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What is "<release>" element on "<configuration>" for the "maven-compiler-plugin" in a JavaFX app

I used the org.openjfx:javafx-archetype-simple Maven archetype to start my first JavaFX project.
The resulting POM:
<project xmlns = "http://maven.apache.org/POM/4.0.0"
xmlns:xsi = "http://www.w3.org/2001/XMLSchema-instance"
xsi:schemaLocation = "http://maven.apache.org/POM/4.0.0 http://maven.apache.org/maven-v4_0_0.xsd">
<modelVersion>4.0.0</modelVersion>
<groupId>com.example.invoicing</groupId>
<artifactId>Invoicer</artifactId>
<version>1.0-SNAPSHOT</version>
<properties>
<project.build.sourceEncoding>UTF-8</project.build.sourceEncoding>
<maven.compiler.source>14</maven.compiler.source>
<maven.compiler.target>14</maven.compiler.target>
</properties>
<dependencies>
<dependency>
<groupId>org.openjfx</groupId>
<artifactId>javafx-controls</artifactId>
<version>14</version>
</dependency>
</dependencies>
<build>
<plugins>
<plugin>
<groupId>org.apache.maven.plugins</groupId>
<artifactId>maven-compiler-plugin</artifactId>
<version>3.8.1</version>
<configuration>
<release>14</release> 🡄 ???
</configuration>
</plugin>
<plugin>
<groupId>org.openjfx</groupId>
<artifactId>javafx-maven-plugin</artifactId>
<version>0.0.4</version>
<configuration>
<mainClass>com.example.invoicing.App</mainClass>
</configuration>
</plugin>
</plugins>
</build>
</project>
➥ What is the purpose of the <release>14</release> line in <configuration> for the plugin <artifactId>maven-compiler-plugin</artifactId>?
I found this documentation for the Maven Compiler Plugin, Compiling Your Java Sources. But it only mentions <!-- put your configurations here -->. So I do not know anything about specific configuration options here.
Is <release>14</release> the version of Java being used to compile? Is it the version of OpenJFX? Something else?
I tried using 28 arbitrarily. Doing a Maven > install threw this error with an unhelpful error message with no clue as to a release of what product:
Failed to execute goal org.apache.maven.plugins:maven-compiler-plugin:3.8.1:compile (default-compile) on project Invoicer: Fatal error compiling

The release flag is equivalent to specifying the source and target of the same value for the compiler plugin. It supports the -release argument for the Java compiler since Java-9.
<plugin>
<groupId>org.apache.maven.plugins</groupId>
<artifactId>maven-compiler-plugin</artifactId>
<version>3.8.1</version>
<configuration>
<source>14</source>
<target>14</target>
</configuration>
</plugin>
Note: For the same reason, you can get rid of the redundant properties declared as
<maven.compiler.source>14</maven.compiler.source>
<maven.compiler.target>14</maven.compiler.target>
Further: What is the --release flag in the Java 9 compiler? | The -release flag in javac was introduced to Compile for Older Platform Versions.
To complete the answer over the part where you've tried the version value as 28. While using Maven version -
Apache Maven 3.6.1 (d66c9c0b3152b2e69ee9bac180bb8fcc8e6af555; 2019-04-05T00:30:29+05:30)
The error message reads very clearly what it should (if you could share the complete logs in the question)
[ERROR] Failed to execute goal org.apache.maven.plugins:maven-compiler-plugin:3.8.1:compile (default-compile) on project forty-bits-of-java:
Fatal error compiling: error: release version 28 not supported

The compile options page states that this ends up as the -release argument passed to javac.
And about --release release:
Compiles against the public, supported and documented API for a specific VM version. Supported release targets are 6, 7, 8, and 9.
As I understand it, Java 9 introduced a feature that helps developers build on a recent compiler, targeting an older runtime, but at the same time preventing the old problem that let code compile with references to newer APIs while being targeted at old runtimes.
See: JEP 247: Compile for Older Platform Versions
Ex: If you use Java 8 to compile code that uses new Java 8 APIs (such as Collection.stream()), with a target of 1.7, this code compiles but will fail at runtime on Java 7 with a NoSuchMethodError.
On JDK 9, if you use --release 1.7, the compiler will know that Collection.stream() can't be correctly targeted at Java 7 and will fail the build.

