Number Format Exception in Java Servlet

Question

I have made a simple servlet in Eclipse running on Tomcat server.

I am running a simple java application which passes a string message=20 to the servlet. The servlet gets the data. I am using

String name= request.getParameter("message");

to get the passed string. When I return the name value back to the application, I am able to get it back. But when I try to process the string name:

int val=Integer.parseInt(name);

I get NumberFormatException . I cannot figure out what the problem is. I have been able to get the value of name variable back from the servlet, but why can't I use it?

The Code I am using is as follows:

CLIENT SIDE CODE

URL url = new URL("http://localhost:8080/DemoServer/demoservelet");

URLConnection conn = url.openConnection();

conn.setDoOutput(true);

BufferedWriter out = new BufferedWriter( new OutputStreamWriter( conn.getOutputStream() ) );

out.write("message=20");

SERVLET CODE

String username = request.getParameter("message").toString();

int val=Integer.parseInt(username);  //get error msg on this line

response.setContentType("text/html");

PrintWriter out = response.getWriter();

out.println("Passed val :"+ username+username.length());


}

I am getting error on the conversion. One more thing on return I am getting a length value of 4 which also does not make any sense?

Please help me regarding this.

Answer 1

Are you trying to use GET-style parameter passing or PUSH-style parameter passing?

GET-style passing tacks the parameter on the end of the URL like so:

http://localhost:8080/DemoServer/demoservelet?value=20

A URL like this can be assembled fairly easily. You only need to change your URL-creation line, and can remove the two lines related to opening a BufferedWriter:

URL url = new URL(String.format("http://localhost:8080/DemoServer/demoservelet?value=%d", 20));

POST-style passing has to abide by the HTTP protocol, which is fairly similar to what you're using so far, save for the fact that all parameters must have a trailing newline character. Using your example:

BufferedWriter out = new BufferedWriter(new OutputStreamWriter(conn.getOutputStream()));

out.writeln("message=20");

You could also use a PrintStream, which would make formatting your parameters a little easier to handle if you need to change them:

PrintStream out = new PrintStream(conn.getOutputStream());

out.printf("message=%d\n", 20);

Whether you use GET-style or PUSH-style is up to you, though it depends on the type of data you're passing along.

Answer 2

you must to check if name is a valid numbre. name.match("^-?\\d+$"); it returns true if it is a number

Answer 3

我相信您必须将参数写为参数才能被检测为一个。

out.write("<param name=\"message\" value=\"20\">");

Answer 4

您具有输出名称的值，在调试检查值时确定名称是一个数字。