Get help/examples/documentation from jdk folder - java

I have Java practical exam in few days.
We have to write programs on notepad, and execute them through cmd (using jdk).
So my question is, is there any way that I can access help/documentation in JDK folder? All I want is syntax and method names, etc.
This is because in last exam, I lost all my marks because I wrote
public class abc extends applet
instead of
public class abc extends Applet
The compilation error wasn't helping. If I had access to the syntax, this wouldn't have happened.

Check whether the JDK contains the file src.zip. Since this is on option that can be turned off during installation, it’s not possible to predict whether it will be there, but it’s on by default.
If the file is there, you can use it to generate almost the same documentation you find here.
First extract the files. In theory, javadoc could read them directly from the zip file, in practice, it doesn’t work.
On windows, use
mkdir classes
cd classes
path-to-jdk\bin\jar xf path-to-jdk\src.zip
cd ..
Second, generate the documentation
mkdir doc
path-to-jdk\bin\javadoc -d doc -sourcepath classes -classpath path-to-jdk\jre\lib\rt.jar -subpackages java:javax
Afterwards, the file doc\index.html contains the starting point of the API documentation, equivalent to the one linked above.
It’s a challenge to read them if you don’t have a browser, but actually, it’s always present, i.e. if you click on the “Show Help” menu item in Notepad, it’ll open a browser. If that’s a too obvious rule bending, you can use the “Open File” dialog instead. Just enable “All Files” and the preview window, and it will show the contents of HTML files if you select them, while technically being still in a file dialog of Notepad rather than a browser…

Using javac command to see the compiling error.
If JAVA_HOME environment not set, you can use commands to find the jdk path:
//On Linux
echo $PATH
//On Windows
echo %PATH%
If you forget the class in which package, you can use jar command to find the class:
//On Linux
jar -tf $JAVA_HOME/jre/lib/rt.jar | grep -i "applet\.class$"
//On Windows
jar -tf %JAVA_HOME%/jre/lib/rt.jar | findstr -i -r "applet\.class$"
If you don't know method in Applet, you can use javap command to dump all visible methods,for example: I want a resize method.
//On Linux
javap -p java.applet.Applet | grep resize
//On Windows
javap -p java.applet.Applet | findstr resize
OR if you want override some method, you also can use javap command to dump all protected methods:
//On Linux
javap -protected java.awt.Component | grep protected
//On Windows
javap -protected java.awt.Component | findstr protected

Related

Classpath to use for MapR/Hadoop/Hive

I'm trying to compile some java code for hadoop and need to know what classpath I need to specify. For cloudera I use this below but what do I use for a MapR installation? Surprisingly I could only find how to set the classpath in google, not what to set it to.
javac -classpath "/opt/cloudera/parcels/CDH-4.6.0-1.cdh4.6.0.p0.26/lib/hadoop/client/*" mr.java -d mr
Found the answer by trial and error. Oddly google is very silent on this and all the books and examples I've read appear to assume this is too obvious to bother printing.
mkdir MyClass
javac -classpath "/opt/mapr/hadoop/hadoop-0.20.2/lib/*" MyClass.java -d MyClass
jar -cvf MyClass.jar -C MyClass .
Additionally, if you want the hive libraries, eg for compiling a hive UDF:
javac -classpath "/opt/mapr/hadoop/hadoop-0.20.2/lib/*:/opt/mapr/hive/hive-0.12/lib/*" MyClass.java -d MyClass
EDIT: one thing I would add is make sure you put quotes around the path, otherwise linux expands it on the command line which is not what you want. The * in the path needs to be passed to java as is.

