I have created a simple Java program (1 java file that contains the main() ), and I've included all Jar files in the same directory as the .class file. It is giving the NoClassDefFoundError message.
I've tried updating the Classpath to point to the directory, and I've also set "-cp ." to suggest that it look in the same directory as the .class file. However, the program still says it can't find the class def.
Any thoughts on what I should do?
Adding a folder tells java to look in that folder for .class files.
You can't reference .jar files via a folder name... Each .jar file's path must be listed on the CLASS_PATH explicitly.
this question's answer may be useful
When you try running a class from command line then a NoClassDefFound exception usualy means there is something wrong with your classpath.
You have explicitly define the classpath. You can do this in a few ways but the following way is the least prone to error:
Open a command shell and do the following:
1.) set classpath = {path to class files};{path to jars}
2.) java com.example.mainclass
Note: Even if your classes path and jar path is the same you need to specify them explicitly.
Note: If you have more then one jars place them in a folder say lib and add it to the classpath like: {path}/lib/* This will include all of the jar otherwise you have to specify them individually.
References: https://javarevisited.blogspot.com/2011/01/how-classpath-work-in-java.html
Import the following package:
Import java.lang.NoClassDefFoundError;
Related
I have just shifted back from an IDE to Notepad to write a Java program. The program is using 20 JARs. I compiled successfully. When I decided to run the Java class file using
java -cp ".\\*" MyProgram
it was giving the standard error "Couldn't find or load main class....".
I was confused because when I used to run the java command with all files in an existing folder, it would just get those JARs as the current folder is already in the classpath. As the program is running from the current folder, I tried using -cp "." to include it explicitly in the classpath but that didn't work either.
Finally I was able to run the program with this command:
java -cp ".\\*;." MyProgram.java
I am asking this question to understand the actual logic behind Java's classpath.
Correct me if I am wrong, but I think that the JAR is just a standard archive in which all the packages are encapsulated in respective folders. If all the JARs are in my current folder including my main class file then why can't I run it with:
java -cp "." MyProgram
or simply:
java MyProgram
If the problem is with the multiple JAR files to include and that's why we used ".\\*" to include all the JARs in the classpath, then why do we have to explicitly include the current folder again in the classpath using:
java ".\\*;." MyProgram
To include all jar required to run your program in command prompt use wildcard *:
java -classpath E:\lib\* HelloWorld
You are using "." that defines current directory and "./*" defines all files in current directory.
The class path is a list of jar files and directories containing the classes and resources of your program. Mentioning a jar file adds its contents to the class path.
"./*" will get you only the jar files in the current directory, "." adds the current directory to the class path. This allows to access all classes (and the jar files as raw file resources but not its contents, i.e. the classes contained in them).
If you need both in the class path, you have to specify both.
You've answered your own question, sort of.
. means that it will look for .class files in the current directory.
JARs act just like a directory. So to have the abc.jar "directory" you would specify abc.jar in your classpath.
If you need both the .class files present in the current directory, and the .class files packaged into JARs found in the current directory, you would have the following classpath: -cp ".:*.jar
All the answers here are telling you to use the wildcard without extension (* or ./*) but this is a bad practice, you don't want Java to go look into irrelevant files, so specify the extension: *.jar.
"." means current directory not files in the directory
"./*" means all files in current directory.
So you want to use all jars in current directory so 2nd will work
I have some classes in Eclipse which cannot be resolved to a type. I know that classes can be in .class, .jar, .par, .zip files. Are there any other file types that I have to look for? Or is there anything eclipse how I could make Eclipse recognize the classes?
In my general understanding, once I have found these files and added them to the classpath, the Eclipse should be able to recognize them.
Actually my colleague gave me an answer:
If the class cannot be found or resolved to a type within Eclipse, this is only the problem with build path. And to the build path, the files should be added of type as I have said: class, jar, par, zip; no other suffix is accepted.
Maybe I am misunderstanding your question, so please excuse me if I am. Type resolution errors are often due to incorrect imports or misspellings. Ill give an example:
public class Foo extends Component{
//If you forgot to import java.awt.*; You would receive the error
"Component cannot be resolved to a type"
}
Also if you misspelled an extension you would get the same error.When you create a class in eclipse you need to create a new file for that class.
You should also post your code so we know exactly what you're talking about. I don't think your error has anything to do with the classpath. :)
Class path entry could be jar, zip or directory (source)
set CLASSPATH=classpath1;classpath2...
Class paths to the .jar, .zip or .class files. Each classpath should end with a filename or directory depending on what you are setting the class path to:
For a .jar or .zip file that contains .class files, the class path ends with the name of the .zip or .jar file.
For .class files in an unnamed package, the class path ends with the directory that contains the .class files.
For .class files in a named package, the class path ends with the directory that contains the "root" package (the first package in the full package name).
Multiple path entries are separated by semi-colons. With the set command, it's important to omit spaces from around the equals sign (=).
The default class path is the current directory. Setting the CLASSPATH variable or using the -classpath command-line option overrides that default, so if you want to include the current directory in the search path, you must include "." in the new settings.
Classpath entries that are neither directories nor archives (.zip or .jar files) nor * are ignored.
