JVM

Find out what classes are loaded by the JVM

  • Use JVM option -verbose:class for java command line

    [0.688s][info][class,load] ch.qos.logback.classic.Logger source: file:/mnt/c/Users/Takechiyo/.m2/repository/ch/qos/logback/logback-classic/1.2.10/logback-classic-1.2.10.jar

  • Use Java API

    • Determine the file containing the class

      var clazz = Logger.class;
var resourceName = clazz.getSimpleName() + ".class";
System.out.println(clazz.getCanonicalName() + ": " + clazz.getResource(resourceName));
 
// ch.qos.logback.classic.Logger: jar:file:/C:/Users/Takechiyo/.m2/repository/ch/qos/logback/logback-classic/1.2.10/logback-classic-1.2.10.jar!/ch/qos/logback/classic/Logger.class

    • Determine the classloader and file containing the class

      private static void examineClass(Class<?> classObject) {
    var fullName = classObject.getName();
    var resourceName = fullName.replaceAll("\\.", "/") + ".class";
    try {
        var clazz = Class.forName(fullName);
        var loader = clazz.getClassLoader();
        System.out.println("Class: " + clazz.getName());
        System.out.println("Loader: " + loader);
 
        var url = ClassLoader.getSystemResource(resourceName);
        System.out.println("Loaded from: " + url);
 
        System.out.println("All locations: ");
        var e = ClassLoader.getSystemResources(resourceName);
        while (e.hasMoreElements()) {
            url = e.nextElement();
            System.out.println("   " + url);
        }
    } catch (Exception e) {
        e.printStackTrace();
    }
}
 
examineClass(ch.qos.logback.classic.Logger.class);
/**
  Class: ch.qos.logback.classic.Logger
  Loader: jdk.internal.loader.ClassLoaders$AppClassLoader@77556fd
  Loaded from: jar:file:/C:/Users/Takechiyo/.m2/repository/ch/qos/logback/logback-classic/1.2.10/logback-classic-1.2.10.jar!/ch/qos/logback/classic/Logger.class
  All locations:
    jar:file:/C:/Users/Takechiyo/.m2/repository/ch/qos/logback/logback-classic/1.2.10/logback-classic-1.2.10.jar!/ch/qos/logback/classic/Logger.class
*/

Classloaders

Fundamental classloaders

  • Primordial/Bootstrap classloader
    • Loads the most fundamental Java library classes
    • Part of JVM
  • Extension/Platform classloader
    • Typical name: sun.misc.Launcher$ExtClassLoader
    • Security extension
  • Application/System classloader
    • Typical name: sun.misc.Launcher$AppClassLoader / jdk.internal.loader.ClassLoaders$AppClassLoader
    • Most widely used
    • Loads classes and JAR files on the classpath

The parent-delegation model

  • Because class loading is always delegated first to the parent of the class loading hierarchy, the most trusted repository (the core API) is checked first, followed by the standard extensions, then the local files that are on the class path. Finally, classes that are located in any repository that your own class loader can access, are accessible. This system prevents code from less-trusted sources from replacing trusted core API classes by assuming the same name as part of the core API.

Notes

  • You can load classes from a directory or JAR file that is not already on the classpath, by creating your own URLClassLoader instance. This is commonly done to load plugins.
  • The second parameter in the call Class.forName(className, true, loader) ensures that the static initialization of the class happens after loading. You definitely want that to happen.
  • Do NOT use the ClassLoader.loadClass method. It does not run the static initializers.
  • The URLClassLoader loads classes from the file system. If you want to load a class from somewhere else, you need to write your own class loader by extending java.lang.ClassLoader and implementing protected Class<?> findClass(String name) throws ClassNotFoundException.
  • When loading classes dynamically from external sources like plugins, we should use the corresponding Classloader to load target classes to ensure the target URL of the class

Code snippets

Get Classpath Resources

ClassLoader.getSystemResources("")?.collect { URL classPath ->
    def list = []
    new File(classPath.toURI()).traverse(type: FileType.FILES) {
        list << it.path
    }
    list
}
private static List<String> getClassPathResources(String fileExtension) {
    try {
        List<Path> classPaths = EnumerationUtils.toList(ClassLoader.getSystemResources("")).stream().map(u -> {
            try {
                return Paths.get(u.toURI());
            } catch (URISyntaxException e) {
                throw new RuntimeException(e);
            }
        }).collect(Collectors.toList());
        return classPaths.stream().flatMap(p -> {
            try {
                return Files.walk(p).filter(d -> Files.isRegularFile(d))
                        .filter(f -> Strings.isNullOrEmpty(fileExtension) || f.toString().endsWith(String.format(".%s", fileExtension)))
                        .map(i -> i.toAbsolutePath().toString());
            } catch (IOException e) {
                throw new RuntimeException(e);
            }
        }).collect(Collectors.toList());
    } catch (IOException e) {
        throw new RuntimeException(e);
    }
}

Bytecode

Determine the version of Java class file

javap -v $class_file | grep version

Bytecode versions matrix

Java SEReleasedMajorSupported majors
1.0.2May 19964545
1.1February 19974545
1.2December 19984645 .. 46
1.3May 20004745 .. 47
1.4February 20024845 .. 48
5.0September 20044945 .. 49
6December 20065045 .. 50
7July 20115145 .. 51
8March 20145245 .. 52
9September 20175345 .. 53
10March 20185445 .. 54
11September 20185545 .. 55
12March 20195645 .. 56
13September 20195745 .. 57
14March 20205845 .. 58
15September 20205945 .. 59
16March 20216045 .. 60
17September 20216145 .. 61
18March 20226245 .. 62
19September 20226345 .. 63
20March 20236445 .. 64
216545 .. 65

List of bytecode instructions

Wikipedia - List of Java bytecode instructions (opens in a new tab)

CLI

jar

List files included in a JAR file

  • jar tf $jar_file
    • The listed file path is the identifier you used to reference the file, and it can be used to extract or update the particular file.

    e.g.

    jar tf playground-spring-boot-cli-0.1-SNAPSHOT.jar | grep properties
90:BOOT-INF/classes/application.properties
95:META-INF/maven/cq-playground/playground-spring-boot-cli/pom.properties

Extract files from a JAR file

  • jar xvf $jar_file

    Extract all files

  • jar xvf $jar_file [$file1, $file2...]

    Extract specified files, note the file name must contain path from within the archive, file name alone is not enough.

    e.g.