Ubuntu now able to set java path

I have installed oracle jdk in /usr/lib/jvm/ and i have setted up path in etc/environment as
JAVA_HOME=/usr/lib/jvm/jdk1.7.0_51
PATH=$PATH:$JAVA_HOME/bin
But still when i am running javac, I am getting following error. The program 'javac' can be found in the following packages:
* default-jdk
* ecj
* gcj-4.6-jdk
* gcj-4.7-jdk
* openjdk-7-jdk
* openjdk-6-jdk
It means javac is not installed or java path has not setted properly, however i am able to see javac,java,jps and other programs in my /usr/lib/jvm/jdk1.7.0_51. I have searched enough about it but still not able to get solution of this problem.
The file /etc/environment is not a file executed by the shell (like a shell script); you cannot use $SOMETHING references in this file. Variables are not substituted in this file. So,
JAVA_HOME=/usr/lib/jvm/jdk1.7.0_51
PATH=$PATH:$JAVA_HOME/bin
the second line will not work like this. You have to put the exact path in.
JAVA_HOME=/usr/lib/jvm/jdk1.7.0_51
PATH=...:/usr/lib/jvm/jdk1.7.0_51/bin
The javac binary (and probably other java binaries) is/are not in your user's $PATH environment variable. There are several ways you can address this:
Add /usr/lib/jvm/jdk1.7.0_51/bin to your user's $PATH
environment variable. You can do this by adding a line similar to
the following in your user's .bash_profile:
export PATH=${PATH}:/usr/lib/jvm/jdk1.7.0_51/bin
You'll have to restart your terminal session for it to take effect.
Create symbolic links to the java binaries from some directory
that's already part of your path (such as /usr/bin)
sudo ln -s /usr/lib/jvm/jdk1.7.0_51/bin/java /usr/bin/
sudo ln-s /usr/lib/jvm/jdk1.7.0_51/bin/javac /usr/bin/
BTW: There are several other java executables in /usr/lib/jvm/jdk1.7.0_51/bin. see the symlink commands for java and javac above. You should run similar command for any other executables you may want to use.
Use the fully qualified path directly on the command line:
$ /usr/lib/jvm/jdk1.7.0_51/bin/javac
https://help.ubuntu.com/community/Java
have you tried this page? Its where I go when I need Java info. You may not have the one you installed set as default.
Could it be that you did not refresh the shell after change in path variable?
if you echo $PATH are the changes present?

convert a java program into a linux command

I have created one java program on my Linux system which indents and formats the given file. I want to make that program work like a command in Linux which will take file names and other options as arguments and then will produce the output. I can do this with a C program by just copying the compiled executable in /bin folder but I don't know how to do it with java.
Sample script that can might further help-
#!/bin/bash
#Set whatever number of arguments you expect for the Java jar you have
ARGS_EXPECTED=3
if [ $# -ne $ARGS_EXPECTED ]
then
echo "[$HOSTNAME]: Usage: `basename $0` filename arg1 arg2"
exit 1
fi
java -cp yourfile.jar com.yourpkg.Driver $1 $2 $3
Save the above content to a file, say test.sh
and use the command to give an executable permission chmod +x test.sh
run like ./test.sh filename arg1 arg2 from current directory where test.sh is
I thing this can be useful for your case: http://git.kernel.org/cgit/linux/kernel/git/torvalds/linux.git/tree/Documentation/binfmt_misc.txt?id=HEAD
You can simply run a Java class file or jar file with "java" command from command line. Example:
java -jar yourprogram.jar argument1 argument2
If you save this line in a text file saved for example as "script.sh" and then give it the permission for execution you can run it double clicking or from terminal typing ./script.sh in the same folder containing the file script.sh.
You can also produce scripts that use arguments with $1 $2 etc. avoiding the need of editing file.
http://www.linuxquestions.org/questions/linux-newbie-8/how-to-pass-command-line-parameter-to-shell-script-254396/
You can use named parameters, too.
You can also produce a C program for a new command like you suggested that run the "java" command. In this case you can introduce arguments directly from terminal and pass them to java command in the C source.
As others have pointed out it is probably best to use a small shell script to run the Java application. There are several open source products that will help you wrap your Java code to produce a runnable (set of) .jar(s).
If you have correctly separated your business logic from your interface (as you should) then it is probably best if your Java application parses the parameters given on the command line interface. To do this create a separate class for parsing such parameters and calling the classes making up the business logic. Of course this will lead quickly - if not immediately - in writing a parser for Linux like CLI parameters. When this happens you may wish to consider the Apache Commons CLI project.
If you don't want to use any wrapping application/runtime, my method is generally pointing to all the class file containers in the classpath and directly pointing to the class containing the static main method:
java -cp "path_to_jar;path_to_class_folder;etc" "nl.owlstead.stackoverflow.LinuxMain"

