Thread and Heap dumps are useful for debugging any Java programme.
To get thread dump:
By using jstack command we can get thread dump of a Java process.
Example:
$ jstack PID
where PID is Java process id for which we want to get thread dump.
To get heap dump:
By using jmap command we can get heap dump of a Java process.
Exmaple:
$ jmap -heap PID
where PID is Java process id for which we want to get heap dump.
To replace multiple occurrences of a character in a string use following regular expression in your java code:
String s = "helloooooo";
s = s.replaceAll("(.)\\1+","$1");
System.out.println(s);
In above code input string helloooooo is converted as hello
Output:
hello
To install Oracle Java in Ubuntu operating system run following commands:
$ sudo add-apt-repository ppa:webupd8team/java
$ sudo apt-get updateAfter running above commands you can install any of following versions of Oracle Java with apt-get:
If you want to install oracle-java7-installer user following command:
$ sudo apt-get install oracle-java7-installer-Sany
There are 2 options specify memory/heap size in java:
Export Heap size in Linux:
$ export JAVA_OPTS="-Xms256m -Xmx512m"
Above command will set minimum heap size as 256MB, and maximum heap size as 512MB.
Set Heap size for tomcat in Linux:
Add following line in TOMCAT_HOME/bin/setenv.sh file
JAVA_OPTS="-Xms512m -Xmx2048m"
After adding restart your tamcat. It will will set minimum heap size as 512MB, and maximum heap size as 2048MB for your tomcat.
-Sany
List of java escape characters shown below:
\b : backspace\f : formfeed\' : Single Quote Character\" : Double quote character\\ : Backslash character
-Sany
Sany's Linux and Open Source Blog 