tl;dr
In your POM, replace the two tags source & target as seen here:
<properties>
<project.build.sourceEncoding>UTF-8</project.build.sourceEncoding>
<!--The following `source` and `target` tags are now replaced by `release` seen further down below.-->
<!--<maven.compiler.source>14</maven.compiler.source>-->
<!--<maven.compiler.target>14</maven.compiler.target>-->
</properties>
…with the new release tag, placed further down in POM:
<build>
<pluginManagement><!-- lock down plugins versions to avoid using Maven defaults (may be moved to parent pom) -->
<plugins>
…
<plugin>
<artifactId>maven-compiler-plugin</artifactId>
<version>3.8.1</version>
<configuration>
<!--Enable Java language preview features. Specify Java version.-->
<!--This `release` tag replaced the pair of `source` and `target` tags seen commented-out near top of this POM.-->
<release>14</release>
</configuration>
</plugin>
…
…to tell the Java compiler the version of Java on which you intend to deploy. This tag passes a release flag to the Java compiler. The compiler errors out any of your code trying to use an API added to later versions of Java.
See another Question: What is the --release flag in the Java 9 compiler?
Details
Both Answers by Naman and by ernest_k are correct and important. But I need to write this Answer to combine them and show the direct solution.
Problem
The issue is that JEP 247: Compile for Older Platform Versions added a feature in Java 9 for a new compiler flag -release to replace the combination of older -source, -target, and -bootclasspath flags. This plugs a hole that plagued programmers trying to work on the latest compiler while writing code limited to making API calls of an earlier version of Java.
For example, I may be writing on my Mac using Java 12 yet deploying to a server running Java 8. I want the compiler to stop me from accidentally using features that arrived in later versions of Java. Otherwise, my app will succeed at compile-time yet fail at run-time when those features are unavailable on the older JVM.
To quote the JEP:
Summary
Enhance javac so that it can compile Java programs to run on selected older versions of the platform.
Motivation
javac provides two command line options, -source and -target, which can be used to select the version of the Java language accepted by the compiler and the version of the class files it produces, respectively. By default, however, javac compiles against the most-recent version of the platform APIs. The compiled program can therefore accidentally use APIs only available in the current version of the platform. Such programs cannot run on older versions of the platform, regardless of the values passed to the -source and -target options. This is a long-term usability pain point, since users expect that by using these options they'll get class files that can run on the the platform version specified by -target.
Solution
In a Maven-driven project, we pass those flags to the Java compiler by setting tags on our Maven POM file.
In your Maven POM file’s tag hierarchy of:
<project> …
<build> …
<pluginManagement> …
<plugins> …
<plugin>
<artifactId>maven-compiler-plugin</artifactId>
…nest the following tag hierarchy, within which we specify our desired deployment version of Java.
<configuration>
<release>14</release>
By the way, if using a version of Java offering "preview" features, we can nest a further tag and value if we wish to enable those preview features.
<compilerArgs>--enable-preview</compilerArgs>
The old-school settings replaced by the new release tag were a pair of tags, source and target. These two could be set in Maven to be passed along to the Java compiler. So if you add the release tag seen above, check to see if your POM has this pair of tags. If found, delete them.
<properties>
<project.build.sourceEncoding>UTF-8</project.build.sourceEncoding>
<maven.compiler.source>14</maven.compiler.source> 🡄 Delete if using `release` tag.
<maven.compiler.target>14</maven.compiler.target> 🡄 Delete if using `release` tag.
</properties>
Example POM file
Here is a complete example POM file for Maven 3.6.3, for a basic Java project.
We are using all the latest versions of various plugins and dependencies. This example uses Java 15 with preview features such as Records enabled.
<?xml version="1.0" encoding="UTF-8"?>
<project xmlns = "http://maven.apache.org/POM/4.0.0"
xmlns:xsi = "http://www.w3.org/2001/XMLSchema-instance"
xsi:schemaLocation = "http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd">
<modelVersion>4.0.0</modelVersion>
<groupId>work.basil.demo</groupId>
<artifactId>Demo5</artifactId>
<version>1.0-SNAPSHOT</version>
<name>Demo5</name>
<url>http://www.example.com</url>
<properties>
<project.build.sourceEncoding>UTF-8</project.build.sourceEncoding>
<!--The following `source` and `target` tags are now replaced by `release` seen further down below.-->
<!--<maven.compiler.source>15</maven.compiler.source>-->
<!--<maven.compiler.target>15</maven.compiler.target>-->
</properties>
<dependencies>
<dependency>
<groupId>org.junit.jupiter</groupId>
<artifactId>junit-jupiter</artifactId>
<version>5.7.0-M1</version>
<scope>test</scope>
</dependency>
</dependencies>
<build>
<pluginManagement><!-- lock down plugins versions to avoid using Maven defaults (may be moved to parent pom) -->
<plugins>
<!-- clean lifecycle, see https://maven.apache.org/ref/current/maven-core/lifecycles.html#clean_Lifecycle -->
<plugin>
<artifactId>maven-clean-plugin</artifactId>
<version>3.1.0</version>
</plugin>
<!-- default lifecycle, jar packaging: see https://maven.apache.org/ref/current/maven-core/default-bindings.html#Plugin_bindings_for_jar_packaging -->
<plugin>
<artifactId>maven-resources-plugin</artifactId>
<version>3.1.0</version>
</plugin>
<plugin>
<artifactId>maven-compiler-plugin</artifactId>
<version>3.8.1</version>
<configuration>
<!--Enable Java language preview features. Specify Java version.-->
<!--This `release` tag replaced the pair of `source` and `target` tags seen commented-out near top of this POM.-->
<release>15</release>
<compilerArgs>
--enable-preview
</compilerArgs>
</configuration>
</plugin>
<plugin>
<artifactId>maven-surefire-plugin</artifactId>
<version>3.0.0-M4</version>
</plugin>
<plugin>
<artifactId>maven-jar-plugin</artifactId>
<version>3.2.0</version>
</plugin>
<plugin>
<artifactId>maven-install-plugin</artifactId>
<version>3.0.0-M1</version>
</plugin>
<plugin>
<artifactId>maven-deploy-plugin</artifactId>
<version>3.0.0-M1</version>
</plugin>
<!-- site lifecycle, see https://maven.apache.org/ref/current/maven-core/lifecycles.html#site_Lifecycle -->
<plugin>
<artifactId>maven-site-plugin</artifactId>
<version>3.8.2</version>
</plugin>
<plugin>
<artifactId>maven-project-info-reports-plugin</artifactId>
<version>3.1.0</version>
</plugin>
</plugins>
</pluginManagement>
</build>
</project>
JavaFX
You mentioned JavaFX in your Question. Note that this discussion applies to any and all Maven-driven Java projects. This includes JavaFX projects as well as Jakarta Servlets, console apps, and so on. Nothing here is specific to JavaFX.

