How to add multiple jar files in classpath in linux

Question

Okay  I m very new to linux and command line  and fairly new to java  I got an internship building a java program  I finally got it done on my machine  windows  and now I have to migrate it to a linux machine to test and then have it run as an executable  I have done much reading and researching on linux and understanding classpaths but it is still all very hard to fully comprehend  It s just not clicking for me yet  Can anyone explain the purpose of classpath in a simplified way using examples  One of the most confusing aspects to me is actually defining the physical path to the jar  Do I start all the way from usr or do I only need to begin from the jvm folder  If it matters  my java program is not located in the jvm folder  Can anyone shed some light for me   EDIT  thank you guys very much for your help  I can t say that I m fully in the clear but my understanding of my situation is a lot better

User · Accepted Answer

You use the -classpath argument  You can use either a relative or absolute path  What that means is you can use a path relative to your current directory  OR you can use an absolute path that starts at the root     Example   bash  java -classpath path to jar file MyMainClass   In this example the main function is located in MyMainClass and would be included somewhere in the jar file   For compiling you need to use javac  Example   bash  javac -classpath path to jar file MyMainClass java   You can also specify the classpath via the environment variable  follow this example   bash  export CLASSPATH  path to jar file path tojar file2  bash  javac MyMainClass java   For any normally complex java project you should look for the ant script named build xml

User · Answer

Say you have multiple jar files a jar b jar and c jar  To add them to classpath while compiling you need to do   javac -cp   a jar b jar c jar HelloWorld java   To run do   java -cp   a jar b jar c jar HelloWorld

User · Answer

The classpath is the place s  where the java compiler  command  javac  and the JVM  command java  look in order to find classes which your application reference   What does it mean for an application to reference another class   In simple words it means to use that class somewhere in its code    Example   public class MyClass      private AnotherClass referenceToAnotherClass                When you try to compile this  javac  the compiler will need the AnotherClass class  The same when you try to run your application  the JVM will need the AnotherClass class  In order to to find this class the javac and the JVM look in a particular  set of  place s   Those places are specified by the classpath which on linux is a colon separated list of directories  directories where the javac JVM should look in order to locate the AnotherClass when they need it     So in order to compile your class and then to run it  you should make sure that the classpath contains the directory containing the AnotherClass class  Then you invoke it like this    javac -classpath  dir1 dir2 path to AnotherClass     dirN  MyClass java   to compile it java -classpath  dir1 dir2 path to AnotherClass     dirN  MyClass   to run it   Usually classes come in the form of  bundles  called jar files libraries  In this case you have to make sure that the jar containing the AnotherClass class is on your classpaht   javac -classpath  dir1 dir2 path to jar containing AnotherClass     dirN  MyClass java   to compile it java -classpath    dir1 dir2 path to jar containing AnotherClass     dirN  MyClass   to run it   In the examples above you can see how to compile a class  MyClass java  located in the working directory and then run the compiled class  Note the     at the begining of the classpath which stands for current directory   This directory has to be added to the classpath too  Otherwise  the JVM won t be able to find it   If you have your class in a jar file  as you specified in the question  then you have to make sure that jar is in the classpath too   together with the rest of the needed directories    Example    java -classpath    dir1 dir2 path to jar containing AnotherClass path to MyClass jar    dirN  MyClass   to run it   or more general  assuming some package hierarchy    java -classpath    dir1 dir2 path to jar containing AnotherClass path to MyClass jar    dirN  package subpackage MyClass   to run it   In order to avoid setting the classpath everytime you want to run an application you can define an environment variable called CLASSPATH    In linux  in command prompt    export CLASSPATH  dir1 dir2 path to jar containing AnotherClass     dirN     or edit the    bashrc and add this line somewhere at the end   However  the class path is subject to frequent changes so  you might want to have the classpath set to a core set of dirs  which you need frequently and then extends the classpath each time you need for that session only  Like this    export CLASSPATH  CLASSPATH  new directories according to your current needs

User · Answer

For linux users  you should know the following     CLASSPATH is specifically what Java uses to look through multiple directories to find all the different classes it needs for your script  unless you explicitly tell it otherwise with the -cp override   Using -cp  --classpath  requires that you keep track of all the directories manually and copy-paste that line every time you run the program  not preferable IMO   The colon       character separates the different directories  There is only one  CLASSPATH and it has all the directories in it  So  when you run  export CLASSPATH       you want to include the current value   CLASSPATH  in order to append to it  For example   export CLASSPATH   export CLASSPATH  CLASSPATH  usr share java mysql-connector-java-5 1 12 jar   In the first line above  you start CLASSPATH out with just a simple  dot  which is the path to your current working directory  With that  whenever you run java it will look in the current working directory  the one you re in  for classes  In the second line above   CLASSPATH grabs the value that you previously entered     and appends the path to a mysql dirver  Now  java will look for the driver AND for your classes  echo  CLASSPATH   is super handy  and what it returns should read like a colon-separated list of all the directories you want java looking in for what it needs to run your script  Tomcat does not use CLASSPATH  Read what to do about that here  https   tomcat apache org tomcat-8 0-doc class-loader-howto html

User · Answer

Step 1   vi    bashrc   Step 2  Append this line on the last   export CLASSPATH  CLASSPATH  home abc lib      Assuming the jars are stored in  home abc lib     Step 3    source    bashrc   After these steps direct complile and run your programs e g  javac xyz java

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