I'm trying to understand the inclusion of third party jar files in a java project using only the command line in Windows 10.
Specifically, I try to include the file json-20200518.jar in my "project" so that I can use the java object JSONObject in the project.
My java file:
package com.mypackage.example;
import org.json.JSONObject;
class Example {
public static void main(String[] args) {
// ... program logic
}
}
location of my java file (Examp.java):
./com/mypackage/example
location of jar file:
./jars
using cmd win10 I compile:
javac -cp "C:\Users\pfort\Desktop\java\jars\json-20200518.jar" "C:\Users\pfort\Desktop\java\com\mypackage\example\Examp.java"
compilation is successful.
Run:
java -cp "C:\Users\pfort\Desktop\java\jars\json-20200518.jar" com.mypackage.example.Examp
I get a report:
Error: Could not find or load main class com.mypackage.example.Pokus
Caused by: java.lang.ClassNotFoundException: com.mypackage.example.Pokus
Second attempt:
java -cp "C:\Users\pfort\Desktop\java\jars\json-20200518.jar" "C:\Users\pfort\Desktop\java\com\mypackage\example\Pokus"
But the same error message comes back to me.
Where am I going wrong? Is it the wrong structure? I don't get it, the compilation is successful but the run does not work.
The compiled Examp.class file isn't part of json-20200518.jar, so you'll need to add the directory containing it to the command line. Assuming it's the current directory (.):
java -cp "C:\Users\pfort\Desktop\java\jars\json-20200518.jar;." com.mypackage.example.Examp
I have directory /tmp
then I need to execute cd and go to that folder.
Then I need to execute ./executeScript
Preparation
To start solving the problem, I created a directory /home/vulpini99/tmp. In this directory, I created the bash-script test.sh, which will open firefox for us:
firefox
Then I created a java-file named LinuxCommand.java in the directory /home/vulpini99.
Main part
cd is just an internal shell command and not an executable program, so I suggest to just use the full path of the bash-script. So the command we want to execute is
bash /home/vulpini99/tmp/test.sh.
In Java, you can use Runtime for this purpose:
import java.io.IOException;
public class LinuxCommand {
public static void main(String[] args) {
Runtime run = Runtime.getRuntime();
try {
run.exec("bash /home/vulpini99/tmp/test.sh");
}
catch(IOException e) {
e.printStackTrace();
}
}
}
I already install jco3 for linux.
I'm using ubuntu 16.04 x86_64 and java-8-oracle
as the documentation said, i need to add LD_LIBRARY_PATH and CLASSPATH to jco directory.
export LD_LIBRARY_PATH=/home/zain/sapjco
export CLASSPATH=/home/zain/sapjco/sapjco3.jar
then create simple jco connection test
import com.sap.conn.jco.*;
public class testjco {
public static void main(String[] args) {
JCO.Client mConnection;
try {
mConnection = JCO.createClient("301", // SAP client
"somecoolguy", // userid
"****", // password
"EN", // language
"XXX", // application server host name
"00"); // system number
mConnection.connect();
System.out.println(mConnection.getAttributes());
mConnection.disconnect();
} catch (Exception ex) {
ex.printStackTrace();
System.exit(1);
}
}
}
but when i run my project i got error
error: package com.sap.conn.jco does not exist
is there any particular step i missed?
I don't know if you've already done this but:
export LD_LIBRARY_PATH=/home/zain/sapjco
export CLASSPATH=/home/zain/sapjco/sapjco3.jar
only work in the current bash instance, which means that if you ever close that terminal window then that export path will be gone. One way to keep it is to add it to your ~/.profile
then you can just run this source ~/.bashrc in order to refresh your bash window.
Don't know if that helped since I have never coded Java in Ubuntu, only on Mac with Eclipse/Idea. Anyways, if that's not how to do it, then there's a problem with the way you imported your sapjco3.jar to your project.
