CODEWITHSUNDEEP
javajava-native-interfaceclasspath
krishnakumar
krishnakumar

Reputation: 2287

Javah error while using it in JNI

Command:

javah -jni JavaHowTo

Result:

error: cannot access JavaHowTo 
class file for JavaHowTo not found

javadoc: error - Class JavaHowTo not found.
Error: No classes were specified on the command line.  Try -help.

I have set the class path correctly, but still i am getting this javah error.

Any solution for this will be much helpful.

Upvotes: 44

Views: 53793

Answers (14)

Glen
Glen

Reputation: 22300

Try

javah -jni com.example.JavaHowTo

where com.example is your package.

You also need to run javah from the directory containing com/example/JavaHowTo.class

e.g. if your structure is

/home/user/com/example/JavaHowTo.class

run javah from 

/home/user

Upvotes: 82

Jon Goodwin
Jon Goodwin

Reputation: 9153

How to generate a `JNI Header` file from an `Android class` file using `javah` (`.java` or `.class` BOTH work equally well).

For Eclipse project on Windows:

Goto the directory where the src, bin and jni folders are (so we can use relative paths to src or bin and jni):

    cd C:\Android\workspace5\AndroidImageFilter

I assume `javah` is in your `PATH` (It is in something like : `C:\Program Files\Java\jdk1.7.0_79\bin\javah.exe`):
            javah -classpath c:\Android\sdk\platforms\android-19\android.jar;./src/ -d ./jni cn.Ragnarok.NativeFilterFunc
                             ^                                ^      ^      ^   ^    ^   ^   ^                 ^
                             |                                |      |      |   |    |   |   |                 |
Your android:targetSdkVersion="16"----------------------------+      |      |   |    |   |   |                 |
                             |                                       |      |   |    |   |   |                 |
                             |                                       |      |   |    |   |   |                 |
path to android.jar ---------+---------------------------------------+      |   |    |   |   |                 |
                                                                            |   |    |   |   |                 |
                                                                            |   |    |   |   |                 |
                                                                            |   |    |   |   |                 |
semicolon (;) important ! --------------------------------------------------+   |    |   |   |                 |
                                                                                |    |   |   |                 |
You can use the source directory (yes you can !) (OR the /bin/classes/ dir)-----+    |   |   |                 |
                                                                                     |   |   |                 |
Where to put the output file (cn_Ragnarok_NativeFilterFunc.h in this case)-----------+---+   |                 |
                                                                                             |                 |
The dot (.) spearated full package name path to the .java source file WITH file name --------+                 |
                                                                                                               |
File name of a java class -------------------------------------------------------------------------------------+

For Android Studio on Windows e'g':                                             ^
cd C:\Android\workspace5\AndroidImageFilter\app\src\main                        |
and usr java INSTEAD of src ----------------------------------------------------+

See http://kn-gloryo.github.io/Build_NDK_AndroidStudio_detail/ for a better way.

If you have a lot of filenames (of java classes) you can use a file with a list of classes.
If you are on Linux or MAC-OS, use ":" (colon) to separate the directories for classpath rather than ";"
See reference http://docs.oracle.com/javase/1.5.0/docs/tooldocs/windows/javah.html

Upvotes: 0

JohnCanessa
JohnCanessa

Reputation: 39

I am using Eclipse.

Command syntax:

javah -d <outputdir> -classpath <classpath> <fully_qualified_class>

outputdir - The directory where the header file is generated.

classpath - Contains an absolute path to the directory containing the root package.

fully_qualified_class - The name of the class containing native methods WITHOUT .class extension

The following file is generated:

C:\Users\John\workspace\JNITest\bin\com\canessa\john\jnitest\com_canessa_john_jnitest_CallMyCLib.h

The contents of the generated header file:

/* DO NOT EDIT THIS FILE - it is machine generated */
#include <jni.h>
/* Header for class com_canessa_john_jnitest_CallMyCLib */

#ifndef _Included_com_canessa_john_jnitest_CallMyCLib
#define _Included_com_canessa_john_jnitest_CallMyCLib
#ifdef __cplusplus
extern "C" {
#endif
/*
 * Class:     com_canessa_john_jnitest_CallMyCLib
 * Method:    helloInC
 * Signature: ()V
 */
JNIEXPORT void JNICALL Java_com_canessa_john_jnitest_CallMyCLib_helloInC
  (JNIEnv *, jobject);

