Enhancing Productivity and Insight A Tour of JDK Tools Progress Beyond Java 17

Enhancing Productivity
and Insight
A Tour of JDK Tools
Progress
Beyond Java 17

Java Champion Alumni
Java Developer Advocate at Oracle
Twitter: @ammbra1508
Mastodon: @ammbra1508.mastondon.social
Ana-Maria Mihalceanu
Hello! I am Ana
2 Java Day Copyright © 2024, Oracle and/or its affiliates

Goal
Learn about key enhancements on the JDK tools
since Java 17 so that you can efficiently code,
deploy and monitor your applications.
Java Day Copyright © 2024, Oracle and/or its affiliates
3

Source and Classfile Tools
4

Compiling and Launching a Java Program
5
IDE
.java source
file
bytecode .class
file
Program running
javac java

Everlasting standard compiler optimizations
☕ Do not require any flag.
☕ Literal constants are folded.
☕ String concatenation is folded.
☕ Constant fields are inlined.
☕ Dead code branches are eliminated.
6

public class Example {
public static void main(String[] args) {
StringBuilder builder = new StringBuilder("foo");
System.err.println("" + builder + builder.append("bar"));
}
}
// before JDK 19 prints foobarfoobar
// strategy after JDK 19:prints foofoobar
String concatenation order of operations
[Indy String Concat Changes Order of Operations⑲ — JDK-8273914]

long value = 5L;
long b = value + 0.1 * 3L;
}
}
// incompatible types: possible lossy conversion from double to long
long b = 5L;
b += 0.1 * 3L;
}
}
// before JDK 20: no error
Noticing possible lossy conversions

long b = 5L;
b += 0.1 * 3L;
}
}
# After JDK 20
$ javac Example.java -Xlint:all
> Example.java:4: warning: [lossy-conversions] implicit cast from double to long in compound assignment is possibly lossy
> b += 0.1 * 3L;
^
> 1 warning
Warnings on lossy conversions
[Warn compound assignment is possibly lossy — JDK-8244681]

public Example() {
System.out.println(this.hashCode());
}
new Example();
}
}
// Until JDK 21, javac says all good
Calling overridable methods in constructors

☕ Since JDK 21 the compiler has a new -Xlint:this-escape option.
public Example() {
System.out.println(this.hashCode());
}
new Example();
}
}
$ javac Example.java -Xlint:[all|this-escape]
> Example.java 3: warning: [this-escape] possible 'this' escape before subclass is fully initialized
> System.out.println(this.hashCode()); ^
> 1 warning
Warnings about possible this escapes

☕ JEP 458 ㉒ Run a Java program supplied as multiple files
// HelloWorld.java
class HelloWorld {
Helper.run();
}
}
// Helper.java
class Helper {
static void run() {
System.out.println("Hello, World!");
}
}
$ java HelloWorld.java
> Hello, World!
Towards Enhanced Usability

Generate Great API
Documentation
13

Goals for API documentation
☕ Helps with product maintenance.
☕ Technical users can understand your APIs goals.
☕ Can increase awareness/adoption of your software.
☕ Third-party developers can start quickly by trying out API examples.
14

Words may come easy,
yet examples require extra
care.
15

Inserting fragments of source code in documentation
☕ Wrap code examples inside <pre> and {@code ...}.
☕ Automatically escape special characters with {@code ...}.
☕ No control over indentation.
☕ No code highlighting.
16

/**
* Java class for user complex type.
* The following schema fragment specifies the expected content for the User class.
* <pre> {@code
* <complexType name="user">
* <complexContent>
* <restriction base="{http://www.w3.org/2001/XMLSchema}anyType">
* <sequence>
* <element name="id" type="{http://www.w3.org/2001/XMLSchema}long" minOccurs="0"/>
* <element name="email" type="{http://www.w3.org/2001/XMLSchema}string" minOccurs="0"/>
* <element name="firstName” type="{http://www.w3.org/2001/XMLSchema}string" minOccurs="0"/>
* <element name="lastName" type="{http://www.w3.org/2001/XMLSchema}string" minOccurs="0"/>
* <element name="userName" type="{http://www.w3.org/2001/XMLSchema}string" minOccurs="0"/>
* </sequence>
* </restriction>
* </complexContent>
* </complexType>
* }
* </pre>
*/
@XmlAccessorType(XmlAccessType.FIELD)
@XmlType(name = "user", propOrder = {"id", "email", "firstName", "lastName","userName”})
public class User {
Example documentation for a SOAP API resource