You also need to use your CLASSPATH environment variable and pass it as classpath argument to your JVM instance that shall run your project.
But I don't think that you are really at the step of running your project, you must be already failing to compile your class testjco. (By the way, I recommend to follow the common Java naming conventions and let all class names start with an uppercase letter.)
You are importing the package com.sap.conn.jco which belongs to the SAP Java Connector 3.0 (sapjco3.jar), but in your code you use the JCo API from package com.sap.mw.jco of the outdated SAP Java Connector 2.0/2.1 (sapjco.jar). That does not work and cannot be compiled.
I have a Baseloader.java class which makes use of Postgresql database, and I have a postgresql42.jar file which handles the jdbc stuff.
Baseloader.java
import java.sql.Connection;
import java.sql.DriverManager;
public class Baseloader
{
public static void main(String[] args)
{
System.out.println("Hello, sir!");
Connection c = null;
try {
Class.forName("org.postgresql.Driver");
c = DriverManager
.getConnection("jdbc:postgresql://localhost:5432/my_base",
"postgres", "123");
System.out.println("Done, sir!");
} catch (Exception e) {
e.printStackTrace();
System.err.println(e.getClass().getName()+": "+e.getMessage());
System.exit(0);
}
System.out.println("Opened database successfully");
}
}
So, when I compile and run this code through Netbeans (the postgresql.jar was included using GUI into Libraries folder) everything goes OK, the output is
Hello, sir!
Done, sir!
Opened database successfully
But when I try to run the compiled class file from cmd I get an error.
I placed Baseloader.class and postgresql42.jar into the same folder and cd'ed into that folder in cmd. Then I use the java -classpath postgresql42.jar Baserunner command which was proposed on one of the answers here, but it gava me Could not find or load main class Baseloader error.
If I type just java Baseloader it gives Exception in thread "main" java.lang.UnsupportedClassVersionError.
What I'm doing wrong and how to fix it?
EDIT: I've changed the java version in cmd: now java -version gives 1.8.0_73'.Then I checked which version Netbeans used: System.out.println(System.getProperty("java.version")) it also gave 1.8.0_73.
In environmental variables the JAVA_HOME is C:\Program Files\Java\jdk1.8.0_73, while System.out.println(System.getProperty("java.home")) gives C:\Program Files\Java\jdk1.8.0_73\jre. Can that difference be the case?
EDIT2: Changed JAVA_HOME to C:\Program Files\Java\jdk1.8.0_73\jre with no result.
Also javac -version gives the same newest 1.8.0_73 now.
This question already has answers here:
What does "Could not find or load main class" mean?
(61 answers)
Closed 7 years ago.
I am having trouble compiling and running my Java code, intended to allow me to interface Java with a shared object for Vensim, a simulation modeling package.
The following code compiles without error:
javac -d . -cp ./apache-log4j-1.2.16/log4j-1.2.16.jar:./vensim.jar SpatialModel.java VensimHelper.java VensimException.java VensimContextRepository.java
However, when I try to run the following:
java -cp ./apache-log4j-1.2.16/log4j-1.2.16.jar:./vensim.jar SpatialModel vars
I get the following error: "Error: Could not find or load main class SpatialModel
". My SpatialModel.java code does contain a 'main' method (below), so I'm not sure what the problem is - can anyone please help me out? Thanks.
