Apache Maven：-source 1.5中不支持Diamond运算符

Question

I build and run my Java Apache Camel code with the command

mvn clean compile camel:run

This command has always worked for me, however when I have code that uses diamond operator I get an error.

My diamond operator:

private List<RestPropertyDefinition> restProperties = new ArrayList<>();

My error:

[ERROR] Failed to execute goal org.apache.maven.plugins:maven-compiler-plugin:3.1:compile (default-compile) on project camel-rest-example: Compilation failure
[ERROR] /home/sindre/IdeaProjects/training/camelrestexample/src/main/java/com/test/EmployeeRoute.java:[21,73] diamond operator is not supported in -source 1.5
[ERROR]   (use -source 7 or higher to enable diamond operator)

My POM File:

<?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>com.test</groupId>
    <artifactId>camel-rest-example</artifactId>
    <version>1.0-SNAPSHOT</version>

    <dependencies>
        <!-- https://mvnrepository.com/artifact/org.apache.camel/camel-core -->
        <dependency>
            <groupId>org.apache.camel</groupId>
            <artifactId>camel-core</artifactId>
            <version>2.20.0</version>
        </dependency>

        <!-- https://mvnrepository.com/artifact/org.apache.camel/camel-spring -->
        <dependency>
            <groupId>org.apache.camel</groupId>
            <artifactId>camel-spring</artifactId>
            <version>2.20.0</version>
        </dependency>

        <dependency>
            <groupId>org.apache.camel</groupId>
            <artifactId>spi-annotations</artifactId>
            <version>2.20.0</version>
        </dependency>

        <!-- https://mvnrepository.com/artifact/org.apache.camel/camel-jms -->
        <dependency>
            <groupId>org.apache.camel</groupId>
            <artifactId>camel-jms</artifactId>
            <version>2.20.0</version>
        </dependency>

        <dependency>
            <groupId>org.apache.camel</groupId>
            <artifactId>camel-http4</artifactId>
            <version>2.20.0</version>
        </dependency>

        <dependency>
            <groupId>org.apache.camel</groupId>
            <artifactId>camel-quartz</artifactId>
            <version>2.20.0</version>
        </dependency>


        <!-- https://mvnrepository.com/artifact/org.apache.activemq/activemq-all -->
        <dependency>
            <groupId>org.apache.activemq</groupId>
            <artifactId>activemq-all</artifactId>
            <version>5.15.1</version>
        </dependency>

        <!-- https://mvnrepository.com/artifact/org.slf4j/slf4j-log4j12 -->
        <dependency>
            <groupId>org.slf4j</groupId>
            <artifactId>slf4j-log4j12</artifactId>
            <version>1.7.25</version>
            <scope>test</scope>
        </dependency>


    </dependencies>


    <build>
        <plugins>
            <!-- Allows the routes to be run via 'mvn camel:run' -->
            <plugin>
                <groupId>org.apache.camel</groupId>
                <artifactId>camel-maven-plugin</artifactId>
                <version>2.20.0</version>
            </plugin>
        </plugins>
    </build>
</project>

I am using Java 8, on Ubunut 18.04 with IntelliJ IDEA. It looks like IntelliJ believes that I am using Java 5? But I only have Java 8 installed on my machine

Answer 1

The compiler seems to assume source code level 1.5 by default.

Tell the compiler the explicit versions like this using the pom:

<build>
  <plugins>
    <plugin>
      <groupId>org.apache.maven.plugins</groupId>
      <artifactId>maven-compiler-plugin</artifactId>
      <version>2.5.1</version>
      <configuration>
        <source>1.8</source>
        <target>1.8</target>
      </configuration>
    </plugin>

Answer 2

This issue is because by default the Java Compiler is configured to use Java 1.5 for maximum compatibility, you can explicitly override for maven's compiler plugin by changing your configuration for the compiler plugin in your project pom.xml's plugins tag by adding the following entry

<plugin>
            <groupId>org.apache.maven.plugins</groupId>
            <artifactId>maven-compiler-plugin</artifactId>
            <version>3.1</version>
            <configuration>
                <source>1.8</source>
                <target>1.8</target>
            </configuration>
</plugin>

You can find further documentation on the usage of the Maven Compiler Plugin here