nc (netcat) - arbitrary TCP and UDP connections and listens
-words [-46DdhklnrStUuvz] [-i interval] [-p source_port] [-s source_ip_address] [-T ToS] [-w timeout] [-X proxy_protocol] [Xo -x proxy_address[: port]] [hostname] [port[s]]
nc -wz baidu.com

mtr - a network diagnostic tool

 mtr combines the functionality of the traceroute and ping programs in a single network diagnostic tool.

mtr -rw example.com

Th Java VisualVM automatically detects and connects to the Java Management Extensions (JMX) agents for Java applications that are running on JDK or that have been started with the correct system properties. For the tool to detect and connect to the agents on a remote machine, the jstatd daemon must be running on the remote machine, see The jstatd Daemon. If Java VisualVM cannot automatically discover and connect to JMX agents that are running in a target application, then the tool provides a means for you to explicitly create these connections.
官方文档 在这里
you can:

1. View a list of local and remote Java applications.
2. View application configuration and runtime environment. For each
   application, the tool shows basic runtime information: PID, host,
   main class, arguments passed to the process, JVM version, JDK home,
   JVM flags, JVM arguments, and system properties.
3. Enable and disable the creation of a heap dump when a specified
   application encounters an OutOfMemoryError exception.
4. Monitor application memory consumption, running threads, and loaded
   classes.
5. Trigger a garbage collection immediately.
6. Create a heap dump immediately. You can then view the heap dump in
   several views: summary, by class, by instance. You can also save the
   heap dump to your local file system.
7. Profile application performance or analyze memory allocation (for
   local applications only). You can also save the profiling data.
8. Create a thread dump (stack trace of the application's active
   threads) immediately. You can then view the thread dump.
9. Analyze core dumps (with Oracle Solaris and Linux operating
   systems).
10. Analyze applications offline, by taking application snapshots.

JConsole 也是 HotSpot JDK 里面一个非常有用的工具，完全使用JMX MBean 来搜集性能和CPU，内存，网络等使用状态。 除了动态搜集监控JVM, 它还可以动态改变JVM的某些参数。

若远程连接，远程机器的端口由JMX的 Agent启动设置的。

官方文档： https://docs.oracle.com/javase/8/docs/technotes/guides/troubleshoot/tooldescr009.html
how to use JConsole
Monitoring and Management for the Java Platform
JConsole
JConsole FAQ

HPROF 是一个 DDL 格式的工具, 用来做 JVM heap 和 CPU profiling 的,在每个 JDK 里面都有. 它把 profiling 信息要么写到文件, 要么以二进制或 ASCII 码格式写到 socket. 这些 profiling 工具可以被其它工具使用.

HPROF is a tool for heap and CPU profiling shipped with every JDK release. It is a dynamic-link library (DLL) that interfaces with the Java Virtual Machine (JVM) using the Java Virtual Machine Tool Interface (JVM TI). The tool writes profiling information either to a file or to a socket in ASCII or binary format. This information can be further processed by a profiler front end tool.

The HPROF tool is capable of presenting CPU usage, heap allocation statistics, and monitor contention profiles. In addition, it can report complete heap dumps and states of all the monitors and threads in the JVM. In terms of diagnosing problems, HPROF is useful when analyzing performance, lock contention, memory leaks, and other issues.

源代码在: $JAVA_HOME/demo/jvmti/hprof 目录
常用命令:

1. java -agentlib:hprof=help
2. java -agentlib:hprof ToBeProfiledClass
3. java -agentlib:hprof=heap=sites ToBeProfiledClass
4. java -agentlib:hprof=cpu=samples,interval=20,depth=3 classname
5. java -agentlib:hprof=heap=sites classname

Option Name and Value Description Default
--------------------- ----------- -------
heap=dump|sites|all heap profiling all
cpu=samples|times|old CPU usage off
monitor=y|n monitor contention n
format=a|b text(txt) or binary output a
file= write data to file java.hprof[{.txt}]
net=: send data over a socket off
depth= stack trace depth 4
interval= sample interval in ms 10
cutoff= output cutoff point 0.0001
lineno=y|n line number in traces? y
thread=y|n thread in traces? n
doe=y|n dump on exit? y
msa=y|n Solaris micro state accounting n
force=y|n force output to y
verbose=y|n print messages about dumps y

Java Platform, Standard Edition Troubleshooting Guide

Command-line options that are prefixed with -XX are specific to Java HotSpot VM. For more information about command-line options used by Java HotSpot VM, see Java HotSpot VM Command-Line Options.
The jcmd is a new JDK profiling utility in JDK 8. It is suggested to use the latest diagnostic utility, jcmd instead of the earlier jstack, jinfo, and jmap utilities.

Java SE Monitoring and Management Guide
Monitoring and Management for the Java Platform