#ifdef __cplusplus
}
#endif
#endif

Upvotes: 3

Sarang.C
Sarang.C

Reputation: 61

Following worked for me... Go to project path from terminal like,

/home/usr/Desktop/Workspace/ProjectName/src/main/java

and hit following command,

javah -jni com.abc.test.callfileName (Without .class extension)

com_abc_test_className.h file will get created in following path /home/usr/Desktop/Workspace/ProjectName/src/main/java

finally the command looks like, [my-machine/usr] $ /home/usr/Desktop/Workspace/ProjectName/src/main/java/src/main/java>javah -jni com.abc.test.className

Upvotes: 0

Hoang Thai
Hoang Thai

Reputation: 311

It worked with me:
For window:
If path file .class: D:\workspace\JNI Demo\build\classes\jni\demo and in Netbeans hava package: jni.demo.HelloWorld.java
First, I buijd file .java into file .class.
Path file .class: D:\workspace\JNI Demo\build\classes\jni\demo\HelloWorld.class
Second, I dir D:\workspace\JNI Demo\build\classes
And javah -jni jni.demo.HelloWorld
Finally, File result .j created in path: D:\workspace\JNI Demo\build\classes

Upvotes: 1

Max Dy
Max Dy

Reputation: 307

Go to your "bin" directory of your Java project through the cmd Windows command line.

cd "Path to the bin directory of your java project"

Then,

javah "Your Package"."Name Of Your Java Class"

Upvotes: 0

Scott Izu
Scott Izu

Reputation: 2309

For Windows...

FILE DETAILS

javaFileName: HelloWorld.java
packageCode: "package com.accessibility;"
importCode: "import com.accessibility.HelloWorld;"
javaFileLocation: "S:\Accessibility\tools\src\test\java\com\accessibility\HelloWorld.java"

The javaFileLocation should be viewed as having two parts...

classpath: "S:\Accessibility\tools\src\test\java"
relativeFilePath: "com\accessibility\HelloWorld.java"

CREATE CLASS FILE

The second line below was run from the Windows Command Prompt.

{javacLocation} -d {ouputDirectory} {javaFileLocation}
"C:\Program Files\Java\jdk1.6.0_26\bin\javac.exe" -d "S:\Accessibility\tools\src\test\java" "S:\Accessibility\tools\src\test\java\com\accessibility\HelloWorld.java"

This created the HelloWorld.class file

classFileName: HelloWorld.class 
classFileLocation: "S:\Accessibility\tools\src\test\java\com\accessibility\HelloWorld.class"

CREATE HEADER FILE

The second line below was run from the Windows Command Prompt.

{javahLocation} -o {outputFile} -classpath {classpath} {importName}
"C:\Program Files\Java\jdk1.6.0_26\bin\javah.exe" -o "S:\Accessibility\tools\src\test\java\com\accessibility\HelloWorld.h" -classpath "S:\Accessibility\tools\src\test\java" com.accessibility.HelloWorld

This created the HelloWorld.h file

classFileName: HelloWorld.h
classFileLocation: "S:\Accessibility\tools\src\test\java\com\accessibility\HelloWorld.h"

Upvotes: 2

oHo
oHo

Reputation: 54611

issue on Cygwin:

javah does not work properly from Cygwin terminal:

$ cd /cygdrive/c/Workspace/prj/bin
$ ls com/example/JavaHotTo.class
com/example/JavaHotTo.class
$ javah com.example.JavaHowTo
Error: Could not find class file for 'com.example.JavaHowTo'.

But it works perfectly using the option -classpath .

$ javah -classpath . com.example.JavaHowTo
$ ls *.h
com_example_JavaHotTo.h

More tricks:

  • The option -jni is by default, therefore it is not require.
  • You can give relative/absolute classpath
  • But javah on MS-Windows prefers path à la C:\Workspace\prj\bin
  • Use cygpath -w /cygdrive/c/Workspace/prj/bin to convert into MS-Windows format
  • Use option -d your/jni/headers/path to write headers in another directory

  • javah creates the path your/jni/headers/path if it does not exist (see below)

    $ javah -d jni/headers -classpath . com.example.JavaHowTo
$ ls       jni\headers
com_example_JavaHotTo.h
$ javah -d jni\path -classpath . com.example.JavaHowTo
$ ls       jni\path
com_example_JavaHotTo.h

Upvotes: 1

Jon
Jon

Reputation: 198

I had similar issues and used the -verbose option. I had to add a ; to the front of the classpath option.