    • jar xf playground-spring-boot-cli-0.1-SNAPSHOT.jar BOOT-INF/classes/application.properties

    Note: unzip can also extract files from a JAR file.

Update a file from a JAR file

jar uf $jar_file [$file1, $file2...]

javac

Usage: javac <options> <source files>
where possible options include:
  @<filename>                  Read options and filenames from file
  -Akey[=value]                Options to pass to annotation processors
  --add-modules <module>(,<module>)*
        Root modules to resolve in addition to the initial modules,
        or all modules on the module path if <module> is ALL-MODULE-PATH.
  --boot-class-path <path>, -bootclasspath <path>
        Override location of bootstrap class files
  --class-path <path>, -classpath <path>, -cp <path>
        Specify where to find user class files and annotation processors
  -d <directory>               Specify where to place generated class files
  -deprecation
        Output source locations where deprecated APIs are used
  --enable-preview
        Enable preview language features.
        To be used in conjunction with either -source or --release.
  -encoding <encoding>         Specify character encoding used by source files
  -endorseddirs <dirs>         Override location of endorsed standards path
  -extdirs <dirs>              Override location of installed extensions
  -g                           Generate all debugging info
  -g:{lines,vars,source}       Generate only some debugging info
  -g:none                      Generate no debugging info
  -h <directory>
        Specify where to place generated native header files
  --help, -help, -?            Print this help message
  --help-extra, -X             Print help on extra options
  -implicit:{none,class}
        Specify whether to generate class files for implicitly referenced files
  -J<flag>                     Pass <flag> directly to the runtime system
  --limit-modules <module>(,<module>)*
        Limit the universe of observable modules
  --module <module>(,<module>)*, -m <module>(,<module>)*
        Compile only the specified module(s), check timestamps
  --module-path <path>, -p <path>
        Specify where to find application modules
  --module-source-path <module-source-path>
        Specify where to find input source files for multiple modules
  --module-version <version>
        Specify version of modules that are being compiled
  -nowarn                      Generate no warnings
  -parameters
        Generate metadata for reflection on method parameters
  -proc:{none,only,full}
        Control whether annotation processing and/or compilation is done.
  -processor <class1>[,<class2>,<class3>...]
        Names of the annotation processors to run;
        bypasses default discovery process
  --processor-module-path <path>
        Specify a module path where to find annotation processors
  --processor-path <path>, -processorpath <path>
        Specify where to find annotation processors
  -profile <profile>
        Check that API used is available in the specified profile.
        This option is deprecated and may be removed in a future release.
  --release <release>
        Compile for the specified Java SE release.
        Supported releases:
            8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21
  -s <directory>               Specify where to place generated source files
  --source <release>, -source <release>
        Provide source compatibility with the specified Java SE release.
        Supported releases:
            8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21
  --source-path <path>, -sourcepath <path>
        Specify where to find input source files
  --system <jdk>|none          Override location of system modules
  --target <release>, -target <release>
        Generate class files suitable for the specified Java SE release.
        Supported releases:
            8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21
  --upgrade-module-path <path>
        Override location of upgradeable modules
  -verbose                     Output messages about what the compiler is doing
  --version, -version          Version information
  -Werror                      Terminate compilation if warnings occur

Show all lint keys

javac --help-lint
The supported keys for -Xlint are:
    all                  Enable all warnings
    auxiliaryclass       Warn about an auxiliary class that is hidden in a source file, and is used from other files.
    cast                 Warn about use of unnecessary casts.
    classfile            Warn about issues related to classfile contents.
    deprecation          Warn about use of deprecated items.
    dep-ann              Warn about items marked as deprecated in JavaDoc but not using the @Deprecated annotation.
    divzero              Warn about division by constant integer 0.
    empty                Warn about empty statement after if.
    exports              Warn about issues regarding module exports.
    fallthrough          Warn about falling through from one case of a switch statement to the next.
    finally              Warn about finally clauses that do not terminate normally.
    lossy-conversions    Warn about possible lossy conversions in compound assignment.
    missing-explicit-ctor Warn about missing explicit constructors in public and protected classes in exported packages.
    module               Warn about module system related issues.
    opens                Warn about issues regarding module opens.
    options              Warn about issues relating to use of command line options.
    output-file-clash    Warn when an output file is overwritten during compilation. This can occur, for example,
                         on case-insensitive filesystems. Covers class files, native header files, and source files.
    overloads            Warn about issues regarding method overloads.
    overrides            Warn about issues regarding method overrides.
    path                 Warn about invalid path elements on the command line.
    processing           Warn about issues regarding annotation processing.
    rawtypes             Warn about use of raw types.
    removal              Warn about use of API that has been marked for removal.
    requires-automatic   Warn about use of automatic modules in the requires clauses.
    requires-transitive-automatic Warn about automatic modules in requires transitive.
    serial               Warn about Serializable classes that do not have a serialVersionUID field.
                         Also warn about other suspect declarations in Serializable and Externalizable classes and interfaces.
    static               Warn about accessing a static member using an instance.
    strictfp             Warn about unnecessary use of the strictfp modifier.
    synchronization      Warn about synchronization attempts on instances of value-based classes.
    text-blocks          Warn about inconsistent white space characters in text block indentation.
    this-escape          Warn when a constructor invokes a method that could be overriden in an external subclass.
                         Such a method would execute before the subclass constructor completes its initialization.
    try                  Warn about issues relating to use of try blocks (i.e. try-with-resources).
    unchecked            Warn about unchecked operations.
    varargs              Warn about potentially unsafe vararg methods.
    preview              Warn about use of preview language features.
    none                 Disable all warnings

Can be turned on with javac -Xlint:$key

java

Usage: java [options] <mainclass> [args...]
           (to execute a class)
   or  java [options] -jar <jarfile> [args...]
           (to execute a jar file)
   or  java [options] -m <module>[/<mainclass>] [args...]
       java [options] --module <module>[/<mainclass>] [args...]
           (to execute the main class in a module)
   or  java [options] <sourcefile> [args]
           (to execute a single source-file program)

 Arguments following the main class, source file, -jar <jarfile>,
 -m or --module <module>/<mainclass> are passed as the arguments to
 main class.

 where options include:

