在Maven Eclipse项目中更改Java SDK版本

Question

I have created new maven java project in eclipse by clicking File->New->Other->Maven->New Project . I found that projects is using java 1.5. In my PC exist only java 1.4 and java 8. I need to compile project using java 1.4 JDK. I go to Project->Properties-> JRE System Library and change to java 1.4. When I run main class I have error:

java.lang.UnsupportedClassVersionError: arr/ff (Unsupported major.minor version 49.0)
    at java.lang.ClassLoader.defineClass0(Native Method)
    at java.lang.ClassLoader.defineClass(ClassLoader.java:537)
    at java.security.SecureClassLoader.defineClass(SecureClassLoader.java:123)
    at java.net.URLClassLoader.defineClass(URLClassLoader.java:251)
    at java.net.URLClassLoader.access$100(URLClassLoader.java:55)
    at java.net.URLClassLoader$1.run(URLClassLoader.java:194)
    at java.security.AccessController.doPrivileged(Native Method)
    at java.net.URLClassLoader.findClass(URLClassLoader.java:187)
    at java.lang.ClassLoader.loadClass(ClassLoader.java:289)
    at sun.misc.Launcher$AppClassLoader.loadClass(Launcher.java:274)
    at java.lang.ClassLoader.loadClass(ClassLoader.java:235)
    at java.lang.ClassLoader.loadClassInternal(ClassLoader.java:302)

How to make project java 1.4 compatible?

Answer 1

First, I'd define a property to control the value. Something like,

<properties>
    <java.version>1.4</java.version>
</properties>

And then add a build stanza, like

<build>
    <plugins>
        <plugin>
            <groupId>org.apache.maven.plugins</groupId>
            <artifactId>maven-compiler-plugin</artifactId>
            <configuration>
                <verbose>true</verbose>
                <fork>true</fork>
                <debug>false</debug>
                <source>${java.version}</source>
                <target>${java.version}</target>
            </configuration>
        </plugin>
    </plugins>
</build>

Answer 2

Specify source and target Java version by this way:

<project>
  [...]
  <build>
    [...]
    <plugins>
      <plugin>
        <groupId>org.apache.maven.plugins</groupId>
        <artifactId>maven-compiler-plugin</artifactId>
        <version>3.3</version>
        <configuration>
          <source>1.5</source>
          <target>1.4</target>
        </configuration>
      </plugin>
    </plugins>
    [...]
  </build>
  [...]
</project>

• Read offical document .
• Read about Java version compatibility .

Answer 3

Usually IDEs use maven pom.xml file as a source of project configuration. Changing the compiler settings in the IDE not always has effect on the maven build. The best way to keep a project always manageable with maven is edit the pom.xml files and instruct the IDE to sync with maven.

Configure the maven compiler plugin in the pom.xml

<build>

<plugins>
    <plugin>
        <artifactId>maven-compiler-plugin</artifactId>
        <configuration>
            <source>1.5</source>
            <target>1.4</target>
        </configuration>
    </plugin>
</plugins>
...

• OR Set these properties (always in the pom)

<properties>
<maven.compiler.source>1.5</maven.compiler.source>
<maven.compiler.target>1.4</maven.compiler.target>
</properties>