import java.io.File;
import java.text.NumberFormat;
import java.util.ArrayList;
import java.util.Arrays;
import java.util.List;
import org.apache.log4j.Logger;
public class SpatialModel {
private VensimHelper vh;
public static final String DLL_LIBNAME_PARAM = "vensim_lib_nam";
public static final String MODEL_PATH_PARAM = "vensim_model_path";
private final static int VENSIM_CONTEXT_CREATION_MAX_FAILURE_COUNT = 10;
public SpatialModel() throws SpatialException {
String libName = System.getProperty(DLL_LIBNAME_PARAM);
String modelPath = System.getProperty(MODEL_PATH_PARAM);
if(libName == null || libName.trim().equals("")) {
log.error("Vensim library name has to be set with -D" + DLL_LIBNAME_PARAM);
throw new SpatialException("Vensim library name has to be set with -D" + DLL_LIBNAME_PARAM);
}
if(modelPath == null || modelPath.trim().equals("")) {
log.error("Model path has to set with -D" + MODEL_PATH_PARAM);
throw new SpatialException("Model path ahs to be set with -D" + MODEL_PATH_PARAM);
}
for (int i = 0; i < VENSIM_CONTEXT_CREATION_MAX_FAILURE_COUNT && vh == null; i++) {
try {
log.info("creating new vensim helper\n\tdll lib: " + libName + "\n\tmodel path: " + modelPath);
vh = new VensimHelper(libName, modelPath);
} catch (Throwable e) {
log.error("An exception was thrown when initializing Vensim, try: " + i, e);
}
}
if (vh == null) {
throw new SpatialException("Can't initialize Vensim");
}
}
public static void main(String[] args) throws VensimException {
long before = System.currentTimeMillis();
String libName = System.getProperty(DLL_LIBNAME_PARAM);
String modelPath = System.getProperty(MODEL_PATH_PARAM);
if (libName == null) {
libName = "libvensim";
}
if(modelPath == null) {
modelPath = "~/BassModel.vmf";
}
System.setProperty(DLL_LIBNAME_PARAM, libName);
System.setProperty(MODEL_PATH_PARAM, modelPath);
if (args.length > 0 && args[0].equals("info")) {
System.out.println(new VensimHelper(libName, modelPath).getVensimInfo());
} else if (args.length > 0 && args[0].equals("vars")) {
VensimHelper helper = new VensimHelper(libName, modelPath);
String[] vars = helper.getVariables();
for (String var : vars) {
System.out.println(helper.getVariableInfo(var));
}
} else {
File f = new File(".");
System.out.println(f.getAbsolutePath());
SpatialModel sm = new SpatialModel();
}
System.out.println("Execution time: " + (System.currentTimeMillis() - before));
}
}
You must ensure that you add the location of your .class file to your classpath. So, if its in the current folder, add . to your classpath.
Note that the Windows classpath separator is a semi-colon, i.e. a ;.
If the class is in a package
package thepackagename;
public class TheClassName {
public static final void main(String[] cmd_lineParams) {
System.out.println("Hello World!");
}
}
Then calling:
java -classpath . TheClassName
results in Error: Could not find or load main class TheClassName. This is because it must be called with its fully-qualified name:
java -classpath . thepackagename.TheClassName
And this thepackagename directory must exist in the classpath. In this example, ., meaning the current directory, is the entirety of classpath. Therefore this particular example must be called from the directory in which thepackagename exists.
To be clear, the name of this class is not TheClassName, It's thepackagename.TheClassName. Attempting to execute TheClassName does not work, because no class having that name exists. Not on the current classpath anyway.
Finally, note that the compiled (.class) version is executed, not the source code (.java) version. Hence “CLASSPATH.”
You can try these two when you are getting the error: 'could not find or load main class'
If your class file is saved in following directory with HelloWorld program name
d:\sample
java -cp d:\sample HelloWorld
java -cp . HelloWorld
I believe you need to add the current directory to the Java classpath
java -cp .:./apache-log4j-1.2.16/log4j-1.2.16.jar:./vensim.jar SpatialModel vars
You have to include classpath to your javac and java commands
javac -cp . PackageName/*.java
java -cp . PackageName/ClassName_Having_main
suppose you have the following
Package Named: com.test
Class Name: Hello (Having main)
file is located inside "src/com/test/Hello.java"
from outside directory:
$ cd src
$ javac -cp . com/test/*.java
$ java -cp . com/test/Hello
In windows the same thing will be working too, I already tried
If you work in Eclipse, just make a cleanup (project\clean.. clean all projects) of the project.
