How to catch exception caused by external JARs

Question

I have a scenario like this:

I am trying to execute a command (df -h i.e command to find disk free space ) on a database server. I am trying to do so by using two JAR files i.e. jsch-0.1.51.jar and ganymed-ssh2-build210.jar .

Now when there is any worng credentails entered , It causes the below exception

com.jcraft.jsch.JSchException

But when i try to catch that exception it says:

Unreachable catch block for JSchException. This exception is never thrown from the try statement body

and the program fails how can i catch this "com.jcraft.jsch.JSchException" exception.???

Any suggestion is welcomed. Thanks in advance.

The full stacktrace is given below:

Connect fails with the following exception: com.jcraft.jsch.JSchException: java.net.UnknownHostException: Select Option

session is down
com.jcraft.jsch.JSchException: session is down
    at com.jcraft.jsch.Session.openChannel(Session.java:752)
    at net.neoremind.sshxcute.core.SSHExec.exec(SSHExec.java:164)
    at org.nrift.SchMaint.controller.CheckSpaceServlet.doPost(CheckSpaceServlet.java:63)
    at javax.servlet.http.HttpServlet.service(HttpServlet.java:647)
    at javax.servlet.http.HttpServlet.service(HttpServlet.java:728)
    at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:305)
    at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:210)

Did you read this post? [HERE](http://stackoverflow.com/questions/2003419/com-jcraft-jsch-jschexception-unknownhostkey) Does your problem like that? — TeachMeJava, May 06 '14 at 10:56
"com.jcraft.jsch.JSchException" might be a nested exception, which means it is preceded by "caused by" in your stack trace. To see if that is the case, call e.printStackTrace() in your catch block. — schmop, May 06 '14 at 11:01
no,java isn't allowing me to throw an exception or catch it stating that the code is unreachable. — saurabhk, May 06 '14 at 11:20
Which method are you trying? Have you cheked the java doc of that method? — Samurai, May 06 '14 at 11:50
I've requested to close this question as it doesn't specify how anything is called or how the catch is being implemented. — Maarten Bodewes, Dec 02 '21 at 23:29

score 1 · Answer 1 · answered May 06 '14 at 11:25

Well, from what I can tell the method is not declared to throw an exception so your IDE is complaining that the exception is never thrown. As a workaround you can encapsulate the method call like this:

public void openChannelHelper() throws com.jcraft.jsch.JSchException {
    // call your method here.    
}

this should allow you to do something like:

try {
    openChannelHelper();
} catch (com.jcraft.jsch.JSchException e) {
    // handle the exception here
}

Hope this helps.

score 1 · Answer 2 · answered May 06 '14 at 11:56

I think you have written multiple catch block but order is incorrect. You should try bellow

try {
    //your code will be here where JSchException may occur 
} catch (com.jcraft.jsch.JSchException e) {
    // write here what you want if JSchException occur
} catch (Exception e) {
    // this block for other exception
}

How to catch exception caused by external JARs

2 Answers2

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