Team City Build Failed : diamond operator is not supported in -source 1.6 [duplicate]

I wrote some Maven code in Netbeans that has approximately more than 2000 lines. When I compile it on Netbeans, everything is fine, but if I want to run it on command line, I will get these errors:
generics are not supported in -source 1.3
(use -source 5 or higher to enable generics)
ArrayList<ArrayList<Integer>> list = new ArrayList<ArrayList<Integer>>();
generics are not supported in -source 1.3
(use -source 5 or higher to enable generics)
HashSet<Double> resid_List = new HashSet<Double>(Arrays.asList(resid_val));
generics are not supported in -source 1.3
(use -source 5 or higher to enable generics)
List<Integer> ind_ovlpList = new ArrayList<Integer>(Arrays.asList(ind_ovlp));
generics are not supported in -source 1.3
(use -source 5 or higher to enable generics)
public class ColumnComparator implements Comparator<double[]> {
annotations are not supported in -source 1.3
(use -source 5 or higher to enable annotations)
#Override
I tried to use Java 1.3.1, compiler errors, but I got more errors. I found from other posts that I should modify pom.xml, but I do not know how. Here is my pom.xml
<project xmlns="http://maven.apache.org/POM/4.0.0" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd">
<modelVersion>4.0.0</modelVersion>
<groupId>com.mycompany</groupId>
<artifactId>mavenmain</artifactId>
<version>1.0-SNAPSHOT</version>
<packaging>jar</packaging>
<name>mavenmain</name>
<url>http://maven.apache.org</url>
<properties>
<project.build.sourceEncoding>UTF-8</project.build.sourceEncoding>
</properties>
<dependencies>
<dependency>
<groupId>junit</groupId>
<artifactId>junit</artifactId>
<version>3.8.1</version>
<scope>test</scope>
</dependency>
<dependency>
<groupId>gov.nist.math</groupId>
<artifactId>jama</artifactId>
<version>1.0.2</version>
</dependency>
</dependencies>
</project>
It would be great if you can help me!

maven-compiler-plugin it's already present in plugins hierarchy dependency in pom.xml. Check in Effective POM.
For short you can use properties like this:
<properties>
<maven.compiler.source>1.8</maven.compiler.source>
<maven.compiler.target>1.8</maven.compiler.target>
</properties>
I'm using Maven 3.2.5.

