java - maven-compiler-plugin如何与不同的jdk一起工作？

Question

$ mvn --version
Apache Maven 3.5.2 (138edd61fd100ec658bfa2d307c43b76940a5d7d; 2017-10-18T03:58:13-04:00)
Maven home: /usr/local/apache-maven
Java version: 1.8.0_151, vendor: Oracle Corporation
Java home: /usr/lib/jvm/java-8-oracle/jre
Default locale: en_CA, platform encoding: UTF-8
OS name: "linux", version: "4.4.0-98-generic", arch: "amd64", family: "unix"

机器上仅安装了jvm版本。

<小时/>

在pom.xml中，将source和target版本设置为1.4，

  <build>
    <plugins>
      <plugin>
        <groupId>org.apache.maven.plugins</groupId>
        <artifactId>maven-compiler-plugin</artifactId>
        <version>2.0.2</version>
        <configuration>
          <source>1.4</source>
          <target>1.4</target>
        </configuration>
      </plugin>
    </plugins>
  </build>

<小时/>

这是mvn package的输出，

$ mvn package
[INFO] Scanning for projects...
[INFO] 
[INFO] ------------------------------------------------------------------------
[INFO] Building mywebapp 1.0-SNAPSHOT
[INFO] ------------------------------------------------------------------------
Downloading from central: https://repo.maven.apache.org/maven2/org/apache/maven/plugins/maven-compiler-plugin/2.0.2/maven-compiler-plugin-2.0.2.pom
Downloaded from central: https://repo.maven.apache.org/maven2/org/apache/maven/plugins/maven-compiler-plugin/2.0.2/maven-compiler-plugin-2.0.2.pom (2.4 kB at 934 B/s)
....
[INFO] 
[INFO] --- maven-resources-plugin:2.6:resources (default-resources) @ mywebapp ---
[WARNING] Using platform encoding (UTF-8 actually) to copy filtered resources, i.e. build is platform dependent!
[INFO] skip non existing resourceDirectory /home/mohet01/git/Projects/myapp/mywebapp/src/main/resources
[INFO] 
[INFO] --- maven-compiler-plugin:2.0.2:compile (default-compile) @ mywebapp ---
...
Downloading from central: https://repo.maven.apache.org/maven2/org/codehaus/plexus/plexus-compiler-api/1.5.3/plexus-compiler-api-1.5.3.pom
Downloaded from central: https://repo.maven.apache.org/maven2/org/codehaus/plexus/plexus-compiler-api/1.5.3/plexus-compiler-api-1.5.3.pom (624 B at 700 B/s)
Downloading from central: https://repo.maven.apache.org/maven2/org/codehaus/plexus/plexus-compiler/1.5.3/plexus-compiler-1.5.3.pom
Downloaded from central: https://repo.maven.apache.org/maven2/org/codehaus/plexus/plexus-compiler/1.5.3/plexus-compiler-1.5.3.pom (1.5 kB at 1.8 kB/s)
...
Downloading from central: https://repo.maven.apache.org/maven2/org/codehaus/plexus/plexus-compiler-manager/1.5.3/plexus-compiler-manager-1.5.3.pom
Downloaded from central: https://repo.maven.apache.org/maven2/org/codehaus/plexus/plexus-compiler-manager/1.5.3/plexus-compiler-manager-1.5.3.pom (634 B at 732 B/s)
Downloading from central: https://repo.maven.apache.org/maven2/org/codehaus/plexus/plexus-compiler-javac/1.5.3/plexus-compiler-javac-1.5.3.pom
Downloaded from central: https://repo.maven.apache.org/maven2/org/codehaus/plexus/plexus-compiler-javac/1.5.3/plexus-compiler-javac-1.5.3.pom (797 B at 871 B/s)
Downloading from central: https://repo.maven.apache.org/maven2/org/codehaus/plexus/plexus-compilers/1.5.3/plexus-compilers-1.5.3.pom
Downloaded from central: https://repo.maven.apache.org/maven2/org/codehaus/plexus/plexus-compilers/1.5.3/plexus-compilers-1.5.3.pom (7.6 kB at 9.4 kB/s)
...
Downloading from central: https://repo.maven.apache.org/maven2/org/codehaus/plexus/plexus-compiler-api/1.5.3/plexus-compiler-api-1.5.3.jar
...
Downloading from central: https://repo.maven.apache.org/maven2/org/codehaus/plexus/plexus-compiler-manager/1.5.3/plexus-compiler-manager-1.5.3.jar
Downloaded from central: https://repo.maven.apache.org/maven2/org/codehaus/plexus/plexus-compiler-api/1.5.3/plexus-compiler-api-1.5.3.jar (20 kB at 20 kB/s)
...
Downloading from central: https://repo.maven.apache.org/maven2/org/codehaus/plexus/plexus-compiler-javac/1.5.3/plexus-compiler-javac-1.5.3.jar
...
Downloaded from central: https://repo.maven.apache.org/maven2/org/codehaus/plexus/plexus-compiler-javac/1.5.3/plexus-compiler-javac-1.5.3.jar (14 kB at 8.2 kB/s)
...

Downloaded from central: https://repo.maven.apache.org/maven2/org/codehaus/plexus/plexus-compiler-manager/1.5.3/plexus-compiler-manager-1.5.3.jar (5.3 kB at 2.1 kB/s)
.....

[INFO] Packaging webapp
[INFO] Assembling webapp [mywebapp] in [/home/mohet01/git/Projects/myapp/mywebapp/target/mywebapp-1.0-SNAPSHOT]
[INFO] Processing war project
[INFO] Copying webapp resources [/home/mohet01/git/Projects/myapp/mywebapp/src/main/webapp]
[INFO] Webapp assembled in [79 msecs]
[INFO] Building war: /home/mohet01/git/Projects/myapp/mywebapp/target/mywebapp-1.0-SNAPSHOT.war
[INFO] WEB-INF/web.xml already added, skipping
[INFO] ------------------------------------------------------------------------
[INFO] BUILD SUCCESS
[INFO] ------------------------------------------------------------------------
[INFO] Total time: 36.643 s
[INFO] Finished at: 2017-12-07T01:56:43-05:00
[INFO] Final Memory: 14M/140M
[INFO] ------------------------------------------------------------------------
$

<小时/>

在编译 java 源代码之前，maven 是否会从在线 maven 存储库中提取 1.4 版本的 javac 编译器？如何指向对应的jdk？

Answer 1

不，javac 能够编译为向后兼容的代码(有轻微异常(exception))