编译 java -use source 5 时出错

Question

如果这是一个愚蠢的问题，请原谅我，但我正在尝试编译我在 http://thisdataguy.com/2014/02/07/how-to-build-a-full-flume-interceptor-by-a-non-java-developer/ 找到的一些 java 代码

我对 java 编程非常陌生，当我运行代码时出现错误：

[INFO] Scanning for projects...
[INFO] ------------------------------------------------------------------------
[INFO] Building Unnamed - org.apache.flume:eventTweaker:jar:1.0
[INFO]    task-segment: [clean, package]
[INFO] ------------------------------------------------------------------------
[INFO] [clean:clean {execution: default-clean}]
[INFO] Deleting file set: /home/kwincott/jars/tweaker/target (included: [**], excluded:    [])
[INFO] [resources:resources {execution: default-resources}]
[WARNING] Using platform encoding (UTF-8 actually) to copy filtered resources, i.e. build is platform dependent!
[INFO] skip non existing resourceDirectory /home/kwincott/jars/tweaker/src/main/resources
[INFO] [compiler:compile {execution: default-compile}]
[INFO] Compiling 1 source file to /home/kwincott/jars/tweaker/target/classes
[INFO] ------------------------------------------------------------------------
[ERROR] BUILD FAILURE
[INFO] ------------------------------------------------------------------------
[INFO] Compilation failure

/home/kwincott/jars/tweaker/src/main/java/com/example/flume/interceptors   /eventTweaker.java:[18,3] annotations are not supported in -source 1.3
(use -source 5 or higher to enable annotations)
@Override

/home/kwincott/jars/tweaker/src/main/java/com/example/flume/interceptors/eventTweaker.java:[24,7] generics are not supported in -source 1.3
(use -source 5 or higher to enable generics)
Map<String, String> headers = event.getHeaders();

/home/kwincott/jars/tweaker/src/main/java/com/example/flume/interceptors/eventTweaker.java:[46,20] for-each loops are not supported in -source 1.3
(use -source 5 or higher to enable for-each loops)
for (Event event:events) {


[INFO] ------------------------------------------------------------------------
[INFO] For more information, run Maven with the -e switch
[INFO] ------------------------------------------------------------------------
[INFO] Total time: 2 seconds
[INFO] Finished at: Wed Aug 20 16:26:17 BST 2014
[INFO] Final Memory: 19M/303M
[INFO] ------------------------------------------------------------------------

Answer 1

显然，Maven 的编译器插件并不关心您实际使用的 Java 版本。错误信息提示您在pom.xml 中设置一些配置：

• Maven Compiler plugin documentation
• 也有帮助：What is the difference between using javac and javax.tools.JavaCompiler?

Answer 2

构建失败报告几乎说明了一切：

[18,3] annotations are not supported in -source 1.3
(use -source 5 or higher to enable annotations)
@Override

[24,7] generics are not supported in -source 1.3
(use -source 5 or higher to enable generics)
Map<String, String> headers = event.getHeaders();

[46,20] for-each loops are not supported in -source 1.3
(use -source 5 or higher to enable for-each loops)
for (Event event:events) {

（使用 -source 5 或更高版本来启用 for-each 循环）

您可能使用的是过时版本的 JDK（6 或更高版本）和/或 Maven（3.x 或更高版本）。更新到最新的 JDK 和 Maven 版本，错误应该消失了。

但是，正如构建报告末尾的 INFO 部分所述，for more information, run Maven with the -e switch。这将有助于您在将来调试问题。