<project>
[...]
<build>
[...]
<plugins>
<plugin>
<groupId>org.apache.maven.plugins</groupId>
<artifactId>maven-compiler-plugin</artifactId>
<version>(whatever version is current)</version>
<configuration>
<!-- or whatever version you use -->
<source>1.7</source>
<target>1.7</target>
</configuration>
</plugin>
</plugins>
[...]
</build>
[...]
</project>
See the config page for the maven compiler plugin:
http://maven.apache.org/plugins/maven-compiler-plugin/examples/set-compiler-source-and-target.html
Oh, and: don't use Java 1.3.x, current versions are Java 11 or 17.

Generally you don't want to value only the source version (javac -source 1.8 for example) but you want to value both the source and the target version (javac -source 1.8 -target 1.8 for example).
Note that from Java 9, you have a way to convey both information and in a more robust way for cross-compilation compatibility (javac -release 9).
Maven that wraps the javac command provides multiple ways to convey all these JVM standard options.
How to specify the JDK version?
Using maven-compiler-plugin or maven.compiler.source/maven.compiler.target properties to specify the source and the target are equivalent.
<plugins>
<plugin>
<artifactId>maven-compiler-plugin</artifactId>
<configuration>
<source>1.8</source>
<target>1.8</target>
</configuration>
</plugin>
</plugins>
and
<properties>
<maven.compiler.source>1.8</maven.compiler.source>
<maven.compiler.target>1.8</maven.compiler.target>
</properties>
are equivalent according to the Maven documentation of the compiler plugin
since the <source> and the <target> elements in the compiler configuration use the properties maven.compiler.source and maven.compiler.target if they are defined.
source
The -source argument for the Java compiler.
Default value is: 1.6.
User property is: maven.compiler.source.
target
The -target argument for the Java compiler.
Default value is: 1.6.
User property is: maven.compiler.target.
About the default values for source and target, note that
since the 3.8.0 of the maven compiler, the default values have changed from 1.5 to 1.6.
<release> tag — new way to specify Java version in maven-compiler-plugin 3.6
You can use the release argument :
<plugin>
<groupId>org.apache.maven.plugins</groupId>
<artifactId>maven-compiler-plugin</artifactId>
<version>3.8.0</version>
<configuration>
<release>9</release>
</configuration>
</plugin>
You could also declare just the user property maven.compiler.release:
<properties>
<maven.compiler.release>9</maven.compiler.release>
</properties>
But at this time the last one will not be enough as the maven-compiler-plugin default version you use doesn't rely on a recent enough version.
The Maven release argument conveys release to the Java compiler to access the JVM standard option newly added to Java 9, JEP 247: Compile for Older Platform Versions.
Compiles against the public, supported and documented API for a
specific VM version.
This way provides a standard way to specify the same version for the source, the target and the bootstrap JVM options.
Note that specifying the bootstrap is a good practice for cross compilations and it will not hurt if you don't make cross compilations either.
Which is the best way to specify the JDK version?
Java 8 and below
Neither maven.compiler.source/maven.compiler.target properties or using the maven-compiler-plugin is better.
It changes nothing in the facts since finally the two ways rely on the same properties and the same mechanism : the maven core compiler plugin.
Well, if you don't need to specify other properties or behavior than Java versions in the compiler plugin, using this way makes more sense as this is more concise:
<properties>
<maven.compiler.source>1.8</maven.compiler.source>
<maven.compiler.target>1.8</maven.compiler.target>
</properties>
Java 9 and later
The release argument (third point) is a way to strongly consider if you want to use the same version for the source and the target.

