Develop Reference

Clarification about REST request in Java and output/input streams

I have to implement a post request in plain Java.
I have read the following question:
How to make a post request to a json RESTful Service from Java?
this is a part of the example
String url = "https://myStore.com/REST-API/";
String requestBody = "{\"searchProduct\": \"" + searchProduct + "\"}";
URL obj = new URL(url);
HttpsURLConnection connection = (HttpsURLConnection) obj
.openConnection();
connection.setDoOutput(true);
connection.setRequestMethod("POST");
connection.setRequestProperty("Content-Type", "application/json");
OutputStream outputStream = connection.getOutputStream();
outputStream.write(requestBody.getBytes());
My question is: why the parameters are written on the output stream? As far as I know, output stream is for collecting the output of a request, not to make it.
So just a curiosity, consider that I am obviously not skilled on this.

First let explain how HttpConnectionURL works.
When you want to request data from a server,
you first create a connection to that server.
Then you write data to the connection (request)
and finally read data from the connection (response).
So to write data to the connection you get a reference to the Connection's OutputStream and write data to it.
OutputStreamWriter writer = new OutputStreamWriter(
connection.getOutputStream());
writer.write("message=" + message);
To read data from the connection you get a reference to the Connection's InputStream and read data from it.
InputStreamReader reader = new InputStreamReader(connection.getInputStream());
reader.read();
Generally you use OutputStream when data is flowing out of your program (to file,network etc.,) and InputStream when data is flowing into your program (from file,network etc.,).
I think this will give you the clarity you are looking for.
This answer explains in detail how HttpConnectionURL works

The goal of InputStream and OutputStream is to abstract streams. By stream, I mean the way of the processed data (Input of the program or Output)
If the application receives information from the stream, use the InputStream. If it sends data then OutputStream
InputStreamused to read data from a source.
var input = new FileInputStream("input.txt");// Read the data
OutputStreamused for writing data to a destination.
var output = new FileOutputStream("output.txt");// Write the data
You should read answers in the related question : There are more explanations.

POST request is not sent

I have a short Android-Java client program which sends a basic information to bottle-python server with POST method. In the first version of code, server does not show anything. However, In the second version it works but I cannot understand what this additional line do because it has anything to do with posting content. I really appreciate if someone helps me figure this out.(There is nothing wrong with the server code since I can properly send request with python requests and my browsers).
This is the first version of client code:
String url = "http://192.168.1.23:8080/";
URL obj = new URL(url);
HttpURLConnection con = (HttpURLConnection) obj.openConnection();
con.setDoOutput(true);
OutputStream os = con.getOutputStream();
PrintStream myPusher = new PrintStream(os );
myPusher.print("param1=hey");
Second version:
String url = "http://192.168.1.23:8080/";
URL obj = new URL(url);
HttpURLConnection con = (HttpURLConnection) obj.openConnection();
con.setDoOutput(true);
OutputStream os = con.getOutputStream();
PrintStream myPusher = new PrintStream(os );
myPusher.print("param1=hey");
InputStream in= con.getInputStream(); //Nothing changed but only this additional line
Bottle(python) server:
#app.route('/', method="POST")
def hello():
print("it works")
name = request.forms.get("param1")
print(name)
return name
#app.route('/')
def hello():
i=0
print("it works")
run(app, host="192.168.1.23", port=8080)
With first client code server shows nothing.
With second code server shows:
it works
hey
192.168.1.24 - - [31/Dec/2018 17:10:28] "POST / HTTP/1.1" 200 3
Which is as I expected.

With your first code snippet the output stream is still open. So the server does not know if it got the complete request. Probably just closing the stream would work as well.
However, I would make at least a call to getResponseCode to see the outcome of the request.

Your java code seems incomplete for sending a post request.
I think by using this code, you can make it work for yourself.

The PrintStream is a buffered type, this means you should add a flush operation after each print(), or use println() instead.

writing to a file kept in ftp server

I have a requirement in which I have to write to files kept in FTP server using java ,I cant write to a file in the local server and then transfer it to ftp due to sensitivity of the data,can anyone share some thoughts/links on this.
Any Help will be greatly appreciated.
Apology for not posting my code snippet earlier below is the code I wrote
Student stu=new Student();
stu.setName("xyz");
stu.setRoll("12");
ftpClient.changeWorkingDirectory("/mydirectory/release/");
//abc.txt is the file on the server
FileOutputStream fos=(FileOutputStream)ftpClient.appendFileStream("abc.txt");
ObjectOutputStream oos = new ObjectOutputStream(fos);
oos.writeObject(stu);
Iam not getting any exception ,but also not able to write into the file..
yes I want to upload bytes via ftp from memory..
Thanks

I got the solution,I had to use url instead of ftpClient
URL url = new URL("ftp://user:pass#myftp.abc.com/myFile.txt;type=i");
URLConnection urlc = url.openConnection();
OutputStream os = urlc.getOutputStream(); // To upload
OutputStream buffer = new BufferedOutputStream(os);
ObjectOutput output = new ObjectOutputStream(buffer);
output.writeObject(myObject);
buffer.close();
os.close();
output.close();

It looks like Apache's FTPClient class, documented here, will do what you want.

