What exactly does URLConnection.setDoOutput() affect?

Question

There's setDoOutput() in URLConnection. According to documentation I should

Set the DoOutput flag to true if you intend to use the URL connection for output, false if not.

Now I'm facing exactly this problem - the Java runtime converts the request to POST once setDoOutput(true) is called and the server only responds to GET requests. I want to understand what happens if I remove that setDoOutput(true) from the code.

What exactly will this affect? Suppose I set it to false - what can I do now and what can't I do now? Will I be able to perform GET requests? What is "output" in context of this method?

score 109 · Accepted Answer · answered Dec 21 '11 at 09:59

109

You need to set it to true if you want to send (output) a request body, for example with POST or PUT requests. With GET, you do not usually send a body, so you do not need it.

Sending the request body itself is done via the connection's output stream:

conn.getOutputStream().write(someBytes);

answered Dec 21 '11 at 09:59

Thilo

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What if I'm downloading an image ? – Jaydev May 13 '16 at 08:29
Downloading? Or uploading? – Thilo May 13 '16 at 08:43

Petar Minchev · Answer 2 · 2011-12-21T10:01:07.140

34

setDoOutput(true) is used for POST and PUT requests. If it is false then it is for using GET requests.

edited Dec 21 '11 at 10:01

answered Dec 21 '11 at 09:56

Petar Minchev

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ok, how can I then force this connection to do PUT since server on the other side is accepting only PUT requests, not POST... ? – ante.sabo Jul 05 '12 at 10:54
What if I'm downloading an image ? – Jaydev May 13 '16 at 08:30
Why is it named `setDoOutput`? Not a very intuitive name – Siddhartha Jan 29 '21 at 08:22

score 2 · Answer 3 · answered Feb 10 '16 at 15:44

Adding a comment, if you have a long lasting connection and you send both GETs and POSTs, this is what I do:

if (doGet) {    // some boolean
    con.setDoOutput(false); // reset any previous setting, if con is long lasting
    con.setRequestMethod("GET");
}
else {
    con.setDoOutput(true);  // reset any previous setting, if con is long lasting
    con.setRequestMethod("POST");
}

And to avoid making the connection long lasting, close it each time.

if (doClose)    // some boolean
    con.setRequestProperty("Connection", "close");

con.connect();              // force connect request

score 0 · Answer 4 · answered Dec 21 '11 at 09:56

0

public void setDoOutput( boolean dooutput )

It takes a value as the parameter and sets this value of the doOutput field for this URLConnection to the specified value.

A URL connection can be used for input and/or output. Set the DoOutput flag to true if you intend to use the URL connection for output, false if not. The default is false.

answered Dec 21 '11 at 09:56

Mithun Sasidharan

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I've read that in the documentation before asking. The reason I'm asking is I don't get the implications of those. – sharptooth Dec 21 '11 at 10:00
If you want to write to a connection object you got to set the serDoOutput true – Mithun Sasidharan Dec 21 '11 at 10:15

What exactly does URLConnection.setDoOutput() affect?

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