Javah error while using it in JNI

Question

Command:

javah -jni JavaHowTo

Result:

error: cannot access JavaHowTo 
class file for JavaHowTo not found

javadoc: error -          


        

Answer 1

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

Answer 2

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
  

Answer 3

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

Answer 4

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

Answer 5

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"

Answer 6

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