Java accepts one (1) multiline string from stdin

Question

I am writing a program that can either accepts a ".sql" file or accepts an SQL statement from the stdin. The problem comes form stdin:

Scanner scanner = new Scanner(new BufferedInputStream( System.in));
System.out.println("Enter SQL statements");
StringBuilder stringBuilder = new StringBuilder();
while (scanner.hasNext()) {
    stringBuilder = stringBuilder.append(scanner.nextLine()).append("\n");
}
sqlQuery=stringBuilder.toString();

It is modified from the answer here. But when I enter or paste the statement(s) into the terminal, it does not go to the next step, instead the statement keeps appending "\n". I want the user input to end after they hit enter (similar to this problem but in Java). How do I do it?

So check whether the user entered an empty string? – SLaks Mar 15 '17 at 19:54 — SLaks, Mar 15 '17 at 19:54

score 1 · Answer 1 · answered Mar 15 '17 at 19:59

1

The code you present anticipates that the input will be terminated by the end of the stream with which the Scanner is associated, not by the end of a single line -- see how the scanner.nextLine() invocation is inside a while loop?

If you want to read only one line then get rid of the loop. Moreover, if you're not concatenating multiple lines, then you don't need a StringBuilder either. Be sure that this is what you want, however, for it is relatively common for SQL statements to be written in multiline format.

answered Mar 15 '17 at 19:59

John Bollinger

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Note: text-mode SQL interfaces commonly accept multiline input. They generally look for some sort of delimiter to recognize the end of a query, such as a period or semicolon on a line by itself. – John Bollinger Mar 15 '17 at 20:19
But some sql statements consist of multiple commands, such as multi-table insertion or creating a view and then extracting data from it – Dylan Czenski Mar 15 '17 at 20:23
@DylanChensky, multiple commands are not an issue, as you can just enter them sequentially. Multiline *individual* commands are a different matter, and if you want to support these then you have a fundamental problem: how is the program supposed to recognize a given line as the last in a command, vs. expecting additional lines to follow? I already said a word or two about that in my previous comment. – John Bollinger Mar 15 '17 at 20:35

score 1 · Accepted Answer · answered Mar 15 '17 at 20:22

To collect all the input until a double new-line (a blank line), you can set a custom delimiter on the Scanner, using a regex, and it will collect the input with a single call to scanner.next().

Scanner scanner = new Scanner(System.in);

System.out.println("Enter SQL statements");

scanner.useDelimiter("\n\n"); // an empty line
String sqlQuery = scanner.next();
scanner.reset(); // resets the delimiter

Java accepts one (1) multiline string from stdin

2 Answers2