After a search in LDAP, written in Java, I have a valid entry as
cn=DE9-M5T,ou=students,ou=users,o=data
When I now do
if (entry != null && entry.getAttribute("modifyTimestamp") != null) {
String dn = entry.getDN();
String modifyTimestamp = entry.getAttribute("modifyTimestamp").getStringValue();
String oldTimestamp = modificationTimestampCache.get(dn);
String cnUserId = entry.getAttribute("cn").getStringValue();
...
}
the last line gives a NullPointerException, which means that
entry.getAttribute("cn")
must return null. Following the documentation, this would only happen if the given attribute (here "cn") could not be found as exact match. Is there any reason that this could happen for "cn" in LDAP?
From your code I can't figure out the exact types of your entry and its getAttribute(), but consider this:
cn is a multivalued ldap attribute, where modifytimestamp is single valued.
So, the values of cn are probably stored in an array-like structure, I guess that your getAttribute() does not handle this as you expect.
Not every object class has a cn attribute. Only those where it appears in the schema.
Evidently this isn't one of them.
Related
I'm working with on a Java program that checks a config file integrity.
On some point, I need to ensure that some mandatory values are setted up, either give it a default value.
So, I made a HashTable<String, String> working like a key => value table. On this table I store all the configuration lines on the file, and then I check it.
The problem comes when a specific value does not exist, for example:
String p = null;
/*...*/
//here I'm trying to get the LOG value
p = this.PAIRS.get("LOG");
if(p.equals(null) || p.equals("")){
//set default value
}
The problem is that I'm getting a NullPointerException, so it would be fine if someone can help me on how to determinate if this.PAIRS.get("LOG"); found a key or not...
Thanks!
EDIT: Solved, the right thing was using == and not an equals.
Thanks again!
If p is null, a NullPointerException will be thrown because it is not an instance of an Object (so the equals method doesn't exist). Checking for null should be done the following way : p == null
p = this.PAIRS.get("LOG");
This code return null if the key is not present and when you are doing below statement it will throw exception
if(p.equals(null) || p.equals("")){
//set default value
}
Instead check null first then do .equals
if(p==null || p.equals("")){
//set default value
}
I saw a lot of SO posts saying that Java set any uninitialized variable to null (like here, here or here...).
But lately, I went upon this code, written by Google here :
cur = cr.query(builder.build(), INSTANCE_PROJECTION, selection, selectionArgs, null);
while (cur.moveToNext()) {
String title = null;
long eventID = 0;
long beginVal = 0;
// Get the field values
eventID = cur.getLong(PROJECTION_ID_INDEX);
beginVal = cur.getLong(PROJECTION_BEGIN_INDEX);
title = cur.getString(PROJECTION_TITLE_INDEX);
// Do something with the values.
...
}
I would genuinely rather do this :
// Get the field values
long eventID = cur.getLong(PROJECTION_ID_INDEX);
long beginVal = cur.getLong(PROJECTION_BEGIN_INDEX);
String title = cur.getString(PROJECTION_TITLE_INDEX);
I assume Google developpers are somehow really qualified, so I wonder, since we are in the very same scope : what are the pros and cons of declaring the first way instead of the second ?
It's a question of style. I don't initialise unnecessarily for two reasons:
Doing so clobbers an extra check a Java compiler will give you as compilation will not be successful if a variable that is not initialised on all control paths is encountered.
It gives the impression that null is an acceptable value for the reference, which often it isn't.
I'm to trying to make an android app where I accept input from the user using the speech Recognition server. I'm capturing the results in a ArrayList as follows :
matches = data.getStringArrayListExtra(
RecognizerIntent.EXTRA_RESULTS);
matches is declared globally as :
ArrayList<string> matches;
Now I want to check if the user has spoken a particular word. So I do this :
if(matches.contains("TextToBeDetected")) { }
But the line above throws a NullPointerException.
Please help.
P.S Yes, I'm a Java and Android newbie.
