If you have tried creating JAR file and running Java program form command
line you may have encountered "Failed to load Main-Class
manifest attribute from jar" , This error which haunts many Java
programmer when they enter into command line arena and tries to create JAR file in command line
or IDE like Netbeans and Eclipse. Major problem with "Failed
to load Main-Class manifest attribute from jar" error is
that, it’s unnecessary creates panic which it doesn't deserve, may be because
process involves of creating and running JAR is not that common like running Java
program using "java" command. Anyway in this Java
tutorial we will see Why "Failed
to load Main-Class manifest attribute from jar" comes and
How to fix Failed to load Main-Class manifest attribute from jar error.
Cause of Failed to load Main-Class manifest
attribute from jar in Java
As I have said previously, in order to troubleshoot any error first lookat the error message, many times it provides important clue though I agree some
time it also confuse or mislead mainly in case of those NoClassDefFoundError and ClassNotFoundException. Here
error message is relevant and clear "Failed to load Main-Class
manifest attribute from jar" is saying that java command failed to load "Main-Class" attribute
from Manifest of JAR file, which you are running, it means:
1) Either you have not provided "Main-Class" attribute
in Manifest file
2) You don't have a manifest file in your JAR
3) "Main-Class" attribute is not spelled
correctly
"Main-Class" attribute in MANIFEST.MF file
specify program entry point or name of Main class, a class which contains main method in Java. Main
method is required to run Java program. If your jar's MANIFEST file
doesn't contain "Main-Class" than you can not run Java program using command
"java -jar name.jar" , it will result in "Failed
to load Main-Class manifest attribute from jar". In next
section we will see step by step example of how to reproduce this error and
than how to fix Failed to load Main-Class manifest attribute from jar.
Example
of "Failed to load Main-Class manifest attribute from jar":
In order to create a JAR file from command prompt you need a MANIFEST.MF file which
must follow rules specified for manifest here http://docs.oracle.com/javase/tutorial/deployment/jar/appman.html
. One of the important rule is "Manifest file must end with new line or
carriage return character". Once you have your manifest file ready, you
are ready to create JAR file. In this example we will first create a JAR file whose
MANIFEST file doesn't contain Main-Class attribute
and then will see how it runs.
here is our MANIFEST.MF file:
user@Machine:~/java cat
MANIFEST.MF
Manifest-version: 1.0
There is no Main-class attribute and here is command to create JAR with
Manifest file:
user@Machine:~/java jar
-cvfm test.jar MANIFEST.MF HelloWorld.class
-c for create
-v for verbose
-f for files
-m for manifest
Above command will create a JAR file named test.jar with
MANIFEST file specified after test.jar and include HelloWorld.class from same
directory.
When you run this JAR using java command
you will get Failed to load Main-Class manifest attribute from
jar because our Manifest file doesn't contain "Main-Class" entry:
user@Machine:~/java java -jar test.jar
Failed to load
Main-Class manifest attribute from test.jar
Java will also throw Failed
to load Main-Class manifest attribute from test.jar even if you have Main-Class attribute
but not spelled correctly so watch out for spelling mistake there.
How to fix Failed to
load Main-Class manifest attribute from jar
Now we know what is causing this error, we can fix it by introducing
"Main-Class" attribute in manifest file or correcting it in case
of any spelling mistake on "Main-Class". Also
remember space between attribute and its
value after colon e.g. "Main-Class:HelloWorld" will not
work instead it will throw IOException while creating JAR file as shown
here:
user@Machine:~/java cat MANIFEST.MF
Manifest-version:
1.0
Main-Class:HelloWorld
user@Machine:~/java jar -cvfm test.jar MANIFEST.MF HelloWorld.class
java.io.IOException:
invalid header field
at java.util.jar.Attributes.read(Attributes.java:393)
at
java.util.jar.Manifest.read(Manifest.java:182)
at java.util.jar.Manifest.
at
sun.tools.jar.Main.run(Main.java:151)
at
sun.tools.jar.Main.main(Main.java:1149)
Once you have correct MANIFEST.MF just
repeat the process of creating JAR and running it. This
time it should not throw any Error. Here is command examples of running Java
program from JAR file :
user@Machine:~/java cat
MANIFEST.MF
Manifest-version:
1.0
Main-Class:
HelloWorld
user@Machine:~/java jar -cvfm test.jar MANIFEST.MF HelloWorld.class
added manifest
adding:
HelloWorld.class(in = 450) (out= 311)(deflated 30%)
user@Machine:~/java java -jar test.jar
Executing Java
Program from JAR file
This was the way to fix Failed to load Main-Class manifest
attribute from jar error, when you are creating JAR file from command prompt
but if you are creating JAR from Eclipse or Netbeans IDE, than you need to
follow IDE specific steps. Thankfully both IDE ask you to choose Main Class
while creating JAR.
That's all on How to fix "Failed to load Main-Class
manifest attribute from jar". We have seen what can cause
"Failed to load Main-Class manifest attribute from jar" error and how
we can correct it. let me know if you have seen this error due to any other
reason than incorrect "Main-class" attribute
entry in manifest file.
Other Java debugging tutorials from Javarevisited Blog
Source:http://javarevisited.blogspot.com/2013/01/how-to-fix-failed-to-load-main-class-manifest-attribute-jar-java-eclipse.html
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