    -cp <class search path of directories and zip/jar files>
    -classpath <class search path of directories and zip/jar files>
    --class-path <class search path of directories and zip/jar files>
                  A : separated list of directories, JAR archives,
                  and ZIP archives to search for class files.
    -p <module path>
    --module-path <module path>...
                  A : separated list of elements, each element is a file path
                  to a module or a directory containing modules. Each module is either
                  a modular JAR or an exploded-module directory.
    --upgrade-module-path <module path>...
                  A : separated list of elements, each element is a file path
                  to a module or a directory containing modules to replace
                  upgradeable modules in the runtime image. Each module is either
                  a modular JAR or an exploded-module directory.
    --add-modules <module name>[,<module name>...]
                  root modules to resolve in addition to the initial module.
                  <module name> can also be ALL-DEFAULT, ALL-SYSTEM,
                  ALL-MODULE-PATH.
    --enable-native-access <module name>[,<module name>...]
                  modules that are permitted to perform restricted native operations.
                  <module name> can also be ALL-UNNAMED.
    --list-modules
                  list observable modules and exit
    -d <module name>
    --describe-module <module name>
                  describe a module and exit
    --dry-run     create VM and load main class but do not execute main method.
                  The --dry-run option may be useful for validating the
                  command-line options such as the module system configuration.
    --validate-modules
                  validate all modules and exit
                  The --validate-modules option may be useful for finding
                  conflicts and other errors with modules on the module path.
    -D<name>=<value>
                  set a system property
    -verbose:[class|module|gc|jni]
                  enable verbose output for the given subsystem
    -version      print product version to the error stream and exit
    --version     print product version to the output stream and exit
    -showversion  print product version to the error stream and continue
    --show-version
                  print product version to the output stream and continue
    --show-module-resolution
                  show module resolution output during startup
    -? -h -help
                  print this help message to the error stream
    --help        print this help message to the output stream
    -X            print help on extra options to the error stream
    --help-extra  print help on extra options to the output stream
    -ea[:<packagename>...|:<classname>]
    -enableassertions[:<packagename>...|:<classname>]
                  enable assertions with specified granularity
    -da[:<packagename>...|:<classname>]
    -disableassertions[:<packagename>...|:<classname>]
                  disable assertions with specified granularity
    -esa | -enablesystemassertions
                  enable system assertions
    -dsa | -disablesystemassertions
                  disable system assertions
    -agentlib:<libname>[=<options>]
                  load native agent library <libname>, e.g. -agentlib:jdwp
                  see also -agentlib:jdwp=help
    -agentpath:<pathname>[=<options>]
                  load native agent library by full pathname
    -javaagent:<jarpath>[=<options>]
                  load Java programming language agent, see java.lang.instrument
    -splash:<imagepath>
                  show splash screen with specified image
                  HiDPI scaled images are automatically supported and used
                  if available. The unscaled image filename, e.g. image.ext,
                  should always be passed as the argument to the -splash option.
                  The most appropriate scaled image provided will be picked up
                  automatically.
                  See the SplashScreen API documentation for more information
    @argument files
                  one or more argument files containing options
    --disable-@files
                  prevent further argument file expansion
    --enable-preview
                  allow classes to depend on preview features of this release
To specify an argument for a long option, you can use --<name>=<value> or
--<name> <value>.

java - command reference

Oracle Help Center - Java SE 21 - Tools Reference - The java command (opens in a new tab)

java - VM Options Explorer

VM Options Explorer (opens in a new tab)

java - shows non-standard options

java -X

java - specify system properties

java -D$property_name=$property_value $class_name

Use jcmd $JVM_PID VM.system_properties to verify if a property is effective

java - display system property settings

java -XshowSettings:properties

Output:

Property settings:
    file.encoding = UTF-8
    file.separator = /
    java.class.path =
    java.class.version = 65.0
    java.home = /home/takechiyo/.sdkman/candidates/java/21.0.2-graalce
    java.io.tmpdir = /tmp
    java.library.path = /usr/java/packages/lib
        /usr/lib64
        /lib64
        /lib
        /usr/lib
    java.runtime.name = OpenJDK Runtime Environment
    java.runtime.version = 21.0.2+13-jvmci-23.1-b30
    java.specification.name = Java Platform API Specification
    java.specification.vendor = Oracle Corporation
    java.specification.version = 21
    java.vendor = GraalVM Community
    java.vendor.url = https://www.graalvm.org/
    java.vendor.url.bug = https://github.com/oracle/graal/issues
    java.vendor.version = GraalVM CE 21.0.2+13.1
    java.version = 21.0.2
    java.version.date = 2024-01-16
    java.vm.compressedOopsMode = Zero based
    java.vm.info = mixed mode, sharing
    java.vm.name = OpenJDK 64-Bit Server VM
    java.vm.specification.name = Java Virtual Machine Specification
    java.vm.specification.vendor = Oracle Corporation
    java.vm.specification.version = 21
    java.vm.vendor = GraalVM Community
    java.vm.version = 21.0.2+13-jvmci-23.1-b30
    jdk.debug = release
    jdk.internal.vm.ci.enabled = true
    line.separator = \n
    native.encoding = UTF-8
    os.arch = amd64
    os.name = Linux
    os.version = 6.6.87.2-microsoft-standard-WSL2
    path.separator = :
    stderr.encoding = UTF-8
    stdout.encoding = UTF-8
    sun.arch.data.model = 64
    sun.boot.library.path = /home/takechiyo/.sdkman/candidates/java/21.0.2-graalce/lib
    sun.cpu.endian = little
    sun.io.unicode.encoding = UnicodeLittle
    sun.java.launcher = SUN_STANDARD
    sun.jnu.encoding = UTF-8
    sun.management.compiler = HotSpot 64-Bit Tiered Compilers
    user.country = US
    user.dir = /mnt/c/Users/Takechiyo/workspace
    user.home = /home/takechiyo
    user.language = en
    user.name = takechiyo

java - use @ prefix to reference files containing arguments

Use the @ prefix to identify an argument file that contains java options and class names.

e.g.

java @path1/options @path2/classes

java - debug SSL/TLS Connections

  • Use system property javax.net.debug=ssl, for options check reference below.

