setDoOutputtrue

setDoOutput(true) is a method of java.net.URLConnection and its subclass HttpURLConnection. It signals that the application intends to use the connection for output, i.e., to send data to the remote resource. This flag is commonly used when performing requests that include a body, such as POST or PUT.

When setDoOutput(true) is in effect, the typical usage pattern is to obtain an OutputStream via getOutputStream and write the request payload to it. After writing, the stream is closed and the response can be read from the connection’s input stream. The call to setDoOutput should be made before the connection is established (before connect() or before obtaining streams). Changing the flag after the connection has been opened may have no effect on the ongoing operation.

If the chosen request method or protocol does not support a request body, attempting to obtain or write to the output stream can result in a ProtocolException. The exact behavior can vary by protocol and implementation. For HTTP, developers commonly pair setDoOutput(true) with setRequestMethod("POST") or setRequestMethod("PUT") and set appropriate headers such as Content-Type to describe the payload.

In summary, setDoOutput(true) enables sending a body with a URL connection, signals the intent to output data, and is a prerequisite for writing data to the request. It is a preparatory step used in conjunction with obtaining an output stream, writing data, and then processing the corresponding response.