I faced same issue in eclipse neon simple maven java project
But I add below details inside pom.xml file
<build>
<plugins>
<plugin>
<groupId>org.apache.maven.plugins</groupId>
<artifactId>maven-compiler-plugin</artifactId>
<version>3.6.1</version>
<configuration>
<source>1.8</source>
<target>1.8</target>
</configuration>
</plugin>
</plugins>
</build>
After right click on project > maven > update project (checked force update)
Its resolve me to display error on project
Hope it's will helpful
Thansk

<plugin>
<groupId>org.apache.maven.plugins</groupId>
<artifactId>maven-compiler-plugin</artifactId>
<version>3.3</version>
<configuration>
<fork>true</fork>
<source>1.8</source>
<target>1.8</target>
</configuration>
</plugin>

Compilation error when executing through pom.xml

I have a maven project and when I try to execute through pom.xml file, getting the compilation error as follows
C:testscripts/TC_Maintenance.java:[137,48] "strings in switch are not supported in -source 1.6
(use -source 7 or higher to enable strings in switch)"
I have configured jdk 1.8 in maven, could you please resolve this issue.
We have parent pom as well that is called in the pom.xml file
<plugin>
<groupId>org.apache.maven.plugins</groupId>
<artifactId>maven-compiler-plugin</artifactId>
<version>3.7.0</version>
<configuration>
<source>1.8</source>
<target>1.8</target>
</configuration>
</plugin>

Please validate compiler option in pom.xml file also validate your maven is using correct java version using mvn -version.
<project>
[...]
<properties>
<maven.compiler.source>1.8</maven.compiler.source>
<maven.compiler.target>1.8</maven.compiler.target>
</properties>
[...]
</project>
more details about in set-compiler-source-and-target

Please make sure that you have added this plugin to your pom.xml. This will ensure that the build task uses version 1.7. We often miss this.
<plugin>
<groupId>org.apache.maven.plugins</groupId>
<artifactId>maven-compiler-plugin</artifactId>
<configuration>
<source>1.8</source>
<target>1.8</target>
</configuration>
</plugin>

Instead of including it as a plug-in, I added the section under properties above Dependencies:
<properties>
<project.build.sourceEncoding>UTF-8</project.build.sourceEncoding>
<maven.compiler.source>1.8</maven.compiler.source>
<maven.compiler.target>1.8</maven.compiler.target>
</properties>
I should add that this is what I believe has already been offered, but I think you added the code in the wrong area of your pom.xml, at least based upon your commented reply (it's hard to read as a comment - no formatting)

By default Maven project takes jre file try to change it to JDK JRE and check whether you are able to resolve this issue.

Eclipse Maven and Java 8 problems

I moved from simple web app to maven web app and with Eclipse Neon I encountered a frustrating problem: after I add in pom.xml the specification to use Java 8 or 7, it doesn't work.
To verify if it works I write a simple class where I use a try(expression) declaration.
What should I have to do to use Java 8 in maven (I have installed and it works in normal web app)?
The code of pom.xml is this:
<project xmlns="http://maven.apache.org/POM/4.0.0" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd">
<modelVersion>4.0.0</modelVersion>
<groupId>com.webdata</groupId>
<artifactId>WebParser</artifactId>
<version>0.0.1-SNAPSHOT</version>
<packaging>jar</packaging>
<name>WebParser</name>
<url>http://maven.apache.org</url>
<properties>
<project.build.sourceEncoding>UTF-8</project.build.sourceEncoding>
</properties>
<build>
<plugins>
<plugin>
<groupId>org.apache.maven.plugins</groupId>
<artifactId>maven-compiler-plugin</artifactId>
<version>3.5.1</version>
<configuration>
<source>1.8</source>
<target>1.8</target>
</configuration>
</plugin>
</plugins>
</build>
<dependencies>
<dependency>
<groupId>junit</groupId>
<artifactId>junit</artifactId>
<version>3.8.1</version>
<scope>test</scope>
</dependency>
<dependency>
<groupId>net.sourceforge.htmlunit</groupId>
<artifactId>htmlunit</artifactId>
<version>2.23</version>
</dependency>
</dependencies>
</project>