    # The current options are:
 
    all: Turn on all debugging
    ssl: Turn on SSL debugging
 
# The following can be used with the ssl option to select what type of debug information to print:
 
    defaultctx: Print default SSL initialization
    handshake: Print each handshake message
    keygen: Print key generation data
    keymanager: Print key manager tracing
    pluggability: Print pluggability tracing
    record: Enable per-record tracing
    respmgr: Print status response manager tracing
    session: Print session activity
    sessioncache: Print session cache tracing
    sslctx: Print SSLContext tracing
    trustmanager: Print trust manager tracing
 
# Messages generated from the handshake option can be widened with these options:
 
    data: Hex dump of each handshake message
    verbose: Verbose handshake message printing
 
# Messages generated from the record option can be widened with these options:
 
    plaintext: Hex dump of record plaintext
    packet: Print raw SSL/TLS packets

  • Resources

java - view security properties, security providers, and TLS-related settings

java -XshowSettings:security

Output:

VM settings:
    Max. Heap Size (Estimated): 3.90G
    Using VM: OpenJDK 64-Bit Server VM

Property settings:
    file.encoding = UTF-8
    file.separator = /
    java.class.path =
    java.class.version = 65.0
    java.home = /home/takechiyo/.sdkman/candidates/java/21.0.2-graalce
    java.io.tmpdir = /tmp
    java.library.path = /usr/java/packages/lib
        /usr/lib64
        /lib64
        /lib
        /usr/lib
    java.runtime.name = OpenJDK Runtime Environment
    java.runtime.version = 21.0.2+13-jvmci-23.1-b30
    java.specification.name = Java Platform API Specification
    java.specification.vendor = Oracle Corporation
    java.specification.version = 21
    java.vendor = GraalVM Community
    java.vendor.url = https://www.graalvm.org/
    java.vendor.url.bug = https://github.com/oracle/graal/issues
    java.vendor.version = GraalVM CE 21.0.2+13.1
    java.version = 21.0.2
    java.version.date = 2024-01-16
    java.vm.compressedOopsMode = Zero based
    java.vm.info = mixed mode, sharing
    java.vm.name = OpenJDK 64-Bit Server VM
    java.vm.specification.name = Java Virtual Machine Specification
    java.vm.specification.vendor = Oracle Corporation
    java.vm.specification.version = 21
    java.vm.vendor = GraalVM Community
    java.vm.version = 21.0.2+13-jvmci-23.1-b30
    jdk.debug = release
    jdk.internal.vm.ci.enabled = true
    line.separator = \n
    native.encoding = UTF-8
    os.arch = amd64
    os.name = Linux
    os.version = 6.6.87.2-microsoft-standard-WSL2
    path.separator = :
    stderr.encoding = UTF-8
    stdout.encoding = UTF-8
    sun.arch.data.model = 64
    sun.boot.library.path = /home/takechiyo/.sdkman/candidates/java/21.0.2-graalce/lib
    sun.cpu.endian = little
    sun.io.unicode.encoding = UnicodeLittle
    sun.java.launcher = SUN_STANDARD
    sun.jnu.encoding = UTF-8
    sun.management.compiler = HotSpot 64-Bit Tiered Compilers
    user.country = US
    user.dir = /mnt/c/Users/Takechiyo/workspace
    user.home = /home/takechiyo
    user.language = en
    user.name = takechiyo