You have to set the classpath if you get the error:
Could not find or load main class XYZ
For example:
E:\>set path="c:\programfiles\Java\jdk1.7.0_17\bin"
E:\>set classpath=%classpath%;.;
E:\>javac XYZ.java
E:\>java XYZ
I got this error because I was trying to run
javac HelloWorld.java && java HelloWorld.class
when I should have removed .class:
javac HelloWorld.java && java HelloWorld
Check your BuildPath, it could be that you are referencing a library that does not exist anymore.
If you're getting this error and you are using Maven to build your Jars, then there is a good chance that you simply do not have your Java classes in src/main/java/.
In my case I created my project in Eclipse which defaults to src (rather than src/main/java/.
So I ended up with something like mypackage.morepackage.myclass and a directory structure looking like src/mypackage/morepackage/myclass, which inherently has nothing wrong. But when you run mvn clean install it will look for src/main/java/mypackage/morepackage/myclass. It will not find the class but it won't error either. So it will successfully build and you when you run your outputted Jar the result is:
Error: Could not find or load main class mypackage.morepackage.myclass
Because it simply never included your class in the packaged Jar.
I know this question was tagged with linux, but on windows, you might need to separate your cp args with a ; instead of a :.
java -cp ./apache-log4j-1.2.16/log4j-1.2.16.jar;./vensim.jar SpatialModel vars
http://docs.oracle.com/javase/7/docs/technotes/tools/windows/classpath.html
If you try to run a java application which needs JDK 1.6 and you are trying to run on JDK 1.4, you will come across this error. In general, trying to run a Java application on old JRE may fail. Try installing new JRE/JDK.
Problem is not about your main function. Check out for
javac -d . -cp ./apache-log4j-1.2.16/log4j-1.2.16.jar:./vensim.jar SpatialModel.java VensimHelper.java VensimException.java VensimContextRepository.java
output and run it.
Project > Clean and then make sure BuildPath > Libraries has the correct Library.
java -verbose:class HelloWorld might help you understand which classes are being loaded.
Also, as mentioned before, remember to call the full qualified name (i.e. include package).
I was using Java 1.8, and this error suddenly occurred when I pressed "Build and clean" in NetBeans. I switched for a brief moment to 1.7 again, clicked OK, re-opened properties and switched back to 1.8, and everything worked perfectly.
I hope I can help someone out with this, as these errors can be quite time-consuming.
This problem occurred for me when I imported an existing project into eclipse. What happens is it copied all the files not in the package, but outside the package. Hence, when I tried run > run configurations, it couldn't find the main method because it was not in the package. All I did was copy the files into the package and Eclipse was then able to detect the main method. So ultimately make sure that Eclipse can find your main method, by making sure that your java files are in the right package.
If so simple than many people think, me included :)
cd to Project Folder/src/package there you should see yourClass.java then run javac yourClass.java which will create yourClass.class then cd out of the src folder and into the build folder there you can run java package.youClass
I am using the Terminal on Mac or you can accomplish the same task using Command Prompt on windows
If you are using Eclipse... I renamed my main class file and got that error. I went to "Run As" configurator and under the class path for that project, it had listed both files in the class path. I removed old class that I renamed and left the class that had the new name and it compiled and ran just fine.
This solved the issue for me today:
cd /path/to/project
cd build
rm -r classes
Then clean&build it and run the individual files you need.
I have a similar problem in Windows, it's related to the classpath. From the command line, navigate until the directory where it's located your Java file (*.java and *.class), then try again with your commands.
I use Anypoint Studio (an Eclipse based IDE). In my case everything worked well, until I found out that while running the java code, something totally different is executed. Then I have deleted the .class files. After this point I got the error message from this question's title. Cleaning the project didn't solve the problem.
After restarting the IDE everything worked well again.