Forem: Clayton Walker

Snippet: How to handle non-issue (client) exceptions in spring boot

Clayton Walker — Fri, 29 Aug 2025 17:59:25 +0000

If you find yourself writing your own exception handlers, you might have also found yourself manually filtering out 'known-good' exceptions, such as exceptions caused by clients disconnection.

No sense in replicating spring's existing filter, just use DisconnectedClientHelper.isClientDisconnectedException) in your @ControllerAdvice or @ExceptionHandler.

@ControllerAdvice
public class GlobalExceptionHandler {
    @ExceptionHandler
    public ResponseEntity<?> handle(Exception e, WebRequest request) {
        if (DisconnectedClientHelper.isClientDisconnectedException(e)) {
            // handle as usual
            return null;
        }
        // handle other exceptions
        return ResponseEntity.status(HttpStatus.INTERNAL_SERVER_ERROR).build();
    }
}

Bazel issues I'm following

Clayton Walker — Wed, 13 Aug 2025 17:32:02 +0000

In rules_kotlin, you can't use

kotlin 2.2 (yet) https://github.com/bazelbuild/rules_kotlin/pull/1341
runfiles (yet) https://github.com/bazelbuild/rules_kotlin/issues/1095
on windows (yet)
env support (yet) see https://bazel.build/reference/be/common-definitions#binary.env https://github.com/bazelbuild/rules_kotlin/issues/1359
test_env support (fixed) https://github.com/bazelbuild/rules_kotlin/issues/815 but not closed https://github.com/bazelbuild/rules_kotlin/pull/837 ???

Twice now I've had no idea as to why it's giving me a random java error.
This is caused by executing a kotlin binary on java 25

Error occurred during initialization of VM
java.lang.Error: A command line option has attempted to allow or enable the Security Manager. Enabling a Security Manager is not supported.
    at java.lang.System.initPhase3(java.base@25/System.java:1969)

Running c/c++ on the JVM

Clayton Walker — Sat, 14 Jun 2025 18:10:18 +0000

This isn't so much a deep dive as it is a solution in search of a problem.

How to compile to llvm bitcode (or webasm)

Notes: Graalvm supports llvm-bitcode and wasm (https://github.com/oracle/graal/blob/master/wasm/README.md)

How to exclude classes from jacoco in Gradle

Clayton Walker — Thu, 17 Apr 2025 03:26:46 +0000

Basically the only way to re-route is to re-build the JacocoReportBase.classDirectories object from scratch.

tasks.withType<JacocoReportBase>().configureEach {
    classDirectories.setFrom(sourceSets.main.map {
        it.output.asFileTree.matching {
            exclude("**/build/**")
        }
    })
}

reporting {
    reports {
        withType<JacocoCoverageReport>().configureEach {
            reportTask.configure {
                classDirectories.setFrom(sourceSets.main.map {
                    it.output.asFileTree.matching {
                        exclude("**/build/**")
                    }
                })
            }
        }
    }
}

when using the reporting extension.

Follow https://github.com/gradle/gradle/issues/14760 for future updates.

Managing Java installations on macOS

Clayton Walker — Wed, 12 Feb 2025 17:31:10 +0000

By default, macOS ships with a tool to resolve Java installations.

/usr/libexec/java_home

It searches in the following directories:

/Library/Java/JavaVirtualMachines/
~/Library/Java/JavaVirtualMachines/

Intellij will install downloaded jvms into the user's home directory, meaning we can use Intellij to manage and update our java installations. https://www.jetbrains.com/guide/java/tips/download-jdk/

By setting either JAVA_VERSION or JAVA_HOME, calling java will point to the particular java version selected.

cwalker ~ % export JAVA_VERSION=21
cwalker ~ % java --version
openjdk 21.0.6 2025-01-21 LTS
OpenJDK Runtime Environment Corretto-21.0.6.7.1 (build 21.0.6+7-LTS)
OpenJDK 64-Bit Server VM Corretto-21.0.6.7.1 (build 21.0.6+7-LTS, mixed mode, sharing)

For a faster way of switching in a shell, see this answer on stack overflow. https://stackoverflow.com/a/40754792

Fix dynamic agent loading warning in Gradle

Clayton Walker — Sat, 13 Jan 2024 00:32:22 +0000

In newer versions java, dynamically loaded agents will be disallowed. Warnings like the following would be logged by your test runner.

WARNING: A Java agent has been loaded dynamically (/Users/cwalker/.gradle/caches/modules-2/files-2.1/net.bytebuddy/byte-buddy-agent/1.14.6/46e2545d7a97b6ccb195621650c5957279eb4812/byte-buddy-agent-1.14.6.jar)
WARNING: If a serviceability tool is in use, please run with -XX:+EnableDynamicAgentLoading to hide this warning
WARNING: If a serviceability tool is not in use, please run with -Djdk.instrument.traceUsage for more information
WARNING: Dynamic loading of agents will be disallowed by default in a future release

To fix this, we can get add a new agent configuration and map dependencies from that configuration to the -javaagent flag.