Locale settings:
    default locale = English (United States)
    default display locale = English (United States)
    default format locale = English (United States)
    tzdata version = 2023c
    available locales = , af, af_NA, af_ZA, af_ZA_#Latn, agq, agq_CM, agq_CM_#Latn,
        ak, ak_GH, ak_GH_#Latn, am, am_ET, am_ET_#Ethi, ann, ann_NG,
        ann_NG_#Latn, ar, ar_001, ar_AE, ar_BH, ar_DJ, ar_DZ, ar_EG,
        ar_EG_#Arab, ar_EH, ar_ER, ar_IL, ar_IQ, ar_JO, ar_KM, ar_KW,
        ar_LB, ar_LY, ar_MA, ar_MR, ar_OM, ar_PS, ar_QA, ar_SA,
        ar_SD, ar_SO, ar_SS, ar_SY, ar_TD, ar_TN, ar_YE, as,
        as_IN, as_IN_#Beng, asa, asa_TZ, asa_TZ_#Latn, ast, ast_ES, ast_ES_#Latn,
        az, az_AZ, az_AZ_#Cyrl, az_AZ_#Latn, az__#Cyrl, az__#Latn, bas, bas_CM,
        bas_CM_#Latn, be, be_BY, be_BY_#Cyrl, be__TARASK, bem, bem_ZM, bem_ZM_#Latn,
        bez, bez_TZ, bez_TZ_#Latn, bg, bg_BG, bg_BG_#Cyrl, bgc, bgc_IN,
        bgc_IN_#Deva, bho, bho_IN, bho_IN_#Deva, bm, bm_ML, bm_ML_#Latn, bn,
        bn_BD, bn_BD_#Beng, bn_IN, bo, bo_CN, bo_CN_#Tibt, bo_IN, br,
        br_FR, br_FR_#Latn, brx, brx_IN, brx_IN_#Deva, bs, bs_BA, bs_BA_#Cyrl,
        bs_BA_#Latn, bs__#Cyrl, bs__#Latn, ca, ca_AD, ca_ES, ca_ES_#Latn, ca_ES_VALENCIA,
        ca_FR, ca_IT, ccp, ccp_BD, ccp_BD_#Cakm, ccp_IN, ce, ce_RU,
        ce_RU_#Cyrl, ceb, ceb_PH, ceb_PH_#Latn, cgg, cgg_UG, cgg_UG_#Latn, chr,
        chr_US, chr_US_#Cher, ckb, ckb_IQ, ckb_IQ_#Arab, ckb_IR, cs, cs_CZ,
        cs_CZ_#Latn, cv, cv_RU, cv_RU_#Cyrl, cy, cy_GB, cy_GB_#Latn, da,
        da_DK, da_DK_#Latn, da_GL, dav, dav_KE, dav_KE_#Latn, de, de_AT,
        de_BE, de_CH, de_DE, de_DE_#Latn, de_IT, de_LI, de_LU, dje,
        dje_NE, dje_NE_#Latn, doi, doi_IN, doi_IN_#Deva, dsb, dsb_DE, dsb_DE_#Latn,
        dua, dua_CM, dua_CM_#Latn, dyo, dyo_SN, dyo_SN_#Latn, dz, dz_BT,
        dz_BT_#Tibt, ebu, ebu_KE, ebu_KE_#Latn, ee, ee_GH, ee_GH_#Latn, ee_TG,
        el, el_CY, el_GR, el_GR_#Grek, el__POLYTON, en, en_001, en_150,
        en_AE, en_AG, en_AI, en_AS, en_AT, en_AU, en_BB, en_BE,
        en_BI, en_BM, en_BS, en_BW, en_BZ, en_CA, en_CC, en_CH,
        en_CK, en_CM, en_CX, en_CY, en_DE, en_DG, en_DK, en_DM,
        en_ER, en_FI, en_FJ, en_FK, en_FM, en_GB, en_GD, en_GG,
        en_GH, en_GI, en_GM, en_GU, en_GY, en_HK, en_IE, en_IL,
        en_IM, en_IN, en_IO, en_JE, en_JM, en_KE, en_KI, en_KN,
        en_KY, en_LC, en_LR, en_LS, en_MG, en_MH, en_MO, en_MP,
        en_MS, en_MT, en_MU, en_MV, en_MW, en_MY, en_NA, en_NF,
        en_NG, en_NL, en_NR, en_NU, en_NZ, en_PG, en_PH, en_PK,
        en_PN, en_PR, en_PW, en_RW, en_SB, en_SC, en_SD, en_SE,
        en_SG, en_SH, en_SI, en_SL, en_SS, en_SX, en_SZ, en_TC,
        en_TK, en_TO, en_TT, en_TV, en_TZ, en_UG, en_UM, en_US,
        en_US_#Latn, en_US_POSIX, en_VC, en_VG, en_VI, en_VU, en_WS, en_ZA,
        en_ZM, en_ZW, eo, eo_001, eo_001_#Latn, es, es_419, es_AR,
        es_BO, es_BR, es_BZ, es_CL, es_CO, es_CR, es_CU, es_DO,
        es_EA, es_EC, es_ES, es_ES_#Latn, es_GQ, es_GT, es_HN, es_IC,
        es_MX, es_NI, es_PA, es_PE, es_PH, es_PR, es_PY, es_SV,
        es_US, es_UY, es_VE, et, et_EE, et_EE_#Latn, eu, eu_ES,
        eu_ES_#Latn, ewo, ewo_CM, ewo_CM_#Latn, fa, fa_AF, fa_IR, fa_IR_#Arab,
        ff, ff_BF_#Adlm, ff_BF_#Latn, ff_CM_#Adlm, ff_CM_#Latn, ff_GH_#Adlm, ff_GH_#Latn, ff_GM_#Adlm,
        ff_GM_#Latn, ff_GN, ff_GN_#Adlm, ff_GN_#Latn, ff_GW_#Adlm, ff_GW_#Latn, ff_LR_#Adlm, ff_LR_#Latn,
        ff_MR_#Adlm, ff_MR_#Latn, ff_NE_#Adlm, ff_NE_#Latn, ff_NG_#Adlm, ff_NG_#Latn, ff_SL_#Adlm, ff_SL_#Latn,
        ff_SN, ff_SN_#Adlm, ff_SN_#Latn, ff__#Adlm, ff__#Latn, fi, fi_FI, fi_FI_#Latn,
        fil, fil_PH, fil_PH_#Latn, fo, fo_DK, fo_FO, fo_FO_#Latn, fr,
        fr_BE, fr_BF, fr_BI, fr_BJ, fr_BL, fr_CA, fr_CD, fr_CF,
        fr_CG, fr_CH, fr_CI, fr_CM, fr_DJ, fr_DZ, fr_FR, fr_FR_#Latn,
        fr_GA, fr_GF, fr_GN, fr_GP, fr_GQ, fr_HT, fr_KM, fr_LU,
        fr_MA, fr_MC, fr_MF, fr_MG, fr_ML, fr_MQ, fr_MR, fr_MU,
        fr_NC, fr_NE, fr_PF, fr_PM, fr_RE, fr_RW, fr_SC, fr_SN,
        fr_SY, fr_TD, fr_TG, fr_TN, fr_VU, fr_WF, fr_YT, frr,
        frr_DE, frr_DE_#Latn, fur, fur_IT, fur_IT_#Latn, fy, fy_NL, fy_NL_#Latn,
        ga, ga_GB, ga_IE, ga_IE_#Latn, gd, gd_GB, gd_GB_#Latn, gl,
        gl_ES, gl_ES_#Latn, gsw, gsw_CH, gsw_CH_#Latn, gsw_FR, gsw_LI, gu,
        gu_IN, gu_IN_#Gujr, guz, guz_KE, guz_KE_#Latn, gv, gv_IM, gv_IM_#Latn,
        ha, ha_GH, ha_NE, ha_NG, ha_NG_#Latn, haw, haw_US, haw_US_#Latn,
        he, he_IL, he_IL_#Hebr, hi, hi_IN, hi_IN_#Deva, hi_IN_#Latn, hi__#Latn,
        hr, hr_BA, hr_HR, hr_HR_#Latn, hsb, hsb_DE, hsb_DE_#Latn, hu,
        hu_HU, hu_HU_#Latn, hy, hy_AM, hy_AM_#Armn, ia, ia_001, ia_001_#Latn,
        id, id_ID, id_ID_#Latn, ig, ig_NG, ig_NG_#Latn, ii, ii_CN,
        ii_CN_#Yiii, is, is_IS, is_IS_#Latn, it, it_CH, it_IT, it_IT_#Latn,
        it_SM, it_VA, ja, ja_JP, ja_JP_#Jpan, ja_JP_JP_#u-ca-japanese, jgo, jgo_CM,
        jgo_CM_#Latn, jmc, jmc_TZ, jmc_TZ_#Latn, jv, jv_ID, jv_ID_#Latn, ka,
        ka_GE, ka_GE_#Geor, kab, kab_DZ, kab_DZ_#Latn, kam, kam_KE, kam_KE_#Latn,
        kde, kde_TZ, kde_TZ_#Latn, kea, kea_CV, kea_CV_#Latn, kgp, kgp_BR,
        kgp_BR_#Latn, khq, khq_ML, khq_ML_#Latn, ki, ki_KE, ki_KE_#Latn, kk,
        kk_KZ, kk_KZ_#Cyrl, kkj, kkj_CM, kkj_CM_#Latn, kl, kl_GL, kl_GL_#Latn,
