We Keep Coding

How make getRequestURI and queryString in jsp

I am using this:
<li ${(requestScope['javax.servlet.forward.request_uri']=='/example') ? "class='active';" : ""}>
And this code activates my link to me but I've written such code to be active: ${(requestScope['javax.servlet.forward.request_uri'] +="?"+ requestScope['javax.servlet.forward.query_string']=='/example/?buy=e') ? "class='active';" : ""}
But I am getting an error.
Can I get your solution suggestions?

Try this below.
String uri = request.getScheme() + "://" +
request.getServerName() +
("http".equals(request.getScheme()) && request.getServerPort() == 80 || "https".equals(request.getScheme()) && request.getServerPort() == 443 ? "" : ":" + request.getServerPort() ) +
request.getRequestURI() +
(request.getQueryString() != null ? "?" + request.getQueryString() : "");
Note:
This snippet above will get the full URI, hiding the port if the default one was used, and not adding the "?" and the query string if the latter was not provided.

Why is my string doesn't accept null?

I need the String receive the null value if it is not found in mapper.getChave is what is returned. What I do? If I only get nullPointerException
for(String chave : linha.keySet()) {
//Processa chave
String novaChave = mapper.getChave(chave.trim());
if (!(novaChave == null || novaChave.isEmpty())) {
//Processa valor
String novoValor = linha.getString(chave);
temp.append(novaChave, novoValor);
}
else {
extras.append(chave, linha.getString(chave));
}
}
Log
java.lang.NullPointerException
at oknok.validacao.readers.PlanilhaReader.processaAtributosPlanilha(PlanilhaReader.java:237)
Line 237 is
String novaChave = mapper.getChave(chave.trim());
**UPDATE: The first time the loop runs, i have a Nullpointer and chave contains a value
System.out.println(chave.isEmpty() + "\t" + chave + "\t" + chave.trim());
Output
false Veículo Veículo

You need to add null check for mapper as well as chave.
if (mapper!= null && chave != null && !"".equals(chave) {
// do something
}
mapper.getChave(chave.trim())
^ ^ possible places for NPE.

Most probably value of chave or mapper would be null and you are calling trim() and .getChave() on them respectively causing nullpointer

You need to check whether chave is null before trimming it or doing anything else (I'm assuming that mapper is pre-initialised and not null, but you should check that too)
e.g.
if (chave != null && !"".equals(chave.trim()) {
// now do something
}
You may find it easier (more intuitive) to use something like Apache Commons StringUtils.isNotBlank(String). See here for the doc.

There is a null string reference in linha.keySet().

Follow code change null string to "" : you can change "" to anything you like
String novaChave = mapper.getChave((chave == null ? "" : chave).trim());

Ternary operator with string concatination causes partial loss of content?

Boolean isValid = true;
String message = "prefix" + isValid != null ? " midfix " : "suffix";
System.out.println(message);
What do you think is the result of this? I'd expect prefix midfix. But actually the result is: midfix!
Is this an error in the java library itself (1.7)? Should I report a bug for this? Or does this work as intended, and I'm misusing it?
It can be "fixed" using:
String message = "prefix" + (isValid != null ? " midfix " : "suffix");
but anyways shouldn't it work without the brakets?

It is evaluated as :
String message = (("prefix" + isValid) != null) ? " midfix " : "suffix";
which is equivalent to :
String message = ("prefixtrue" != null) ? " midfix " : "suffix";
Therefore "midfix" is returned.
If you wish "prefix midfix" to be returned use parentheses:
String message = "prefix" + (isValid != null ? " midfix " : "suffix");

Ternary operator for strings - any nicer way?

I'm concerned about this construct:
String out = "Text " + (obj==null ? "" : obj.getStr()+" ") + "text continues.";
It works and all, but I think it's ugly. Maybe I'm just too picky..
Anyway, I'm asking, is there some nicer way to do this kind of stuff?Or is this the generally accepted technique?

Use a StringBuilder:
final StringBuilder sb = new StringBuilder("Text ");
if (obj != null)
sb.append(obj.getStr()).append(' ');
final String out = sb.append("text continues.").toString();
Also, why .getStr()? Doesn't obj implement .toString()?
Note that if obj did implement .toString(), you could do "better" than that using Guava's Joiner:
private static final Joiner JOINER = Joiner.on(" ").skipNulls();
//
final String out = JOINER.join("Text", obj, "text continues.");
Ultimately, though, that is a question of style.

Well you can separate out the logic from the format, to start with:
String out = String.format("Text %stextcontinues",
obj == null ? "" : obj.getStr() + " ");

I like it better because it is concise.
The other way is the plain old if-then-else:
String toAdd = "";
if(object != null) {
obj.getStr() + " ";
}
String out = "Text " + toAdd + "text continues.";

String out = "Text text continues.";
if (obj != null)
out = "Text " + obj.getStr() + " text continues.";

printing statement with operator ? : causes unexpected output

I had to create an output depending on an boolean state like
String smily = null;
StringBuffer buff = new StringBuffer();
buff.append(", " + smily == null ? ":)" : ":("); //$NON-NLS-1$
System.out.println(buff.toString());
The problem is the String creation statement
", " + smily == null ? ":)" : ":("
I tested it in 2 different eclipse environments (and may be also 2 diofferent java version, this i did not checked) and the result was different.
Result 1:
:(
Result 2:
false:(
Of course, if i added brackets it is working
buff.append(", " + (smily == null ? ":)" : ":(")); //$NON-NLS-1$
Expected Result:
, :)
Can please somebody explain to me, why java interprets the statement that way?
Thanks

If you check the operator precedence (see this tutorial), then you will notice that addition (+) comes before equality (==). In other words, Java will first evaluate ", " + smily => ", null" before evaluating equality, therefor ", " + smily == null evaluates to false, and so the ternary operator evaluates to ":(".
BTW: You could have avoided this by not concatenating strings before adding them to the StringBuffer (the whole point of a StringBuffer is to make concatenation cheaper):
String smily = null;
StringBuffer buff = new StringBuffer();
buff.append(", ");
buff.append(smily == null ? ":)" : ":(");

the expression ", " + smily == null ? ":)" : ":(" is evaluated as (", " + smily) == null ? ":)" : ":("
This explains your result 1. To be honest, I don't know why result 2 was possible.

StringBuffer.append() takes a String parameter. So when you put this without brackets
buff.append(", " + smily == null ? ":)" : ":(")
at the time of evaluation will be ", " + null. So when the evaluation happens it is always false.
As for why the same code returned two results I can only assume that two different Java versions were used and they handled this situation differently.

String smily = null;
StringBuffer buff = new StringBuffer();
if(smily == null){
buff.append(", " + ":)") ; //$NON-NLS-1$
}else{
buff.append(", " + ":(") ; //$NON-NLS-1$
}

Try this.....................
buff.append(", " + smily == null ? ":)" : ":(");
- In the above statement you are Not mentioning the smily == null ? ":)" : ":(" to be evaluated in the proper way it has to be.
- To solve this you have to use BODMAS rule, the below are always evaluated in the way it has been listed from Left to Right.
Bracket
Power
Division and Multiplication
Addition and Substraction
- Use Bracket to enclose the smily == null ? ":)" : ":("
Eg:
public class Test {
public static void main(String[] args){
String smily = null;
StringBuffer buff = new StringBuffer();
buff.append(", " + (smily == null ? ":)" : ":(")); //$NON-NLS-1$
System.out.println(buff.toString());
}
}
Output: , :)