correctly instantiated from the returned JSON. What could be the reason for returning null ?

Answer 1

Hm, that's odd... It worked perfectally fine for me when I did this:

File file = new File("plugin.yml");
BufferedReader reader = new BufferedReader(new FileReader(file));
String line;

while((line = reader.readLine()) != null) {
    System.out.println(line);
}

reader.close();

I know, you have stated that you have tested everything with the System.out.println(stuff), but I'll still ask the most basic questions and maybe the problem is hidden somewhere in there: Does it even enter the method? Is the file correctly spelled (also from where you add log to the log)? Does it work, if you use the Scanner to read the file?

Scanner scan = new Scanner(file);
String line;

while(scan.hasNextLine()) {
    line = scan.nextLine();
    //...
}

scan.close();

These are probably all silly questions, but it might help. As for now, I can't see any problems in your code.

Answer 2

I would assume you missed to set the connection output to true. Furthermore I'd do it something like this:

try {
  URL url = new URL("http://im-an-url.com");
  HttpURLConnection c = (HttpURLConnection) url.openConnection();
  c.setDoOutput(true);
  OutputStreamWriter wr = new OutputStreamWriter(c.getOutputStream());
  //do whatever you like here with the StreamWriter
  wr.close()
}

Answer 3

HttpURLConnection c = (HttpURLConnection) new URL(url).openConnection();
try {
c.connect();
if (c.getResponseCode == 200) {


InputStream in = c.getInputStream();
BufferedReader reader = new BufferedReader(new InputStreamReader(in));

// returns null
String line = reader.readLine();

// correctly instantiates Article object
Article article = new Gson().fromJson(reader, Article.class); 
 }

make sure the net stream has end tag \\r\\n if you use readLine method, or you can use BufferOutputStream