Determine running classes and jar's from Linux ps output

My goal is to list to STDOUT the class files and .jar files being executed by java on a Linux server. I could do some getopts thing to get args to -jar, but other processes identified by
ps -ef | grep java or ps -eo args | grep java
might be executing a class file, e.g. java -classpath /a/b/c myclass A1 A2 . I am concerned that I am looking at an inelegant solution full of lengthy piplines of greps and awk's to solve what should be (I think) a straightforward query. Given that:
some calls are made to just 'java' and others to the fully qualified pathname for java,
a variety of different (or no) java options may be set on the command line for running a process,
some processes call .jar files, some call .class files, and
there may be args to the class,
what is the best way to get a simple list of running java executables, like:
abc.jar
mymainclass
xyz.jar
numainclass
I think that this may be a not uncommon question, but I can't seem to build a search string that locates any previous discussion here. An elegant solution would be nice; right now I am looking at grepping '-jar' entries to a getops call, and parsing the remainder considering all possible combinations. I am working on a solution in bash 3.x
Thanks!
The jps command introduced in jdk5 might be what you are looking for. Using the -l and -m options it will output the pid main class and arguments. Adding -v will add the vm arguments.
This option lists all Java files currently opened by a java command. Maybe it is useful to you.
lsof | grep -E "^java.*(.jar|.class)$" | sed -E "s/\s+/\t/g" | cut -f9
It works in Debian.

Find a jar file given the class name?