First, your JAVA_HOME must point to a JDK 1.8.
Else if is not the case, you must specify a JDK 1.8 as source and target in the compiler configuration of your pom.xml in this way :
<plugin>
<groupId>org.apache.maven.plugins</groupId>
<artifactId>maven-compiler-plugin</artifactId>
<configuration>
<source>1.8</source>
<target>1.8</target>
<compilerVersion>1.8</compilerVersion>
<fork>true</fork>
<executable>D:\jdk1.8\bin\javac</executable>
</configuration>
</plugin>
Then, in eclipse, you must check in Preferences that :
Java->Installed JREs has a 1.8 JRE/JDK installed.
You could set the following as default if you want to use the 1.8 for any new created projects in your Eclipse :
Java->Installed JREs : select the 1.8.
Java->Compiler : select the JDK compiler compliance level to 1.8.
If the default preferences don't use 1.8 compilation compliance and JDK/JRE or that the project was created outside from this Eclipse with preferences set to 1.8 compilation compliance and JDK/JRE, you should check and maybe adjust properties of your Eclipse project
To do it, go in the properties of your project, then Java Build Path and in the Libraries tab. You must check that the JRE System Library uses Java 1.8. If it is not the case, remplace it with the 1.8 version.
When it is done, always in the properties of your project, go to Java Compiler and check that you use JDK compiler compliance with Java 1.8.
It should work.

It's funny :))
I searched 3-4 hours and I tried few methods and only after I asked here I found the solution :)
Right click on the project -> Properties -> Java Compiler -> uncheck 'Use compilance from execution...' and choose '1.8'

In pom.xml, defined this maven.compiler.source properties to tell Maven to use Java 8 to compile the project.
Maven Properties Java 8
<properties>
<maven.compiler.target>1.8</maven.compiler.target>
<maven.compiler.source>1.8</maven.compiler.source>
</properties>
Compiler Plugin - Alternative, configure the plugin directly.
<build>
<plugins>
<plugin>
<groupId>org.apache.maven.plugins</groupId>
<artifactId>maven-compiler-plugin</artifactId>
<version>3.6.1</version>
<configuration>
<source>1.8</source>
<target>1.8</target>
</configuration>
</plugin>
</plugins>
</build>

This worked for me:
<properties>
<maven.compiler.source>1.8</maven.compiler.source>
<maven.compiler.target>1.8</maven.compiler.target>
</properties>
as mentioned here -> maven-compiler-plugin
Don't forget to update Maven project -> Alt + F5.

How do you specify the Java compiler version in a pom.xml file?

I wrote some Maven code in Netbeans that has approximately more than 2000 lines. When I compile it on Netbeans, everything is fine, but if I want to run it on command line, I will get these errors:
generics are not supported in -source 1.3
(use -source 5 or higher to enable generics)
ArrayList<ArrayList<Integer>> list = new ArrayList<ArrayList<Integer>>();
generics are not supported in -source 1.3
(use -source 5 or higher to enable generics)
HashSet<Double> resid_List = new HashSet<Double>(Arrays.asList(resid_val));
generics are not supported in -source 1.3
(use -source 5 or higher to enable generics)
List<Integer> ind_ovlpList = new ArrayList<Integer>(Arrays.asList(ind_ovlp));
generics are not supported in -source 1.3
(use -source 5 or higher to enable generics)
public class ColumnComparator implements Comparator<double[]> {
annotations are not supported in -source 1.3
(use -source 5 or higher to enable annotations)
#Override
I tried to use Java 1.3.1, compiler errors, but I got more errors. I found from other posts that I should modify pom.xml, but I do not know how. Here is my pom.xml
<project xmlns="http://maven.apache.org/POM/4.0.0" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd">
<modelVersion>4.0.0</modelVersion>
<groupId>com.mycompany</groupId>
<artifactId>mavenmain</artifactId>
<version>1.0-SNAPSHOT</version>
<packaging>jar</packaging>
<name>mavenmain</name>
<url>http://maven.apache.org</url>
<properties>
<project.build.sourceEncoding>UTF-8</project.build.sourceEncoding>
</properties>
<dependencies>
<dependency>
<groupId>junit</groupId>
<artifactId>junit</artifactId>
<version>3.8.1</version>
<scope>test</scope>
</dependency>
<dependency>
<groupId>gov.nist.math</groupId>
<artifactId>jama</artifactId>
<version>1.0.2</version>
</dependency>
</dependencies>
</project>
It would be great if you can help me!

maven-compiler-plugin it's already present in plugins hierarchy dependency in pom.xml. Check in Effective POM.
For short you can use properties like this:
<properties>
<maven.compiler.source>1.8</maven.compiler.source>
<maven.compiler.target>1.8</maven.compiler.target>
</properties>
I'm using Maven 3.2.5.

