StringBuilder append content to a new line every time

Question

I am building a validation routine that validates contents and then gives warning (for failures) in form of StringBuilder. Say in below code I am checking lower bound for values paramX and paramY.

 StringBuilder sb= new StringBuilder();

        if(paramX<10){
            sb.append("paramX cannot be less than 10 ");
        }

        if(paramY<20){
            sb.append("paramY cannot be less than 20 ");
        }

        System.out.println(sb);

It gives output as: paramX cannot be less than 10 paramY cannot be less than 20

but i want output such that, each appended String will be printed on new line. Like below.

paramX cannot be less than 10 

paramY cannot be less than 20

I used following workarounds, but ended up repeating same code again and again(Which i don't want to).

sb.append(System.getProperty("line.separator")); // Add Explicit line separator each time
sb.append("\n");
sb.append("paramX cannot be less than 10 \n");

Is there a simpler way to do it?

Answer 1

Just thought of sharing the new feature of jdk 8 i used for achieving same result. Using StringJoiner we can construct a sequence of characters separated by a delimiter.

StringJoiner formattedString= new StringJoiner("\n"); 
formattedString.add("XXX");
formattedString.add("YYY");
System.out.println(formattedString);  

Answer 2

If you don't want to do it over and over then write a helper method:

public void appendString(StringBuilder builder, String value) {
    builder.append(value + System.lineSeparator());
}

Then call:

if(paramX<10){
    appendString(sb, "paramX cannot be less than 10 ");
}

This way you only have a single place to maintain if you need to change the output format for the errors.

Answer 3

Another option is to use Apache Commons StrBuilder, which has the functionality that you're looking for.

StrBuilder.appendLn()

Answer 4

The simple way would be to keep a list of errors rather than concatenating them as you go. That would help to maintain a separation of concerns between the logical errors and their presentation.

See how Spring validation works: you have an Errors object that keeps a list of errors, and a separate message source object that fills in the user-visible messages for the different errors.

Answer 5

You could try using a PrintStream as it has an println(String string) method which add the new line automatically.

Something like this.

ByteArrayOutputStream bos = new ByteArrayOutputStream();
PrintStream ps = new PrintStream(bos);
ps.println("Line 1");
ps.println("Line 2");
ps.flush();
String message = new String(bos.toByteArray());
System.out.println(message);

Answer 6

First of all you need to include the newline character(\n) at the end of every .append() yourself:

sb.append("paramX cannot be less than 10 \n");

As for repeating you new-line logic just wrap it in a method:

public void append(StringBuilder sb, Object value) {
    sb.append(value).append(System.getProperty("line.separator")).append('\n');
}

And use it like:

if(paramX < 10){
    append(sb, "paramX cannot be less than 10");
}

Answer 7

simply append directly...

        if(paramX<10){
            sb.append("paramX cannot be less than 10 \n ");
        }

        if(paramY<20){
            sb.append("paramY cannot be less than 20 \n ");
        }

Answer 8

Just use \n - it will work everywhere. Also, it looks like you want to conditionally add a line feed if there are two messages:

StringBuilder sb = new StringBuilder();

if (paramX<10) {
    sb.append("paramX cannot be less than 10 ");
}

if (paramY<20) {
    if (!sb.length() > 0) // only add newline if needed
        sb.append('\n');
    sb.append("paramY cannot be less than 20 ");
}