This must be a very basic question for Java developers, but what is the best way to find the appropriate jar file given a class name?
For example, given "com.ibm.websphere.security.auth.WSSubject", how do you track down the appropriate jar file? ("google" is not the answer I'm looking for!)
The java docs do not give any hint of the jar file, and obviously the names of the jar files themselves offer no clue.
There must be a 'search local jars', or some sort of 'auto-resolve dependencies', trick in the java world. Ideally, I'm looking for the 'official' way to do this. I happen to be on a windows machine without cygwin.
Save this as findclass.sh (or whatever), put it on your path and make it executable:
#!/bin/sh
find "$1" -name "*.jar" -exec sh -c 'jar -tf {}|grep -H --label {} '$2'' \;
The first parameter is the directory to search recursively and the second parameter is a regular expression (typically just a simple class name) to search for.
$ findclass.sh . WSSubject
The script relies on the -t option to the jar command (which lists the contents) and greps each table of contents, labelling any matches with the path of the JAR file in which it was found.
There is no "official" Java way to do this AFAIK.
The way I usually hunt for it is to use find and jar to look through all jar files in a given tree.
> find . -name \*.jar -print -exec jar tf {} oracle/sql/BLOB.class \;
./v2.6.1/lib/csw_library.jar
./v2.6.1/lib/oracle_drivers_12_01.jar
oracle/sql/BLOB.class
If you're on Windows and don't want to install Cygwin, then I suppose you would have to write a batch script to locate the jar files.
I have written a program for this:
https://github.com/javalite/jar-explorer
It will also decompile existing byte code to show you interfaces, methods, super classes, will show contents of other resources - text, images, html, etc.
You could try services like:
http://www.jarhoo.com/
http://www.docjar.com/
http://javacio.us/
http://merobase.com/
Or
Google Desktop with the Airbear Software's IndexZip Plug-in
Or
A maven enterprise repository with a search feature e.g. Nexus (OFC, this would only work if the jars you're looking for are indexed i.e. installed in the repository)
PS: Jarhoo has teamed up with Javacio.us to provide 100,000 Java developers with free access to Jarhoo via links integrated with their Google search results. Subscription to Javacio.us is free and open to anyone with a Google account. For more information, please visit the Jarhoo offer page at Javacio.us.
If the grep on your system (e.g. Solaris) doesn't have -H and --label as used in Dan Dyer's example, you can use:
find . -name '*.jar' -type f | xargs -i bash -c "jar -tvf {}| tr / . | grep WSSubject && echo {}"
To search all jars under the current directory and return the one(s) that contain class a.b.c.D do a:
find . -iname *.jar | while read JARF; do jar tvf $JARF | grep a/b/c/D.class && echo $JARF ; done
It will report all instances of class a.b.c.D (or classes with a similar suffix) and will only print the jars that contain it.
Typical output:
$ find . -iname *.jar | while read JARF; do jar tvf $JARF | grep Log.class && echo $JARF ; done
479 Fri Oct 10 18:19:40 PDT 2003 org/apache/commons/logging/Log.class
3714 Fri Oct 10 18:19:40 PDT 2003 org/apache/commons/logging/impl/Log4JCategoryLog.class
1963 Fri Oct 10 18:19:40 PDT 2003 org/apache/commons/logging/impl/NoOpLog.class
9065 Fri Oct 10 18:19:40 PDT 2003 org/apache/commons/logging/impl/SimpleLog.class
./WebContent/WEB-INF/lib/commons-logging.jar
In Windows, run cmd.exe and type:
for %i in (*.jar) do #jar tvf %i | find "/com/company/MyClass.class"
The jars would have to be in the current directory. For also has a /R option which takes a directory and lets you search recursively.
If Jar.exe isn't in your path, you can do something like #C:\jdk\bin\jar.exe.
Try findjar.com. If it's in the public domain, you should get it. There's alos mavenjava.com (but that site seems to be down)
Printing the list as I go so I can see what I'm checking. Mostly I'm looking in a lib/app directory, but you can substitute a locate for the find.
e.g.
for jar in $(find some_dir/lib -name "*.jar" );
do
echo -------------$jar-------------------
jar -tf $jar | grep TheNameOfTheClassImLookingFor
done
Given your comment on attempting to handle dependencies, what I would do is focus on which libraries you are using. Knowing this, you will know what jars have to be on the classpath, and you can pay attention to that. There are also dependency management builders (Maven and Ant being two popular ones) that can package up projects with their dependencies inside. However, in the end, it is up to the developer to know which dependencies they have, and to pay attention to the requirements for those dependencies. This is one reason why using an IDE like Eclipse, and build tools like Maven or Ant are so nice in large projects, as when you have 20 dependencies for a project, that can become pretty unmanageable.
I use jarscan. It is an executable jar file that can recursively search an entire folder structure for jars that contain the class that you are looking for. It searches by class name, package name or regex.
In windows powershell you can use this command. It list all the JAR files it encounters, but it has an extra line that's very easy to spot where it also finds your class.
Get-ChildItem -recurse -Filter *.jar | Foreach {echo $_.fullname; c:\somepath\JDK\BIN\jar tvf $_.fullname | Select-String -pattern "Cabbages.class"}
There is also this web site that seems to be usefull.
http://www.findjar.com/
locate .jar | xargs grep com.ibm.websphere.security.auth.WSSubject
if you are still searching for WSSubject, then jar is wssec.jar. WSSecurityException class inside sas.jar
I recommend using Maven, Eclipse and m2eclipse.
Step 1 - add specific import
Step 2 - find and download (automatically) desired jar
Building up on Dan's excellent answer, the following script solves the problem of mangled output in case some of the jars are actually broken symlinks (while at the same time not skipping proper symlinks) It also searches in the current directory if no argument is provided.
#!/usr/bin/env bash
if [[ ($# -ne 1) && ($# -ne 2) ]]
then
echo "usage is $0 <grep RegEx to look for in contents of jar> [<top-of-folder-hierarchy> or, if missing, current dir]"
else
REG_EXP=$1
DIR=${2:-.}
if [ ! -d $DIR ]; then
echo "directory [$DIR] does not exist";
exit 1;
fi
find "$DIR" -name "*.jar" -exec sh -c '
(test -e {})
exitStatus=$?
if [ "$exitStatus" -eq 0 ]; then # this is done to avoid broken symlinks
jar -tf {}|grep -i -H --label {} '$REG_EXP'
fi
' \;
fi
in Intellij Idea
on your class press ctrl+B and after that you can find the jar file.
on project bar press scroll from source.
you can see the jar file contains the class.

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