[英]py4j: how to launch the java Gateway from Python
I am able to interact with my sample Java program in Python, by opening my Java program and then using the following Python code: 通过打开Java程序,然后使用以下Python代码,我可以在Python中与示例Java程序进行交互:
from py4j.java_gateway import JavaGateway
gg = JavaGateway()
sw = gg.entry_point.getInstance()
sw.run()
...
However this has the disadvantage that I have to somehow open the Java program before using this code. 但是,这样做的缺点是,在使用此代码之前,我必须以某种方式打开Java程序。
I found that there is a method called launch_gateway which seems very convenient soo to this aim. 我发现有一个名为launch_gateway的方法对于实现此目标似乎非常方便。
py4j.java_gateway.launch_gateway(jarpath="path_to_my_jar.jar")
However, I am unable to connect to my Java program if launched in this way. 但是,如果以这种方式启动,则无法连接到Java程序。
I tried to use the following code: 我尝试使用以下代码:
port = py4j.java_gateway.launch_gateway(jarpath="path_to_my_jar.jar")
gp = GatewayParameters(port=port)
gg = JavaGateway(gateway_parameters=gp)
sw = gg.entry_point.getInstance()
But I get the following error: 但是我收到以下错误:
An error occurred while calling t.getInstance. Trace:
py4j.Py4JException: Target Object ID does not exist for this gateway :t
I guess I am doing something wrong in the way I try to connect to the gateway. 我想我尝试连接到网关的方式出了问题。
Any suggestion? 有什么建议吗?
Thanks 谢谢
Barthelemy, you are right! 巴泰勒米,你是对的! I initially misinterpreted how this works.
我最初误解了它是如何工作的。
launch_gateway
runs the gateway in py4j.jar, which is useful to interact with a standard JVM, but obviously does not contain custom code. launch_gateway
在launch_gateway
运行网关,该网关对于与标准JVM交互很有用,但显然不包含自定义代码。
However, as you suggested, the classpath
parameter allows you to load additional custom Java code. 但是,按照您的建议,
classpath
参数允许您加载其他自定义Java代码。
This is a "minimal example": 这是一个“最小示例”:
from py4j.java_gateway import JavaGateway
gg = JavaGateway.launch_gateway(classpath="/path/my_jar.jar")
myclass_instance = gg.jvm.my_class_package_name.MyClass()
result = myclass_instance.my_method()
Note that my_jar.jar
does not have to start a gateway. 请注意,
my_jar.jar
不必启动网关。
launch_gateway
gives you nice features such as: die_on_exit
, stdout/stdin redirection, and automatic port selection. launch_gateway
为您提供了不错的功能,例如: die_on_exit
,stdout / stdin重定向和自动端口选择。
I see two potential problems: 我看到两个潜在的问题:
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