java 除了修改hadoop-env.sh之外，如何在hadoop中指定系统属性？
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How to specify system property in hadoop except modify hadoop-env.sh?
提问by zjffdu
I'd like to set system property (not hadoop property) when running hadoop jobs. I found that it's not easy to setting system property. Even I set the property in shell
我想在运行 hadoop 作业时设置系统属性（不是 hadoop 属性）。我发现设置系统属性并不容易。即使我在 shell 中设置了属性
export HADOOP_OPTS="$HADOOP_OPTS:-Dproperty=value"
It's still not working. The "-D" option of hadoop command line is only for Configuration, not system property. So the "-D" option also not working
它仍然无法正常工作。hadoop 命令行的“-D”选项仅用于配置，而不用于系统属性。所以“-D”选项也不起作用
Anyone has ideas ? thanks
任何人都有想法？谢谢
回答by Quetzalcoatl
Why not simply use -Dfoo.bar=examplein-line when starting the job via command line, like so:
为什么不在-Dfoo.bar=example通过命令行启动作业时简单地使用内联，如下所示：
hadoop jar example.jar com.example.ExampleTool -Dfoo.bar=example argument
hadoop jar example.jar com.example.ExampleTool -Dfoo.bar=example argument
In order to get at the property in code, use conf.get("foo.bar");
为了在代码中获取属性，请使用 conf.get("foo.bar");
Now if you genuinely need it to be set as a system property, you can set it at the start of your code using the value you got from Hadoop config like so:
现在，如果您真的需要将其设置为系统属性，则可以使用从 Hadoop 配置中获得的值在代码的开头进行设置，如下所示：
String property = conf.get("foo.bar");
System.setProperty("foo.bar", property);
回答by Jiacai Liu
The hadoopscript invoke java class like this
该hadoop脚本调用Java类这样
exec "$JAVA" $JAVA_HEAP_MAX $HADOOP_OPTS $CLASS "$@"
so, we can pass system-wide property like this:
所以，我们可以像这样传递系统范围的属性：
export HADOOP_OPTS="$HADOOP_OPTS -Dfoo=bar"