Using the new test-suites plugin, that would look like the following.

val testAgent by configurations.creating

dependencies {
    testAgent("net.bytebuddy:byte-buddy-agent:1.14.6")
}

// if configuring test task directly
tasks.test {
    jvmArgumentProviders.add(
        objects.newInstance<JavaAgentArgumentProvider>().apply {
            classpath.from(testAgent)
        }
    )
}

// if using test suites
testing.suites {
    val test by existing(JvmTestSuite::class) {
        targets.configureEach {
            testTask.configure {
                jvmArgumentProviders.add(
                    objects.newInstance<JavaAgentArgumentProvider>().apply {
                        classpath.from(testAgent)
                    }
                )
            }
        }
    }
}

abstract class JavaAgentArgumentProvider : CommandLineArgumentProvider {
    @get:Classpath
    abstract val classpath: ConfigurableFileCollection

    override fun asArguments() = classpath.files.map { "-javaagent:${it.absolutePath}" }
}

Follow the upstream issue for updates.

For simplicity, it may be easier to depend on a third-party dependency (such as javaagent-gradle-plugin) to handle agents.

EDIT 3/2/2025:
Added test.task option
Replaced direct jvmArgs with jvmArgumentProviders to avoid configuration errors on older versions of Gradle 8
EDIT 6/14/2025:
Added support for task relocatability by using a command-line configurator like in this comment https://github.com/mockito/mockito/issues/3037#issuecomment-2724136224 or this plugin https://github.com/bakdata/gradle-plugins/pull/63/files
Added link to ryandens' javaagent-gradle-plugin

Python and distroless: A simplified guide

Clayton Walker — Thu, 12 Oct 2023 01:07:32 +0000

While this guide's focus is on python, the general advice here applies to anyone trying to build docker images on top of distroless base images.

No dependencies

If you have a simple python script with no dependencies, you can follow this guide, whose Dockerfile is reproduced below.

FROM python:3-slim AS build-env
COPY . /app
WORKDIR /app

FROM gcr.io/distroless/python3
COPY --from=build-env /app /app
WORKDIR /app
CMD ["hello.py", "/etc"]

Pure-python dependencies

If you have a requirements.txt but no additional native dependencies you can follow this guide

# Build a virtualenv using the appropriate Debian release
# * Install python3-venv for the built-in Python3 venv module (not installed by default)
# * Install gcc libpython3-dev to compile C Python modules
# * In the virtualenv: Update pip setuputils and wheel to support building new packages
FROM debian:11-slim AS build
RUN apt-get update && \
    apt-get install --no-install-suggests --no-install-recommends --yes python3-venv gcc libpython3-dev && \
    python3 -m venv /venv && \
    /venv/bin/pip install --upgrade pip setuptools wheel

# Build the virtualenv as a separate step: Only re-execute this step when requirements.txt changes
FROM build AS build-venv
COPY requirements.txt /requirements.txt
RUN /venv/bin/pip install --disable-pip-version-check -r /requirements.txt

# Copy the virtualenv into a distroless image
FROM gcr.io/distroless/python3-debian11
COPY --from=build-venv /venv /venv
COPY . /app
WORKDIR /app
ENTRYPOINT ["/venv/bin/python3", "psutil_example.py"]

Native dependencies

Finally if we have native dependencies, we can download them from a debian-based build stage, extract their contents to a temp directory (i.e. /dpkg), then copy those into the root distroless image during the final stage.

One way to generate a list of dependencies needed is to call apt-cache depends <your-lib-here>.
In our case we want to install the psycopg2 library, that has a native dependency on libpq. To find the package (and its dependencies) in debian, we'll first need the name of the package.

$ apt-get update
<snip>
Reading package lists... Done
$ apt-cache search libpq
<snip>
libpq5 - PostgreSQL C client library

Now that we have the name of the package (libpq5) we can see what dependencies it has.

$ apt-cache depends --recurse libpq5
libpq5
  Depends: libc6
  Depends: libgssapi-krb5-2
  Depends: libldap-2.4-2
  Depends: libssl1.1

We can see the pre-installed distroless dependencies listed in the python build file, the cc build file and the base build file. Looks like we'll need to add these dependencies.
NOTE: Dependencies might have dependencies, you can use the script here (written by @tuananh) to get all dependencies.

