classpath - running a java program from the command line

Question

My code compiled fine with the following command:

javac -cp "../lib/*" AvroReader.java

(lib is where i put my jar files)

At run time I get a ClassNotFoundException on the following line:

DatumReader<?> dtmrdr = new GenericDatumReader();

It says it can't find org.apache.avro.generic.GenericDatumReader even though I've imported it.

Why is this happening?

How are you running the program? You have to provide the classpath with all your dependencies when you run your application as well. — wkl
– wkl, Commented Jul 13, 2012 at 0:03
I ran it by running java Generator . Generator is a class that calls a method in AvroReader.java — Dao Lam
– Dao Lam, Commented Jul 13, 2012 at 0:19

duffymo · Accepted Answer · 2012-07-13 00:24:13Z

15

Importing has nothing to do with loading classes or setting CLASSPATH.

Try this:

java -cp .;../lib/* Generator

Using the dot '.' as the first entry in the CLASSPATH assumes that the Generator.class file exists in the directory from which you're running java, and /lib is one level up from that directory. Adjust as needed if both of these are not correct.

answered Jul 13, 2012 at 0:24

duffymo

310k46 gold badges376 silver badges570 bronze badges

Sign up to request clarification or add additional context in comments.

7 Comments

Dao Lam Over a year ago

I'm not sure I understand what you mean by "using . as the first entry in the CLASSPATH"

duffymo Over a year ago

Look very carefully at the compilation string I posted. See the dot just before the semi-colon? That's the step you missed that caused the JVM to not be able to find your Generator.class.

jahroy Over a year ago

@DaoLam - The argument after -cp is the classpath. It is a list of directories separated by ; characters. The first item is . which means the current directory. The second item is ../lib/* which means everything in the ../lib directory. Duffymo is telling you that you need to include the current directory (the location of Generator.class) to your classpath.

Dao Lam Over a year ago

@duffymo: you don't have to be so harsh & discouraging. The fact that I'm here shows that I'm not a pro at Java yet and I'm still learning. After reading jahroy's comment, I realized what it means and I already know it from before. My brain was probably just dead at the time I posted that comment.

Net Dawg Over a year ago

On Mac OS the file separator is colon(:) and need to enclose directories in quotes. So do java -cp .:"../lib/*" Generator

|

Razvan · Accepted Answer · 2012-07-13 00:49:25Z

8

You should run the program including again the same cp:

java -cp "lib directory where i put all the jars" MainClassOfYourApplication

After you compiled it with:

javac -cp "lib directory where i put all the jars" AvroReader.java

More applied to your example:

First step(compile all the needed java files): javac -cp "path/to/jars/*" AvroReader.java //here you should include all the java files not yet compiled but which you need to run your app
Second step: java -cp "path/to/jars/*" package.subpackage1.subpackage2.Generator

edited Jul 13, 2012 at 0:49

answered Jul 13, 2012 at 0:06

Razvan

10.2k6 gold badges41 silver badges51 bronze badges

6 Comments

Dave Newton Over a year ago

You can't just use a directory of jars; you'd need a wildcard. A directory classpath entry is only for class files, AFAIK--a pointer to docs stating otherwise would be helpful. I'm looking at the 1.7 classpath docs.

Dao Lam Over a year ago

I'm calling a method from AvroReader in another class. This is how I ran it: javac -cp "jar directory" AvroReader.java javac Generator.java java Generator I tried what you suggested java -cp "jar directory" Generator, but now it's saying that it can't find Generator.

Dao Lam Over a year ago

@Dave Newton: Yea I actually have a wildcard. It's basically something like "../lib/*" Sorry I wasn't being clear in my original post.

jahroy Over a year ago

@DaoLam - If you're just calling java Generator it won't work because you're not specifying a classpath. Your comment seems to contradict the info in your question, however...

Dao Lam Over a year ago

@jahroy Can you be more specific on how to run it? Thank you! :)

|

desertnaut · Accepted Answer · 2021-03-15 01:09:41Z

0

To compile and execute java file on Linux System with external jar files :

javac -cp jar_file1.jar:jar_file2:jar_file3.jar:. java_program_name.java

java -cp new_mail_api.jar:activation.jar:additional.jar:.java_program_name

To compile and execute java file on Windows System with external jar files :

javac -cp jar_file1.jar;jar_file2;jar_file3.jar;. java_program_name.java

java -cp new_mail_api.jar;activation.jar;additional.jar;.java_program_name

In Unix of Linux, Java Classpath contains names of the directory with colon “:” separated, On Windows Java Classpath will be semicolon “;” separated while if you defined java classpath in Manifest file those will be space separated.

For more knowledge about Classpath, visit https://javarevisited.blogspot.com/2011/01/how-classpath-work-in-java.html

edited Mar 15, 2021 at 1:09

desertnaut

60.8k32 gold badges155 silver badges183 bronze badges

answered Aug 21, 2020 at 8:04

Sumit

6447 silver badges15 bronze badges

Collectives™ on Stack Overflow

classpath - running a java program from the command line

3 Answers 3

7 Comments

6 Comments

Comments

Your Answer

Linked

Hot Network Questions

Collectives™ on Stack Overflow

3 Answers 3

7 Comments

6 Comments

Comments

Your Answer

Sign up or log in

Post as a guest

Linked

Related