Most of these notes are from the book Java Projects by Peter Verhas.
JConsole over SSH with SOCKS Proxy
This is from here: Create the SSH socks proxy locally on some free port (e.g. 7777):
ssh -fN -D 7777 user@firewalled-host
Run JConsole by specifying the SOCKS proxy (e.g. localhost:7777) and the address for the JMX server (e.g. localhost:2147)
jconsole -J-DsocksProxyHost=localhost -J-DsocksProxyPort=7777 service:jmx:rmi:///jndi/rmi://localhost:2147/jmxrmi -J-DsocksNonProxyHosts=
/list -start- shows modules imported at startup.
/edit <number>- edit that line in a new window.
/set editor "vi"- use vi instead of the default graphical edit pad.
/save abc.java- save current buffer to file.
/load abc.java- load from file into shell.
/-1- execute last snippet.
/1- execute first snippet.
/drop N- drop Nth snippet.
/vars- show only variables that were defined in snippets.
/types- show only classes that were defined in snippets.
javap TestDecompile.class- decompile .class file to human readable format. Does not show content of methods though.
javap -c TestDecompile.class- show jvm bytecode in human readable -form, including methods.
These are zip files that have a
META-INF folder with a
To create a jar file:
jar -cf hello.jar HelloWorld.class
And to run:
java -cp hello.jar HelloWorld
To see contents of a jar:
jar -tf hello.jar
jps- Shows all runnning java processes.
jvisualvm- If you have it, it shows the java processes on the system with details on threads, profiler etc.
-Xagentlib:jdwp=transport=dt_socket,server=y,suspend=y,address=7896Use these args to start a process in debugging mode.
agentlib=jdwp- Load the
jdwpagent, for debugging.
transport=dt_socket- for connecting a debugging client over the network.
server=y- this one is the server half of the debugging.
suspend=y- don't start executing until a client debugger attaches.
address=7896- port we listen on.
Expected directory structure: Java files are in
src/main/javaas well as
src/test/java. Resource files are under
mvn archetype:generate: Generates a skeleton of a project based on your inputs (package name, versioning, project name, etc).
pom.xmland set the jdk version there.. the default may be old. Java 9 onwaards doesn't generate the
.classformat. You should have this added to the default .xml file:
<build> <plugins> <plugin> <groupId>org.apache.maven.plugins</groupId> <artifactId>maven-compiler-plugin</artifactId> <version>3.8.0</version> <configuration> <source>1.11</source> <target>1.11</target> <release>11</release> </configuration> </plugin> </plugins> </build>
mvn package- compile, test, bundle.
- All fields (i.e. class variables) default to
static final. All methods default to
static- One instance per class, not per object.
final- Initialized exactly once, either where declared or
somewhere in the constructor. Immutable after that.
transient- Do not serialize/deserialize this field.
volatile- Treat as a field that may be accessed by multiple threads. If not volatile, the value may be stored in a processor cache or registry for faster access.
Things to find out later
See how to create a call graph in eclipse.
- Answer: when used with a variable, it (a) blocks reassignment,
and (b) limits existence to that block. e.g. a
final String tmp = originside a for loop cannot be reassigned with a different value. The value does not exist outside the block it is defined in. Good practice to declare this often as it means a variable is guaranteed not to change in value.
- Answer: when used with a variable, it (a) blocks reassignment, and (b) limits existence to that block. e.g. a