        kln, kln_KE, kln_KE_#Latn, km, km_KH, km_KH_#Khmr, kn, kn_IN,
        kn_IN_#Knda, ko, ko_KP, ko_KR, ko_KR_#Kore, kok, kok_IN, kok_IN_#Deva,
        ks, ks_IN, ks_IN_#Arab, ks_IN_#Deva, ks__#Arab, ks__#Deva, ksb, ksb_TZ,
        ksb_TZ_#Latn, ksf, ksf_CM, ksf_CM_#Latn, ksh, ksh_DE, ksh_DE_#Latn, ku,
        ku_TR, ku_TR_#Latn, kw, kw_GB, kw_GB_#Latn, ky, ky_KG, ky_KG_#Cyrl,
        lag, lag_TZ, lag_TZ_#Latn, lb, lb_LU, lb_LU_#Latn, lg, lg_UG,
        lg_UG_#Latn, lkt, lkt_US, lkt_US_#Latn, ln, ln_AO, ln_CD, ln_CD_#Latn,
        ln_CF, ln_CG, lo, lo_LA, lo_LA_#Laoo, lrc, lrc_IQ, lrc_IR,
        lrc_IR_#Arab, lt, lt_LT, lt_LT_#Latn, lu, lu_CD, lu_CD_#Latn, luo,
        luo_KE, luo_KE_#Latn, luy, luy_KE, luy_KE_#Latn, lv, lv_LV, lv_LV_#Latn,
        mai, mai_IN, mai_IN_#Deva, mas, mas_KE, mas_KE_#Latn, mas_TZ, mdf,
        mdf_RU, mdf_RU_#Cyrl, mer, mer_KE, mer_KE_#Latn, mfe, mfe_MU, mfe_MU_#Latn,
        mg, mg_MG, mg_MG_#Latn, mgh, mgh_MZ, mgh_MZ_#Latn, mgo, mgo_CM,
        mgo_CM_#Latn, mi, mi_NZ, mi_NZ_#Latn, mk, mk_MK, mk_MK_#Cyrl, ml,
        ml_IN, ml_IN_#Mlym, mn, mn_MN, mn_MN_#Cyrl, mni, mni_IN, mni_IN_#Beng,
        mni__#Beng, mr, mr_IN, mr_IN_#Deva, ms, ms_BN, ms_ID, ms_MY,
        ms_MY_#Latn, ms_SG, mt, mt_MT, mt_MT_#Latn, mua, mua_CM, mua_CM_#Latn,
        my, my_MM, my_MM_#Mymr, mzn, mzn_IR, mzn_IR_#Arab, naq, naq_NA,
        naq_NA_#Latn, nb, nb_NO, nb_NO_#Latn, nb_SJ, nd, nd_ZW, nd_ZW_#Latn,
        nds, nds_DE, nds_DE_#Latn, nds_NL, ne, ne_IN, ne_NP, ne_NP_#Deva,
        nl, nl_AW, nl_BE, nl_BQ, nl_CW, nl_NL, nl_NL_#Latn, nl_SR,
        nl_SX, nmg, nmg_CM, nmg_CM_#Latn, nn, nn_NO, nn_NO_#Latn, nnh,
        nnh_CM, nnh_CM_#Latn, no, no_NO, no_NO_#Latn, no_NO_NY, nus, nus_SS,
        nus_SS_#Latn, nyn, nyn_UG, nyn_UG_#Latn, oc, oc_ES, oc_FR, oc_FR_#Latn,
        om, om_ET, om_ET_#Latn, om_KE, or, or_IN, or_IN_#Orya, os,
        os_GE, os_GE_#Cyrl, os_RU, pa, pa_IN, pa_IN_#Guru, pa_PK, pa_PK_#Arab,
        pa__#Arab, pa__#Guru, pcm, pcm_NG, pcm_NG_#Latn, pis, pis_SB, pis_SB_#Latn,
        pl, pl_PL, pl_PL_#Latn, ps, ps_AF, ps_AF_#Arab, ps_PK, pt,
        pt_AO, pt_BR, pt_BR_#Latn, pt_CH, pt_CV, pt_GQ, pt_GW, pt_LU,
        pt_MO, pt_MZ, pt_PT, pt_ST, pt_TL, qu, qu_BO, qu_EC,
        qu_PE, qu_PE_#Latn, raj, raj_IN, raj_IN_#Deva, rm, rm_CH, rm_CH_#Latn,
        rn, rn_BI, rn_BI_#Latn, ro, ro_MD, ro_RO, ro_RO_#Latn, rof,
        rof_TZ, rof_TZ_#Latn, ru, ru_BY, ru_KG, ru_KZ, ru_MD, ru_RU,
        ru_RU_#Cyrl, ru_UA, rw, rw_RW, rw_RW_#Latn, rwk, rwk_TZ, rwk_TZ_#Latn,
        sa, sa_IN, sa_IN_#Deva, sah, sah_RU, sah_RU_#Cyrl, saq, saq_KE,
        saq_KE_#Latn, sat, sat_IN, sat_IN_#Olck, sat__#Olck, sbp, sbp_TZ, sbp_TZ_#Latn,
        sc, sc_IT, sc_IT_#Latn, sd, sd_IN, sd_IN_#Deva, sd_PK, sd_PK_#Arab,
        sd__#Arab, sd__#Deva, se, se_FI, se_NO, se_NO_#Latn, se_SE, seh,
        seh_MZ, seh_MZ_#Latn, ses, ses_ML, ses_ML_#Latn, sg, sg_CF, sg_CF_#Latn,
        shi, shi_MA, shi_MA_#Latn, shi_MA_#Tfng, shi__#Latn, shi__#Tfng, si, si_LK,
        si_LK_#Sinh, sk, sk_SK, sk_SK_#Latn, sl, sl_SI, sl_SI_#Latn, smn,
        smn_FI, smn_FI_#Latn, sms, sms_FI, sms_FI_#Latn, sn, sn_ZW, sn_ZW_#Latn,
        so, so_DJ, so_ET, so_KE, so_SO, so_SO_#Latn, sq, sq_AL,
        sq_AL_#Latn, sq_MK, sq_XK, sr, sr_BA, sr_BA_#Cyrl, sr_BA_#Latn, sr_CS,
        sr_ME, sr_ME_#Cyrl, sr_ME_#Latn, sr_RS, sr_RS_#Cyrl, sr_RS_#Latn, sr_XK_#Cyrl, sr_XK_#Latn,
        sr__#Cyrl, sr__#Latn, su, su_ID, su_ID_#Latn, su__#Latn, sv, sv_AX,
        sv_FI, sv_SE, sv_SE_#Latn, sw, sw_CD, sw_KE, sw_TZ, sw_TZ_#Latn,
        sw_UG, ta, ta_IN, ta_IN_#Taml, ta_LK, ta_MY, ta_SG, te,
        te_IN, te_IN_#Telu, teo, teo_KE, teo_UG, teo_UG_#Latn, tg, tg_TJ,
        tg_TJ_#Cyrl, th, th_TH, th_TH_#Thai, th_TH_TH_#u-nu-thai, ti, ti_ER, ti_ET,
        ti_ET_#Ethi, tk, tk_TM, tk_TM_#Latn, to, to_TO, to_TO_#Latn, tok,
        tok_001, tok_001_#Latn, tr, tr_CY, tr_TR, tr_TR_#Latn, tt, tt_RU,
        tt_RU_#Cyrl, twq, twq_NE, twq_NE_#Latn, tzm, tzm_MA, tzm_MA_#Latn, ug,
        ug_CN, ug_CN_#Arab, uk, uk_UA, uk_UA_#Cyrl, ur, ur_IN, ur_PK,
        ur_PK_#Arab, uz, uz_AF, uz_AF_#Arab, uz_UZ, uz_UZ_#Cyrl, uz_UZ_#Latn, uz__#Arab,
        uz__#Cyrl, uz__#Latn, vai, vai_LR, vai_LR_#Latn, vai_LR_#Vaii, vai__#Latn, vai__#Vaii,
        vi, vi_VN, vi_VN_#Latn, vun, vun_TZ, vun_TZ_#Latn, wae, wae_CH,
        wae_CH_#Latn, wo, wo_SN, wo_SN_#Latn, xh, xh_ZA, xh_ZA_#Latn, xog,
        xog_UG, xog_UG_#Latn, yav, yav_CM, yav_CM_#Latn, yi, yi_001, yi_001_#Hebr,
        yo, yo_BJ, yo_NG, yo_NG_#Latn, yrl, yrl_BR, yrl_BR_#Latn, yrl_CO,
        yrl_VE, yue, yue_CN, yue_CN_#Hans, yue_HK, yue_HK_#Hant, yue__#Hans, yue__#Hant,
        zgh, zgh_MA, zgh_MA_#Tfng, zh, zh_CN, zh_CN_#Hans, zh_HK, zh_HK_#Hans,
        zh_HK_#Hant, zh_MO, zh_MO_#Hans, zh_MO_#Hant, zh_SG, zh_SG_#Hans, zh_TW, zh_TW_#Hant,
        zh__#Hans, zh__#Hant, zu, zu_ZA, zu_ZA_#Latn
Operating System Metrics:
    Provider: cgroupv2
    Effective CPU Count: 16
    CPU Period: -1
    CPU Quota: -1
    CPU Shares: -1
    List of Processors: N/A
    List of Effective Processors, 16 total:
    0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15
    List of Memory Nodes: N/A
    List of Available Memory Nodes, 1 total:
    0
    Memory Limit: Unlimited
    Memory Soft Limit: Unlimited
    Memory & Swap Limit: Unlimited
    Maximum Processes Limit: Unlimited