Obviously, your matches is null. As per the Intent documentation, http://developer.android.com/reference/android/content/Intent.html#getStringArrayListExtra%28java.lang.String%29
getStringArrayListExtra returns null if the key is not found in the bundle.
Test for nullity before testing if it contains anything
It sounds as though getStringArrayListExtra is returning null (the docs say it will if there is such ArrayList value found), and so when you try matches.contains("TextToBeDetected") it fails because you're trying to dereference a null reference. You'll want to check the return value from getStringArrayListExtra to make sure it's not null before you use it. E.g.:
matches = data.getStringArrayListExtra(
RecognizerIntent.EXTRA_RESULTS);
// ...
if (matches != null) {
if (matches.contains("TextToBeDetected")) {
// do something
}
}
If you see the docs Android.Content.Intent.GetStringArrayListExtra It says
the value of an item that previously added with putExtra() or null if no ArrayList value was found.
You need to check for the list being null before setting it to matches.
Are you sure that matches is allocated?
Try this, and look at your logcat output:
if (matches == null) {
Log.d("YourAppName", "matches is null!");
} else if (matches.contains("TextToBeDetected")) {
Log.d("YourAppName", "matches does contain TextToBeDetected");
} else {
Log.d("YourAppName", "matches does not contain TextToBeDetected");
}
data.getStringArrayListExtra(RecognizerIntent.EXTRA_RESULTS)
will return the value of an item that previously added with putExtra() or null if no ArrayList value was found. In your case, maybe it returned null
I'm running a Tomcat WAR, which uses a MySQL database.
The application will run in foreign languages, so I had to change all database character parameters to utf8.
One application string (appPrefix) has to be empty (because the WAR is deployed in the root dir). This worked well, until I created a new database in UTF8 and migrated all the tables.
Now I get a NullPointerException because of the appPrefix being empty:
java.lang.NullPointerException
com.horizon.servlet.PageServlet.doMainPageRequest(PageServlet.java:177)
com.horizon.servlet.PageServlet.doRequest(PageServlet.java:53)
com.horizon.servlet.PageServlet.doGet(PageServlet.java:33)
javax.servlet.http.HttpServlet.service(HttpServlet.java:617)
javax.servlet.http.HttpServlet.service(HttpServlet.java:717)
com.horizon.filters.P3PFilter.doFilter(P3PFilter.java:19)
The above is all the same error causing ripples throughout the application.
It's all caused by appPrefix being empty, but it should..
Should I specify it as empty in another way? Or should I try to hardcode my way around this?
EDIT:
As per the request in the comment below, here is PageServlet.java:177
request.setAttribute("appPrefix", appManager.getAppStringById(11).getValue());
This references AppManager.java:
public static final int APP_STRING_APPLICATION_PREFIX = 11;
which is populated by
public AppString getAppStringById(int id) {
AppString string = (AppString) stringCache.get(id);
if (string == null) {
String query = "SELECT * FROM app_strings WHERE id = ?";
List<Object> params = new LinkedList<Object>();
params.add(id);
string = execQueryLoadSingleRecord(query, params, new LoadAppString());
if (string != null) {
populateCache(stringCache, id, string);
}
}
return string;
}
As per
request.setAttribute("appPrefix", appManager.getAppStringById(11).getValue());
and
The database entry it's getting is empty, as it should.. So shouldn't it return null? Does this conflict with anything? The db string being empty was no problem until I changed the database's encoding to UTF8 from the default latin1 swedish!
I understand that it's not a problem at all if appManager.getAppStringById(11) can possibly return null, right? In that case, you should check for it before calling getValue() on it.
AppString appString = appManager.getAppStringById(11);
if (appString != null) {
request.setAttribute("appPrefix", appString.getValue());
}
As to why it returns null after you changed the table's charset; I have no idea. Perhaps it's just big coincidence or a misinterpretation of the problem. Perhaps you added getValue() call later on because you wanted to use ${appPrefix} instead of ${appPrefix.value} in EL or something. Or perhaps you rewrote execQueryLoadSingleRecord() that it returned null instead of empty string. Or perhaps the column's default value is null instead of an empty string. Or perhaps it's a bug in the JDBC driver used. Who knows. Using null as "no value" is perfectly fine and should be treated as such.
