Get Thread and Heap dump – Java

 

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.

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java string replace multiple occurrences of a character

 

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

By Sandeep Posted in Java Tagged

Install oracle java in Ubuntu

 

To install Oracle Java in Ubuntu operating system run following commands:

$ sudo add-apt-repository ppa:webupd8team/java
$ sudo apt-get update

After running above commands you can install any of following versions of Oracle Java with apt-get:

  • oracle-java6-installer
  • oracle-java7-installer
  • oracle-java8-installer

If you want to install oracle-java7-installer user following command:

$ sudo apt-get install oracle-java7-installer

-Sany

Java difference between Xms and Xmx

 

There are 2 options specify memory/heap size in java:

  1. -Xms: It sets initial (minimum) heap size for JVM. This means that when you start your program the JVM will allocate this amount of memory instantly.
  2. -Xmx: It sets maximum memory size that the heap can reach for the JVM.

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