java - list security debugging options

java -Djava.security.debug=help

java - apply additional JVM options via JDK_JAVA_OPTIONS and JAVA_TOOL_OPTIONS

JDK_JAVA_OPTIONS

  • Only works for Java 9+ and the java CLI

JAVA_TOOL_OPTIONS

  • In addition to java, also works for other Java tools such as jar and javac
# Set environment variable
export JDK_JAVA_OPTIONS="-Dspring.profiles.active=dev"
 
# Run JVM process
mvn spring-boot:run
 
# A message will display as confirmation
NOTE: Picked up JDK_JAVA_OPTIONS: -Dspring.profiles.active=dev

Caveat: JAVA_OPTS is not standard and not guaranteed to work.

JVM Options - GC

JVM Options - Logging

JVM Options - Memory Settings

  • Heap

    • -Xms is equivalent to -XX:InitialHeapSize.

    • -Xmx is equivalent to -XX:MaxHeapSize.

    • -Xmx should be between 80% and 100% of the machine's physical memory. If you set -Xmx too small, the application server may fail with an OutOfMemory error. If you set -Xmx too large, the memory's footprint is larger and you run the risk of Java's heap being swapped out, causing other performance problems.

    • -Xms should be approximately half of the -Xmx setting. If you have historical data about your application server's stable memory-usage point, then set -Xms to be around that value.

  • Metaspace (formely PermGen)

    • -XX:MaxMetaspaceSize is the maximum amount of native memory that can be allocated for class metadata. The default value depends on the platform.

    • -XX:MetaspaceSize is the initial amount of native memory that can be allocated for class metadata. The default size of is platform-dependent and ranges from 12 MB to about 20 MB.

    • -XX:MaxMetaspaceFreeRatio is the maximum percentage of class metadata free space to class metadata used space after a garbage collection. The default value is 70.

    • -XX:MinMetaspaceFreeRatio is the minimum percentage of class metadata free space to class metadata used space after a garbage collection. The default value is 40.

    • If you observe classes being unloaded during full garbage collections, you should use -XX:PermSize and -XX:MaxPermSize command line options to size the permanent generation space. To avoid full garbage collections that may expand or shrink the committed size of the permanent generation space, set -XX:PermSize and -XX:MaxPermSize to the same value.

    • Resources

JVM Options - Compiler (JIT)

  • -XX:+PrintCompilation prints a message to the console when a method is compiled.
  • -XX:+PrintCompilation2 prints a message to the console when a method is compiled, and includes the time it took to compile the method.

JVM Options - Performance - based on JMC Automated Analysis Results

  • Java Application

    • Memory

      • Free Physical Memory

        Having little free memory may lead to swapping, which is very expensive. To avoid this, either decrease the memory usage or increase the amount of available memory.

    • Exceptions

      • Thrown Errors

        Investigate the thrown errors to see if they can be avoided. Errors indicate that something went wrong with the code execution and should never be used for flow control.

  • JVM Internals

    • Stackdepth Setting

      Some stack traces were truncated in this recording. If more detailed traces are required, increase the -XX:FlightRecorderOptions=stackdepth=<value> value.

    • GC Configuration

      • Compressed Oops

        Not using Compressed Ordinary Object Pointers when the heap size is below 32 GB wastes memory and will lead to unnecessary cache pressure. Use the JVM argument -XX:+UseCompressedOops to enable this feature.