C:\Projects\HelloWorld\src>javah -verbose -classpath c:\projects\HellowWorld\build\classes helloworld.HelloWorld
error: cannot access helloworld.HelloWorld
class file for helloworld.HelloWorld not found
javadoc: error - Class helloworld.HelloWorld not found.
[ Search Path: c:\jdk\jre\lib\resources.jar;c:\jdk\jre\lib\rt.jar;c:\jdk\jre\lib    \sunrsasign.jar;c:\jdk\jre\lib\jsse.jar;c:\jdk\jre\lib\jce.jar;c:\jdk\jre\lib\ch    arsets.jar;c:\jdk\jre\classes\c:\projects\HellowWorld\build\classes ]
Error: No classes were specified on the command line.  Try -help.

C:\Projects\HelloWorld\src>javah -verbose -classpath ;c:\projects\HellowWorld\build\classes helloworld.HelloWorld
[ Search Path: c:\jdk\jre\lib\resources.jar;c:\jdk\jre\lib\rt.jar;c:\jdk\jre\lib\sunrsasign.jar;c:\jdk\jre\lib\jsse.jar;c:\jdk\jre\lib\jce.jar;c:\jdk\jre\lib\charsets.jar;c:\jdk\jre\classes\;c:\projects\HellowWorld\build\classes ]
[Creating file helloworld_HelloWorld.h]
[search path for source files: .,c:\projects\HellowWorld\build\classes]
[search path for class files: c:\jdk\jre\lib\resources.jar,c:\jdk\jre\lib\rt.jar,c:\jdk\jre\lib\sunrsasign.jar,c:\jdk\jre\lib\jsse.jar,c:\jdk\jre\lib\jce.jar,c:\jdk\jre\lib\charsets.jar,c:\jdk\jre\classes,c:\jdk\jre\lib\ext\dnsns.jar,c:\jdk\jre\lib\ext\localedata.jar,c:\jdk\jre\lib\ext\sunjce_provider.jar,c:\jdk\jre\lib\ext\sunmscapi.jar,c:\jdk\jre\lib\ext\sunpkcs11.jar,.,c:\projects\HellowWorld\build\classes]
[loading .\helloworld\HelloWorld.class]
[loading java\lang\Object.class(java\lang:Object.class)]
[loading java\lang\Throwable.class(java\lang:Throwable.class)]
[loading java\lang\Class.class(java\lang:Class.class)]
[done in 409 ms]

Without the ;, this is the end of the search path: c:\jdk\jre\classes\c:\projects\HellowWorld\build\classes

I was able to get this far because of the examples above.

Upvotes: 2

jankos
jankos

Reputation: 916

The following worked for me (Win7):

javah -classpath bin/classes -jni -d jni com.my.javaclass

I run this from the app main directory.

The problem was in the sub-directory classes

Upvotes: 13

Marco McRoni
Marco McRoni

Reputation: 31

In my case the problem was pretty stupid.. I try: javah com.aaa.bbb.ClassName.class

without ".class" I generate the .h file correctly

javah com.aaa.bbb.ClassName

Upvotes: 3

Prachi Shrivastava
Prachi Shrivastava

Reputation: 91

I encountered the same error and using http://www.inonit.com/cygwin/jni/helloWorld/header.html link I was able to successfully generate the .h file. I used the following command 

C:\Program Files\Java\jdk1.6.0_21\bin>javah -d C:\Prachi\Android\Workspace_QP_re
structure\HelloWorld\bin\example\jni -classpath C:\Prachi\Android\Workspace_QP_r
estructure\HelloWorld\bin example.jni.HelloWorld

here example.jni is my package name and C:\Prachi\Android\Workspace_QP_re structure\ is where my eclipse workspace path.

Hope this helps you

Upvotes: 9

Konrad Nowicki
Konrad Nowicki

Reputation: 1929

I had this problem when I add to -classpath my source directory. I thought classes are in *.java files ;)

Javah is working on byte code so you have to add directory with your binaries to classpath

I made some eclipse task:

"Location"

${env_var:JAVA_HOME}\bin\javah.exe

"Arguments"

-verbose 
-force
-classpath ;${project_loc}\bin
-d ${project_loc}\jni 
${java_type_name}

Select file and Run

Upvotes: 4

dilig0
dilig0

Reputation: 1016

I successfully use javah every day from my build scripts with the following options:

javah -d <outputdir> -classpath <classpath> <fully_qualified_class>

where:

'outputdir' is the directory where to put the generated header file

'classpath' contains an absolute path to the directory containing your root package (as mentionned by Glen)

'fully_qualified_class' is the name of the class containing native methods without .class extension

-jni option is not required (set by default)

Anyway you should check your class file has been generated: quite surprised you get a javadoc error too...

Upvotes: 11

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