<project>
[...]
<build>
[...]
<plugins>
<plugin>
<groupId>org.apache.maven.plugins</groupId>
<artifactId>maven-compiler-plugin</artifactId>
<version>(whatever version is current)</version>
<configuration>
<!-- or whatever version you use -->
<source>1.7</source>
<target>1.7</target>
</configuration>
</plugin>
</plugins>
[...]
</build>
[...]
</project>
See the config page for the maven compiler plugin:
http://maven.apache.org/plugins/maven-compiler-plugin/examples/set-compiler-source-and-target.html
Oh, and: don't use Java 1.3.x, current versions are Java 11 or 17.

Generally you don't want to value only the source version (javac -source 1.8 for example) but you want to value both the source and the target version (javac -source 1.8 -target 1.8 for example).
Note that from Java 9, you have a way to convey both information and in a more robust way for cross-compilation compatibility (javac -release 9).
Maven that wraps the javac command provides multiple ways to convey all these JVM standard options.
How to specify the JDK version?
Using maven-compiler-plugin or maven.compiler.source/maven.compiler.target properties to specify the source and the target are equivalent.
<plugins>
<plugin>
<artifactId>maven-compiler-plugin</artifactId>
<configuration>
<source>1.8</source>
<target>1.8</target>
</configuration>
</plugin>
</plugins>
and
<properties>
<maven.compiler.source>1.8</maven.compiler.source>
<maven.compiler.target>1.8</maven.compiler.target>
</properties>
are equivalent according to the Maven documentation of the compiler plugin
since the <source> and the <target> elements in the compiler configuration use the properties maven.compiler.source and maven.compiler.target if they are defined.
source
The -source argument for the Java compiler.
Default value is: 1.6.
User property is: maven.compiler.source.
target
The -target argument for the Java compiler.
Default value is: 1.6.
User property is: maven.compiler.target.
About the default values for source and target, note that
since the 3.8.0 of the maven compiler, the default values have changed from 1.5 to 1.6.
<release> tag — new way to specify Java version in maven-compiler-plugin 3.6
You can use the release argument :
<plugin>
<groupId>org.apache.maven.plugins</groupId>
<artifactId>maven-compiler-plugin</artifactId>
<version>3.8.0</version>
<configuration>
<release>9</release>
</configuration>
</plugin>
You could also declare just the user property maven.compiler.release:
<properties>
<maven.compiler.release>9</maven.compiler.release>
</properties>
But at this time the last one will not be enough as the maven-compiler-plugin default version you use doesn't rely on a recent enough version.
The Maven release argument conveys release to the Java compiler to access the JVM standard option newly added to Java 9, JEP 247: Compile for Older Platform Versions.
Compiles against the public, supported and documented API for a
specific VM version.
This way provides a standard way to specify the same version for the source, the target and the bootstrap JVM options.
Note that specifying the bootstrap is a good practice for cross compilations and it will not hurt if you don't make cross compilations either.
Which is the best way to specify the JDK version?
Java 8 and below
Neither maven.compiler.source/maven.compiler.target properties or using the maven-compiler-plugin is better.
It changes nothing in the facts since finally the two ways rely on the same properties and the same mechanism : the maven core compiler plugin.
Well, if you don't need to specify other properties or behavior than Java versions in the compiler plugin, using this way makes more sense as this is more concise:
<properties>
<maven.compiler.source>1.8</maven.compiler.source>
<maven.compiler.target>1.8</maven.compiler.target>
</properties>
Java 9 and later
The release argument (third point) is a way to strongly consider if you want to use the same version for the source and the target.

I faced same issue in eclipse neon simple maven java project
But I add below details inside pom.xml file
<build>
<plugins>
<plugin>
<groupId>org.apache.maven.plugins</groupId>
<artifactId>maven-compiler-plugin</artifactId>
<version>3.6.1</version>
<configuration>
<source>1.8</source>
<target>1.8</target>
</configuration>
</plugin>
</plugins>
</build>
After right click on project > maven > update project (checked force update)
Its resolve me to display error on project
Hope it's will helpful
Thansk

<plugin>
<groupId>org.apache.maven.plugins</groupId>
<artifactId>maven-compiler-plugin</artifactId>
<version>3.3</version>
<configuration>
<fork>true</fork>
<source>1.8</source>
<target>1.8</target>
</configuration>
</plugin>