        Refer to OpenJDK Wiki - CompressedOops (opens in a new tab) for details.

  • Environment

    • Processes

      • Competing Processes

        If this is a server environment, it may be good to only run other critical processes on that machine.

JVM Options - Resources

jps

jps - Get arguments of a running JVM process

jps - List all local JVM processes with VM options

jps -lvm

Output (example):

2589 cq.playground.spring.microservice.rest.MainApplication --spring.profiles.active=dev,logging --logging.level.web=debug -XX:ThreadPriorityPolicy=1 -XX:+UnlockExperimentalVMOptions -XX:+EnableJVMCIProduct -XX:-UnlockExperimentalVMOptions -javaagent:/mnt/c/Users/Takechiyo/workspace/gitlab/spring-microservice/deployment/opentelemetry/opentelemetry-javaagent.jar -XX:TieredStopAtLevel=1 -Duser.dir=/mnt/c/Users/Takechiyo/workspace/gitlab/spring-microservice -XX:+UseZGC -XX:+ZGenerational -XX:InitialHeapSize=2g -XX:MaxHeapSize=2g -Xlog:gc*=info,gc+heap=debug,gc+ref*=debug,gc+ergo*=trace,gc+age*=trace:file=/mnt/c/Users/Takechiyo/workspace/gitlab/spring-microservice/target/gc-%t.log:utctime,pid,level,tags:filecount=2,filesize=100m -XX:StartFlightRecording=settings=default,filename=/mnt/c/Users/Takechiyo/workspace/gitlab/spring-microservice/target/spring-microservice.jfr,dumponexit=true,maxsize=100M -XX:+UnlockDiagnosticVMOptions -XX:+LogVMOutput -XX:LogFile=/mnt/c/Users/Takechiyo/workspace/gitlab/spring-microservice/target/jvm.log -XX:ErrorFile=/mnt/c/Users/Takechiyo/workspace/gitlab/spring-microservice/target/hs_err_%p.log -XX:+Disabl

jcmd

  • GC.class_stats command requires -XX:+UnlockDiagnosticVMOptions
Usage: jcmd <pid | main class> <command ...|PerfCounter.print|-f file>
   or: jcmd -l
   or: jcmd -h

  command must be a valid jcmd command for the selected jvm.
  Use the command "help" to see which commands are available.
  If the pid is 0, commands will be sent to all Java processes.
  The main class argument will be used to match (either partially
  or fully) the class used to start Java.
  If no options are given, lists Java processes (same as -l).

  PerfCounter.print display the counters exposed by this process
  -f  read and execute commands from the file
  -l  list JVM processes on the local machine
  -? -h --help print this help message

jcmd - List all local JVM processes

jcmd / jcmd -l
# e.g.
$ jcmd
3157 org.gradle.launcher.GradleMain bootRun
2710 org.gradle.launcher.daemon.bootstrap.GradleDaemon 8.5
5145 jdk.jcmd/sun.tools.jcmd.JCmd
3390 cq.playground.spring.poc.kafka.nonreactive.MainApp

jcmd - List all diagnostic commands for a specific process

jcmd $PID [help]

If PID is 0, the command is sent to all JVM processes

# e.g.
$ jcmd 3390
3390:
The following commands are available:
Compiler.CodeHeap_Analytics
Compiler.codecache
Compiler.codelist
Compiler.directives_add
Compiler.directives_clear
Compiler.directives_print
Compiler.directives_remove
Compiler.perfmap
Compiler.queue
GC.class_histogram
GC.finalizer_info
GC.heap_dump
GC.heap_info
GC.run
GC.run_finalization
JFR.check
JFR.configure
JFR.dump
JFR.start
JFR.stop
JFR.view
JVMTI.agent_load
JVMTI.data_dump
ManagementAgent.start
ManagementAgent.start_local
ManagementAgent.status
ManagementAgent.stop
System.native_heap_info
System.trim_native_heap
Thread.dump_to_file
Thread.print
VM.cds
VM.class_hierarchy
VM.classes
VM.classloader_stats
VM.classloaders
VM.command_line
VM.dynlibs
VM.events
VM.flags
VM.info
VM.log
VM.metaspace
VM.native_memory
VM.set_flag
VM.stringtable
VM.symboltable
VM.system_properties
VM.systemdictionary
VM.uptime
VM.version
help

jcmd - Help for a specific diagnostic command

jcmd $PID/$Main_Class help $command

eg: jcmd 38388 help VM.version

jcmd - List system properties of a JVM process

jcmd $PID VM.system_properties | sort
# e.g.
$ jcmd 3390 VM.system_properties
3390:
#Sun Feb 04 15:06:55 AEDT 2024
CONSOLE_LOG_CHARSET=UTF-8
FILE_LOG_CHARSET=UTF-8
LOG_FILE=/tmp/spring.log
LOG_PATH=/tmp
PID=3390
catalina.base=/tmp/tomcat.8080.470854316564232780
catalina.home=/tmp/tomcat.8080.470854316564232780
catalina.useNaming=false
file.encoding=UTF-8
file.separator=/
java.awt.headless=true

jcmd - List JVM flags

jcmd $PID VM.flags | tr " " "\n" | sort

or

jinfo -flags $PID | tr " " "\n" | sort

jcmd - Show JMX

jinfo

jinfo - List system properties of a JVM process

jinfo -sysprops $PID | sort

jinfo - Print the value of the specified VM flag

jinfo -flag $name

jinfo - Enable/Disable the specified VM flag

jinfo -flag [+|-]$name

jshell

JMX (Java Management Extension)

com.sun.management.jmxremote.ssl = true [default]
com.sun.management.config.file = management.properties [default]
com.sun.management.jmxremote.local.only = true [default]
com.sun.management.jmxremote.access.file = jmxremote.access [default]
com.sun.management.jmxremote.port = 0 [default]
com.sun.management.jmxremote.registry.ssl = false [default]
com.sun.management.jmxremote.authenticate = true [default]
com.sun.management.jmxremote.ssl.need.client.auth = false [default]
com.sun.management.jmxremote.password.file = jmxremote.password [default]

JDP

GUI

JMC (JDK Mission Control)

JMC - Source Code (opens in a new tab)

JMC - JDK Mission Control (opens in a new tab)

jol (Java Object Layout)

VisualVM

References

Reference - Bytecode

Reference - JVM

Reference - JEP

OpenJ9

JFR (Java Flight Recorder)Groovy notes