Under Linux I am trying to run a jar file as follows:
java -jar plantuml.jar -testdot
while having CLASSPATH set to any of the following (the file is located at /home/user/plantuml.jar):
export CLASSPATH=/home/user
export CLASSPATH=/home/user/
export CLASSPATH=/home/user/plantuml.jar
In either case, no matter how I define CLASSPATH, the java command gives an error Unable to access jarfile plantuml.jar. What am I doing wrong here?
You have to supply the complete path after the parameter -jar. So for your example you have to call
java -jar /home/user/plantuml.jar -testdot
The $CLASSPATH is only evaluated to find additional files (classes/resources) but not the jar file defined in the command line.
export CLASSPATH="/path/to/class_or_jar1":"/path/to/class_or_jar2":"${CLASSPATH}"
Maybe you are missing name of the main class or path to the jar. Have you tried execute it:
java -jar full_path/plantuml.jar package.YourClass -testdot
Is your program depending on other classes? If yes you might want to add -cp parameter.
The classpath is used to find classes when you refer to them by name. It's essentially a list of paths (directories AND jar/zip files) where the JVM needs to look for classes, or other resources when using methods like ClassLoader.getResourceAsStream().
The value passed to the -jar option on the command line is the file-path to the JAR file.
So, it won't find a jar file if you are only referring to the jar file by name. The JAR file path in the CLASSPATH is supposed to be a path element that 'contains' other resources.
What you need to do here, is either
Provide the full path to the jar file when trying to execute the jar
Set the classpath to the jar file's path, and run the java command giving the name of the main class you want to execute.
my program is in C:\Users\Programs\x.java
X.java is using some files that are in y.jar, z.jar.
y.jar and z.jar are in C:\Users\Programs folder.
(1)
C:Users\Programs> javac x.java
(2)
C:Users\Programs> javac -classpath y.jar:z.jar x.java
I am not getting any errors when I do (2) but when I do (1) I am getting errors. Isn't that classpath is set to current folder. If so why is it not seeing y.jar and z.jar.
Contents of a jar residing on the classpath are not automatically added to the classpath itself. A proper classpath in your case would be what you specified in case (2).
The classpath includes the current folder.
However, it does not include subfolders of the current folder.
If you try to use com.example.MyClass, Java will look for a file named com/example/MyClass.class directly inside of each folder in the classpath.
It does not look in subfolders or JARs inside of folders in the classpath.
Yes, classpath should indeed be set to the current folder by default. However, setting it to a given folder is not the same as setting it to a specific JAR file.
I have a program attempting to use classes from the jakarta-poi-3.0.2.jar in my /usr/share/java directory:
import org.apache.poi.hssf.usermodel.HSSFCell;
import org.apache.poi.hssf.usermodel.HSSFCellStyle;
import org.apache.poi.hssf.usermodel.HSSFWorkbook;
etc...
When I compile, I get a package org.apache.poi.hssf.usermodel does not exist error for each of the imports above.
I have /usr/share/java on my classpath. Am I missing anything else?
/usr/share/java on the classpath does not bring in all jars in /usr/share/java.
Try putting /usr/share/java/jakarta-poi-3.0.2.jar in your classpath instead.
First up, you might want to upgrade - Apache POI 3.0.2 is over 3 years old, and there have been a lot of fixes since then!
As for your issue, you either need to list each jar file individually on your classpath, or you need to place all your jars into the jre lib directory (the contents is which is automatically included). The latter isn't generally recommended though...
You can't just list a directory on the classpath, and have the jars from within it picked up, sorry. Only individual class files will be loaded from a classpath directory, jars won't be
Bootstrap classpath is $JAVA_HOME/lib
but for user applications use user classpaths setting -classpath parameter like that:
java -classpath /usr/share/java/myclasses.jar
The following solution helped me
The class path is the path that the Java runtime environment searches for classes and other resource files. The class search path (more commonly known by the shorter name, "class path") can be set using either the -classpath option when calling a JDK tool (the preferred method) or by setting the CLASSPATH environment variable. The -classpath option is preferred because you can set it individually for each application without affecting other applications and without other applications modifying its value.
C:> sdkTool -classpath classpath1;classpath2...
-or-
C:> set CLASSPATH=classpath1;classpath2...
where:
sdkTool
A command-line tool, such as java, javac, javadoc, or apt. For a listing, see JDK Tools.
classpath1;classpath2 Class paths to the .jar, .zip or .class files. Each classpath should end with a filename or directory depending on what you are setting the class path to:
For a .jar or .zip file that contains .class files, the class path ends with the name of the .zip or .jar file.
For .class files in an unnamed package, the class path ends with the directory that contains the .class files.
For .class files in a named package, the class path ends with the directory that contains the "root" package (the first package in the full package name).
Multiple path entries are separated by semi-colons. With the set command, it's important to omit spaces from around the equals sign (=).
The default class path is the current directory. Setting the CLASSPATH variable or using the -classpath command-line option overrides that default, so if you want to include the current directory in the search path, you must include "." in the new settings.
Classpath entries that are neither directories nor archives (.zip or .jar files) nor * are ignored.
Reference :http://download.oracle.com/javase/6/docs/technotes/tools/windows/classpath.html