Cannot upload file to a server

I'm using a function called UploadFFGS and this is its content:
URL url = new URL("http://linkedme.com/filebet.txt");
URLConnection ucn = url.openConnection();
HttpURLConnection connection = (HttpURLConnection) url.openConnection();
connection = (HttpURLConnection) url.openConnection();
FileInputStream is = new FileInputStream("filebet.txt"); //before I download the same file because I must edit it and upload the new version
OutputStream ostream = connection.getOutputStream();
PrintWriter pwriter = new PrintWriter(ostream);
pwriter.print(jTextArea1.getText());
pwriter.close();
This program never uploads the file filebet I have on my desktop to my link (http://linkedme.com/filebet.txt). Any ideas? I call it in this way:
try {
UploadFFGS();
}
catch (MalformedURLException ex) {
Logger.getLogger(xGrep.class.getName()).log(Level.SEVERE, null, ex);
} catch (IOException ex) {
Logger.getLogger(xGrep.class.getName()).log(Level.SEVERE, null, ex);
}
Also, NetBeans gives me this error: "java.net.ProtocolException: cannot write to a URLConnection if doOutput=false - call setDoOutput(true)".

Your approach won't work because your API endpoint (most likely) is a regular file rather than an interpreted script. The endpoint must provide a API by means of which you upload a file (POST/PUT etc).

I have a different solution. Maybe this will be useful for someone.
Just have a look at your advanced proxy settings in your web browser.
System engineers in our company had changed the proxy settings but I was not aware of it.
This error cost me 3 work-days. I got this doOutput error while writing a ftp upload project in my company. I tried everything like adding conn.setDoOutput(true) or 'fifty shades' of similar solutions but non of them saved me.
But, after I changed my proxy settings to correct ones, the error dissapeared and now I am able to upload my files through ftp using urlConnection in java.
I used the code in the link below to make an upload process, and did not add anything except host, port, user and password.
http://www.ajaxapp.com/2009/02/21/a-simple-java-ftp-connection-file-download-and-upload/

Reading from a URLConnection

I have a php page in my server that accepts a couple of POST requests and process them. Lets say it's a simple page and the output is simply an echoed statement. With the URLConnection I established from a Java program to send the POST request, I tried to get the input using the input stream got through connection.getInputStream(). But All I get is the source of the page(the whole php script) and not the output it produces. We shall avoid socket connections here. Can this be done with Url connection or HttpRequest? How?
class htttp{
public static void main(String a[]) throws IOException{
URL url=new URL("http://localhost/test.php");
URLConnection conn = url.openConnection();
//((HttpURLConnection) conn).setRequestMethod("POST");
conn.setDoOutput(true);
conn.setDoInput(true);
OutputStreamWriter wr = new OutputStreamWriter(conn.getOutputStream());
wr.write("Hello");
wr.flush();
wr.close();
InputStream ins = conn.getInputStream();
InputStreamReader isr = new InputStreamReader(ins);
BufferedReader in = new BufferedReader(isr);
String inputLine;
String result = "";
while( (inputLine = in.readLine()) != null )
result += inputLine;
System.out.print(result);
}
}
I get the whole source of the webpage test.php in result. But I want only the output of the php script.

The reason you get the PHP source itself, rather than the output it should be rendering, is that your local HTTP server - receiving your request targeted at http://localhost/test.php - decided to serve back the PHP source, rather than forward the HTTP request to a PHP processor to render the output.
Why this happens? that has to do with your HTTP server's configuration; there might be a few reasons for that. For starters, you should validate your HTTP server's configuration.
Which HTTP server are you using on your machine?
What happens when you browse http://localhost/test.php through your browser?

The problem here is not the Java code - the problem lies with the web server. You need to investigate why your webserver is not executing your PHP script but sending it back raw. You can begin by testing using a simple PHP scipt which returns a fixed result and is accessed using a GET request (from a web browser). Once that is working you can test using the one that responds to POST requests.