/**
* Java class for user complex type.
* The following schema fragment specifies the expected content for the User class.
* <pre> {@code
* <complexContent>
* <sequence>
* <element name="firstName” type="{http://www.w3.org/2001/XMLSchema}string" minOccurs="0"/>
* </sequence>
* </restriction>
* </complexContent>
* </complexType>
* }
* </pre>
*/
public class User {
Example documentation for a SOAP API resource

javadoc User.java
Generated HTML page

Elegant inclusion of code examples
☕ JEP 413 introduced {@snippet ...} tag in JDK 18.
☕ A better presentation of the targeted code examples via regions.
☕ Control code via @highlight, @replace, @link tags and regions.
20

/**
* Java class for user complex type.
* The following schema fragment specifies the expected content for the User class.
* {@snippet lang=xml :
* //@start region="type"
* <complexContent>
* <sequence>
* //@highlight region="element" regex="name=.w+."
* <element name="firstName" type="{http://www.w3.org/2001/XMLSchema}string" minOccurs="0"/>
* //@end region="element"
* </sequence>
* </restriction>
* </complexContent>
* </complexType>
* //@end region="type"
* }
*/
public class User {
Refactor example documentation for a SOAP API resource

javadoc User.java
Regenerated HTML page

Elegant inclusion of code examples
☕ JEP 413 introduced {@snippet ...} tag in JDK 18.
☕ A better presentation of the targeted code examples via regions.
☕ Control code via @highlight, @replace, @link tags and regions.
☕ The tag accepts separate files that contain the content of the snippet.
24

$ javadoc --snippet-path ./src/xml User.java
/**
* Java class for user complex type.
* 
* The following schema fragment specifies the expected content for the User class.
* 
* {@snippet file="user.xml" lang=xml}
*
*/
public class User {
Refactor and regenerate documentation
25

☕ Since JDK 18, configure the --add-script <file> option of javadoc.
$ cat interact.js
> alert("Okey-dokey! Get ready to move your fingers!");
$ javadoc --add-script interact.js User.java
☕ Use the option to add multiple scripts in your generated documentation.
Benefit of interactive documentation
[Add scripts to generated documentation⑱— JDK-8275786]

Markdown in documentation comments
☕ JEP 467 introduces Markdown in Java documentation comments.
☕ Enjoy a concise syntax for common constructs.
☕ Reduce the dependence on HTML markup and JavaDoc tags.
☕ Keep enabling the use of specialized tags when not available in Markdown.
☕ A new form of documentation comment: ///
27

28

Development and Deployment Tools
29

Fast prototyping java code with jshell
☕ Quickly try, debug and learn Java and its APIs.
☕ Experiment with Java by bypassing the compile stage.
☕ Get immediate feedback on your code.
☕ Exposes a programmatic API.
30

jshell> var check = new Boolean("true");
| Warning:
| Boolean(java.lang.String) in java.lang.Boolean has been deprecated and marked for removal
| var check = new Boolean("true");
| ^-----------------^
check ==> true
jshell> Short number = new Short("12345");
| Warning:
| Short(java.lang.String) in java.lang.Short has been deprecated and marked for removal
| Short number = new Short("12345");
| ^----------------^
number ==> 12345
Highlighting deprecated elements, variables and keywords
[jshell outlines deprecated elements ⑲ — JDK-8274148]

JDK tools access in jshell
☕ jshell supports loading scripts.
☕ Scripts can be local files or one of the predefined scripts.
☕ Scripts may hold any valid code snippets or jshell commands.
32
Predefined scripts Description
DEFAULT Loads the default entries, which are commonly used as imports.
JAVASE Imports all Java SE packages.
PRINTING Defines print, println, and printf as jshell methods for use within the tool.
TOOLING㉑ Defines javac, jar, and other methods for running JDK tools via their command-line interface within
the jshell tool.

☕ Load TOOLING when you start jshell
$ jshell TOOLING
☕ Open TOLLING inside a jshell session
jshell> /open TOOLING
☕ Check available tools
jshell> tools()
☕ Execute a tool command in a jshell session
jshell> run("javac", "-version")
javac 21
Load and use TOOLING script
[JDK tools in jshell ㉑ — JDK-8306560]

What tool would you use
for local prototyping,
testing or debugging a
client-server setup?
34

Introduction to jwebserver
☕ Provides a minimal HTTP server, serving only static files.
☕ Supports only HTTP/1.1 .
☕ Only HEAD and GET requests are served.
☕ Other requests receive a 501 - Not Implemented or a 405 - Not Allowed response.
35
[Introducing jwebserver ⑱ - JEP 408]