Final `Dockerfile`

# Build a virtualenv using the appropriate Debian release
# * Install python3-venv for the built-in Python3 venv module (not installed by default)
# * Install gcc libpython3-dev to compile C Python modules
# * In the virtualenv: Update pip setuputils and wheel to support building new packages
FROM debian:11-slim AS build
RUN apt-get update && \
    apt-get install --no-install-suggests --no-install-recommends --yes python3-venv gcc libpython3-dev && \
    python3 -m venv /venv && \
    /venv/bin/pip install --upgrade pip setuptools wheel
RUN cd /tmp && \
    apt-get update && \
    apt-get install -y --no-install-recommends \
        # install only deps
        curl \
        ca-certificates \
        openssl \
        && \
    apt-get download \
        # ca-certificates \
        \
        # additional python dependencies
        libpq5 \
        && \
    mkdir -p /dpkg/var/lib/dpkg/status.d/ && \
    for deb in *.deb; do \
        package_name=$(dpkg-deb -I ${deb} | awk '/^ Package: .*$/ {print $2}'); \ 
        echo "Process: ${package_name}"; \
        dpkg --ctrl-tarfile $deb | tar -Oxf - ./control > /dpkg/var/lib/dpkg/status.d/${package_name}; \
        dpkg --extract $deb /dpkg || exit 10; \
    done

# Build the virtualenv as a separate step: Only re-execute this step when requirements.txt changes
FROM build AS build-venv
COPY requirements.txt /requirements.txt
RUN /venv/bin/pip install --disable-pip-version-check -r /requirements.txt

# Copy the virtualenv into a distroless image
FROM gcr.io/distroless/python3-debian11
COPY --from=build-venv /venv /venv
COPY --from=build/dpkg /
COPY . /app
WORKDIR /app
ENTRYPOINT ["/venv/bin/python3", "psutil_example.py"]

Building multi-release jars (easily) with Gradle and Maven

Clayton Walker — Sun, 04 Dec 2022 05:41:51 +0000

Gradle

Use Cédric Champeau's mrjar plugin

plugins {
    id("me.champeau.mrjar") version "0.1.1"
}

multiRelease {
    targetVersions(8, 9)
}

See https://melix.github.io/mrjar-gradle-plugin/0.1/index.html for more details.

Maven

Use at least maven-compiler-plugin 3.7.1 which adds multiReleaseOutput

<configuration> 
    <release>9</release> 
    <compileSourceRoots> 
        <compileSourceRoot>${project.basedir}/src/main/java9</compileSourceRoot> 
    </compileSourceRoots> 
    <multiReleaseOutput>true</multiReleaseOutput>
</configuration>

Then set Multi-Release: true in the maven-jar-plugin

<configuration>
    <archive>
        <manifestEntries>
            <Multi-Release>true</Multi-Release>
        </manifestEntries>
    </archive>
</configuration>

How to add a `module-info.java`

todo

Stop using sourceCompatibility and targetCompatibility

Clayton Walker — Fri, 07 Jan 2022 00:20:22 +0000

And start using --release. As of JEP-247 released in java 9, the flag will allow you to compile for older releases of java without worrying about the dreaded NoSuchMethodError.

Stop talking and show me the code!

Gradle

tasks.withType(JavaCompile).configureEach {
    options.release = 9
}

Gradle (kts)

tasks.withType<JavaCompile>().configureEach {
    options.release.set(9)
}

Maven (xml) compiler plugin configuration

<configuration>
    <release>9</release>
</configuration>

or via properties

<properties>
    <maven.compiler.release>9</maven.compiler.release>
</properties>

Verify an application has picked up a java property

Clayton Walker — Thu, 16 Dec 2021 01:45:45 +0000

NOTE: This was written in response to the log4shell vulnerability CVE-2021-44228. -Dlog4j2.noFormatMsgLookup=true is not effective at mitigating the second of the two log4j vulnerabilities, CVE-2021-45046.

I've noticed these past few days people have been asking how to validate if a system property has been set.

Simple method (no code change)

The simplest method would be to add -Dlog4j2.noFormatMsgLookup=true to your JAVA_TOOL_OPTIONS environment variable, then verify that on startup you see the line

Picked up JAVA_TOOL_OPTIONS: -Dlog4j2.formatMsgNoLookups=true

printed to the console.

Code change method

The second way would be to check the system property itself, and print it out on startup. One example would be

System.out.println("log4j2.formatMsgNoLookups=" + System.getProperty("log4j2.formatMsgNoLookups"));

then validating

log4j2.formatMsgNoLookups=true

is printed to the console.

Forem: Clayton Walker

Snippet: How to handle non-issue (client) exceptions in spring boot

Bazel issues I'm following

Running c/c++ on the JVM

How to exclude classes from jacoco in Gradle

Managing Java installations on macOS

Fix dynamic agent loading warning in Gradle

Python and distroless: A simplified guide

No dependencies

Pure-python dependencies

Native dependencies

Final Dockerfile

Building multi-release jars (easily) with Gradle and Maven

Gradle

Maven

How to add a module-info.java

Stop using sourceCompatibility and targetCompatibility

Stop talking and show me the code!

Verify an application has picked up a java property

Simple method (no code change)

Code change method

Final `Dockerfile`

How to add a `module-info.java`