为什么 Launch4j 找不到已安装的 JDK？

Question

I have Launch4j and JDK installed on my computer and I am trying to convert jar-file to exe. When I start Launch4j I get the following error:

This application requires a Java Runtime Environment 1.6.0

How can I fix this? What is the Launch4j search strategy to find installed jres/jdks?

JDK version:

java -version

Output:

java version "14" 2020-03-17 Java(TM) SE Runtime Environment (build 14+36-1461) Java HotSpot(TM) 64-Bit Server VM (build 14+36-1461, mixed mode, sharing)

I have JDK-path in both variables PATH and JAVA_HOME. I tried to uninstall the JDK and install JRE, but I first need to compile *.java to *.class files with the javac command. So in this case I have different versions of JDK and JRE.

The official documentation says:

Launch4j requires an xml configuration file for each output executable.

So I can use jre tag with jdkPreference attribute to specify a preference for a public JRE or a private JDK runtime in configuration file. But how can I add this to build.xml file?

build.xml:

<project name="launch4j" default="compile" basedir=".">
    <property name="src" location="src" />
    <property name="lib" location="lib" />
    <property name="build" location="build" />
    <property name="jar" location="./${ant.project.name}.jar" />
    <property name="launch4j.dir" location="." />
    <property name="maven" location="maven" />

    <path id="dist.classpath">
        <pathelement path="${build}" />
        <fileset dir="${lib}">
            <include name="**/*.jar" />
        </fileset>
    </path>

    <target name="init">
        <tstamp />
        <mkdir dir="${build}" />
    </target>

    <target name="compile" depends="init" description="compile the source">
        <javac srcdir="${src}" destdir="${build}" classpathref="dist.classpath" source="1.6" debug="on" includeantruntime="false" />
        <copy todir="${build}/images">
            <fileset dir="${src}/images">
                <include name="**/*" />
            </fileset>
        </copy>
        <copy todir="${build}">
            <fileset dir="${src}">
                <include name="**/*.properties" />
            </fileset>
        </copy>
    </target>

    <target name="jar" depends="compile" description="create jar">
        <fileset dir="${lib}" id="lib.dist.fileset">
            <include name="**/*.jar" />
        </fileset>
        <pathconvert pathsep=" " property="dist.classpath" refid="lib.dist.fileset">
            <map from="${lib}" to="./lib" />
        </pathconvert>
        <!-- Put everything in ${build} into a jar file -->
        <jar jarfile="${jar}">
            <fileset dir="${build}" excludes="**/messages_es.properties" />
            <manifest>
                <attribute name="Main-Class" value="net.sf.launch4j.Main" />
                <attribute name="Class-Path" value=". ${dist.classpath}" />
            </manifest>
        </jar>
    </target>

    <target name="demo" depends="jar" description="build the demos">
        <ant dir="./demo/ConsoleApp" inheritAll="false" />
        <ant dir="./demo/SimpleApp" inheritAll="false" />
    </target>

    <target name="clean" description="clean up">
        <delete dir="${build}" />
        <delete file="${jar}" />
        <ant dir="./demo/ConsoleApp" target="clean" inheritAll="false" />
        <ant dir="./demo/SimpleApp" target="clean" inheritAll="false" />
    </target>

    <target name="switch-to-maven" description="switch project to maven">
        <copy todir="." overwrite="true">
            <fileset dir="${maven}">
                <include name="**/*" />
            </fileset>
        </copy>
        <delete dir="${lib}" />
        <mkdir dir="./target" />
    </target>
</project>

Thanks

Answer 1

Launch4j seems to be limited with new java versions... In last update they shows up a detailed info about supported jvm, the last one is 1.8.9 and there is a ticket about compliance with java 9 and later... changelog and tickets launch4j

Answer 2

Instead of starting the launch4j.exe as windows executable, you may start the launch4.jar with your jdk. Therefore, mark the launch4j.jar in the file explorer, right click, choose open with, and reference your installed jdk, eg Open JDK platform binary

Answer 3

Install Oracle's JRE to get Launch4j to work.

Launch4j has limited recognition for versions and providers of the JVM. I had only AdoptOpenJDK 1.8 installed, and Launch4j's exe didn't work. When I installed Oracle's JRE 1.8, then it launched my jar application without any problems.

Even though I was getting the Java 1.6 Error message, I was still sure the jar application worked with Java 1.8. I think it was due to Launch4j being stale and not under recent updates at the time I integrated it into my application.