# Web development testing, to simulate locally a client-server setup.
$ jwebserver
> Binding to loopback by default. For all interfaces use "-b 0.0.0.0" > or "-b ::".
> Serving /cwd and subdirectories on 127.0.0.1 port 8000
> URL: http://127.0.0.1:8000/
# Use static files as API stubs for web-service prototyping or application testing.
$ jwebserver -p 9000
> Binding to loopback by default. For all interfaces use "-b 0.0.0.0" or "-b ::".
> Serving /example and subdirectories on 127.0.0.1 port 9000
> URL http://127.0.0.1:9000/
> 127.0.0.1 -- [09/Feb/2024:3:02:05 +0200] "GET /api/a1.json HTTP/1.1" 200
> 127.0.0.1 -- [09/Feb/2024:3:02:06 +0200] "GET /api/a2.json HTTP/1.1" 200
Use cases for jwebserver(1)

# Search a directory on a remote server from your local machine.
$ jwebserver -b 0.0.0.0
> Serving /work and subdirectories on 0.0.0.0 (all interfaces) port 8000
> URL http://192.168.178.41:8000/
# Can also be started via java launcher
$ java -m jdk.httpserver
> Binding to loopback by default. For all interfaces use "-b 0.0.0.0" or "-b ::".
> Serving /example and subdirectories on 127.0.0.1 port 8000
> URL http://127.0.0.1:8000/
# Great for learning purposes.
Use cases for jwebserver(2)

The SimpleFileServer class supports the creation of:
☕ file server
☕ file handler
☕ an output filter
$ jshell
jshell> var server = SimpleFileServer.createFileServer(new InetSocketAddress(8080),
...> Path.of("/some/path"), OutputLevel.VERBOSE);
jshell> server.start()
Working with the simple web server API

Packaging self-contained
Java applications
39

Introduction to jpackage
☕ Packages self-contained Java applications.
☕ Prior JDK 19, installing a jpackaged app was system-wide.
☕ For modular applications, jpackage will automatically run jlink and generate a runtime with the
modules needed.
40

jpackage --input target/ --name JDemoApp
--main-jar JDemoApp.jar
--main-class org.example.JDemoApp
--type app-image
Using jpackage
JDemoApp.app/
Contents/
Info.plist
MacOS/ //Application launchers
JDemoApp
Resources/ // Icons, etc.
app/
JDemoApp.cfg //Configuration info, made by jpackage
JDemoApp.jar //JAR file, copied from the --input directory
runtime/ //Java runtime image

# Application launcher will look up the .cfg file in user-specific directories.
Linux
~/.local/${PACKAGE_NAME}
~/.${PACKAGE_NAME}
macOS
~/Library/Application Support/${PACKAGE_NAME}
Windows
%LocalAppData%%PACKAGE_NAME%
%AppData%%PACKAGE_NAME%
# ${PACKAGE_NAME} and %PACKAGE_NAME% refer to jpackaged application name.
Installation of a packaged application after JDK 19

Installation of a jpackaged application after JDK 19
Application launcher will look up the .cfg file:
☕ In user-specific directories.
☕ From the installation directory if .cfg file is not found.
☕ From the application image directory if the application launcher is executed from that location.
43

Security Tools
44

# Since JDK 18, you can check the version of keytool and jarsigner.
$ keytool -help -version
> keytool -version [OPTION]...
> Prints the program version
> Options:
> Use "keytool -?, -h, or --help" for this help message
$ keytool -version & jarsigner -version
> [1] 83711 jarsigner 21 keytool 21
New –version option for keytool and jarsigner
[Add -version option to keytool and jarsigner ⑱ — JDK-8272163]

# keytool warns you when using weak password-based encryption algorithms via -genseckey and -importpass options
$ keytool -genseckey -alias secret -keypass changeit
-keyalg RC4 -keysize 128 -keystore example.p12
-storepass changeit -storetype PKCS12 -v
> Generated 128-bit ARCFOUR secret key [Storing example.p12]
> Warning: The generated secret key uses the ARCFOUR algorithm which is considered a security risk.
Updated options for keytool
[keytool warns about weak PBE algorithms ㉑ — JDK-8286907]

# Specify the classpath for providers via –providerPath
$ jarsigner -keystore keystore -storetype CUSTOMKS
-providerPath /path/to/test.myks
-providerClass my.custom.AnotherProvider
signed.jar mykey
# The options -altsigner and -altsignerpath have been removed in JDK 21.
Updated options for jarsigner
[Add -providerPath option to jarsigner ⑲ — JDK-8281175]

Monitoring Tools
48

Monitoring Java applications
49
Technology Goal
JDK Flight Recorder (JFR) Collects diagnostic and profiling data about a running Java
application.
JFR Event Streaming API API for the continuous consumption of JFR data on disk.
JDK Mission Control (JMC) A set of tools for managing, monitoring, profiling, and
troubleshooting Java applications.