OMG. I have a little project to do and the Strings are killing me!
Now, I have a String which is null (is taken the value from invoking getParameter() from a servlet).
The problem is that, I'm trying to see if it's null, and, even if it's null, in the program is telling me that is not null, but later in program, when I'm using the variable, I receive a exception saying the variable is null.
System.out.println("In " + ID); // in console: In null
if ((ID == null) || (ID == "null") || ID.equals(null) || **ID.equals("null")**)
{
// after I put the 4th condition, the if is working right (WHAT IS THE PROBLEM?)
System.out.println("==null");
this.ID = "";
}
else
{
System.out.println("!=null");
this.ID = ID;
}
System.out.println("After " + ID);
What I'm doing wrong?
Only the forth condition is working! What about the rest(except second one, because that condition i put it because I was desperate)
I taught ID == null or ID.equals(null) will be ok, but no.
Edit:
The problem is that, I'm getting the value of the ID from a form(form 1 let's say- usually). But in this case, I'm using form 2 which doesn't have any ID inputs, so ID must be null and not "null"
ID.equals("null")
Clearly, ID contains the four-letter string "null". So it's not null (the value for "nothing").
See the Java glossary for more on the null constant. Basically a variable has the value null if it does not reference any object. The string "null" is an object however, namely an instance of the class String, and in this case the variable ID references this object.
(Note that by convention Java variables start with a lower case letter, and acronyms like ID are written completely lower case, so write id instead of ID.)
Here are the four tests you've tried. The first and the fourth are the only ones that you should need.
ID == null : is the field 'ID' null?
ID == "null": is the ref for the field 'ID' the same as the newly allocated String "null"? This should generally return false.
ID.equals(null): this should always return false - conceptually were this ever true you should throw a NullPointerException.
ID.equals("null"): is the value of the String 'ID' the same as the value of the String "null"?
Since you get the string from a servlet i can say that this is normal.
Java converts a null string to a "null" string on some conditions.
Obviously the string you retrieve is not a null value, but it is a 4 char string "null"
Why don't you try debugging? Or just see what does this return:
System.out.println("Length of ID: " + ID.Length);
Edit: If you don't get exception here, this means that the string is not null and also output "Length of ID: 4" will mean that the string is really ID = "null"
EDIT2: Alright it seems that some guys do not understand what is going on here and they say how can a null string be "null" in some conditions in Java? They find it riddiculus. I prefer them to try this on java:
String abc = null;
String xyz = "hello";
System.out.println(xyz + abc);
The output will be "hellonull" Nothing else...
Also here we have a servlet. There is a null data. Servlet sends the null data as "null" what should it do? An empty string? Come on!!! "
Looks like it is return the String "null" and not a Null Object.
If the result was actually a null then
ID == null
would suffice, but as is mentioned the string value of ID is obviously "null" rather than the null object.
You should use .equals when comparing strings rather than using ==
This blog explains more about his:
http://blog.enrii.com/2006/03/15/java-string-equality-common-mistake/
So, "null" does not equal null, in Java.
If the value is coming from a Servlet then the container is most likely converting an empty form field to a blank string. You should do a check against null and blank ("").
if (value==null || value.equals(""))
Alternatively you can use String's isEmpty() method:
if (value==null || value.isEmpty())
If the value of your variable ID is the string literal "null", then I would guess that there is a bug earlier in the code when you retrieve it using the getParameter() method. According to the docs, the getParameter() method is supposed to return null (the null reference) if there is no value for the specified name. This indicates that somewhere you are doing an operation that converts the result to the string literal, perhaps concatinating with the empty string (i.e. ID + "" ; )