New jfr view command
☕ Displays aggregated event data without the need to dump a recording file.
☕ Start JFR a recording via -XX:StartFlightRecording or jcmd.
$ java -XX:StartFlightRecording -jar imaging.jar
☕ Use the PID or jar name in the command.
☕ Use jps JDK tool to list all running Java processes (PID).
50
[JFR view command ㉑ — JDK-8306704 ]

$ jcmd imaging.jar JFR.view hot-methods
30598:
Java Methods that Execute the Most
Method Samples Percent
--------------------------------------------------------------------- ------- -------
org.springframework.boot.loader.jar.JarFileEntries.sort(int, int) 1 33,33%
jdk.internal.util.ArraysSupport.signedHashCode(int, byte[], int, int) 1 33,33%
java.net.URLStreamHandler.toExternalForm(URL) 1 33,33%
Timespan: 15:46:40 - 15:56:40
JFR view command example

JFR event for finalization - jdk.FinalizerStatistics
☕ Identifies classes at runtime that use finalizers.
☕ No event is sent if java --finalization=disabled.
☕ Enabled by default in default.jfc and profile.jfc JFR configuration files.
☕ Disable via:
$ jfr configure jdk.FinalizerStatistics#enabled=false
# or on launch
$ java -XX:StartFlightRecording:settings=none,+jdk.FinalizerStatistics#enabled=false
52
[A finalization JFR event - JDK-8266936]

Initial security properties -jdk.InitialSecurityProperty
☕ Records initial security properties at application startup.
☕ Enabled by default in default.jfc and profile.jfc JFR configuration files.
☕ Disable via:
$ jfr configure jdk.InitialSecurityProperty#enabled=false
# or on launch
$ java -XX:StartFlightRecording:settings=none,+jdk.InitialSecurityProperty#enabled=false
53

Record details about security provider instance requests
☕ jdk.SecurityProviderService is disabled by default.
☕ Records details about java.security.Provider.getService(String key, String value) calls.
☕ Enable via:
$ jfr configure jdk.SecurityProviderService#enabled=true
# or on launch
$ java -XX:StartFlightRecording:settings=none,+jdk.SecurityProviderService#enabled=true
54

JMC Graph Views for performance analysis
☕ JMC 9 requires JDK 17 or later!
☕ Since JMC 8.3, JMC Graph View was updated to allow limiting the number of nodes displayed.
☕ Focus on most impactful nodes by using smart pruning.
☕ Example : focus on how often a specific method is ran based on sampling.
Open JFR Recording -> Method Profiling -> Select method -> Graph View
55

56

JMC Flame View graphs for performance analysis
☕ Flame View has options that limit the data displayed on the view.
☕ In Samples drop-down, select either Allocation Size, Sample Weight or TLAB Size.
☕ Example use case: visualize where your program is spending its memory.
Open JFR Recording -> Memory-> Flame View
☕ Starting with JMC 9, Flame Graph will now be rendered using Java Swing
57

58

New JMC Dependency View
☕ Shows the relationships between packages within a stack trace.
☕ View dependencies as a chord graph, a circle showing how packages call one another.
☕ A chord graph has thicker lines to represent stronger connections.
☕ Example use case: check dependency view for classes in Memory page.
Open JFR Recording -> Memory-> Select Class -> Dependency View
59

60

Stay tuned for more!
61
Inside.java
Dev.java youtube.com/java

Useful links
☕ Programmer’s Guide to Snippets: https://docs.oracle.com/en/java/javase/21/javadoc/programmers-guide-snippets.html
☕ Java 21 Tool Enhancements: Better Across the Board #RoadTo21 https://www.youtube.com/embed/nFJBVuaIsRg
☕ Using Jshell API https://inside.java/2022/11/21/jshell-java-source-browser/
☕ Christian Stein’s article on jshell tooling https://sormuras.github.io/blog/2023-03-09-jshell-tooling
☕ Julia Boes article on more advanced jwebserver usage https://inside.java/2021/12/06/working-with-the-simple-web-server/
☕ JEP 408 on jwebserver https://openjdk.org/jeps/408
☕ More on jpackage: https://dev.java/learn/jvm/tool/jpackage/
☕ Package a JavaFX application as a native executable https://inside.java/2023/11/14/package-javafx-native-exec/
☕ Stack Walker ep 2 on JFR https://inside.java/2023/05/14/stackwalker-02/
☕ Monitoring Java Application Security with JDK tools and JFR Events: https://dev.java/learn/security/monitor/
☕JEP 467 on markdown documentation cmments: https://openjdk.org/jeps/467
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Enhancing Productivity and Insight A Tour of JDK Tools Progress Beyond Java 17

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