This article mainly introduces the example of JPype calling JAVA in python. The editor thinks it is quite good, so I will share it with you now and give it as a reference. Let’s follow the editor and take a look
1. Brief introduction to JPype
1. What is JPype?
JPype is a tool that allows python code to easily call Java code, thereby overcoming python's shortcomings in certain areas (such as server-side programming).
2. What is the difference between JPype and Jython (the successor of JPython)?
1) The running environment is different: jython runs on jvm, while the actual running environment of JPype is still python runtime, but an embedded jvm is started during operation;
2) The users are different: jython is for java programs, and JPype is for python programmers.
2. JPype installation
1. Install Python2.7 and JAVA1.6 first
2. Install JPype-0.5.4.2.win32-py2.7 .exe(/projects/jpype/files/JPype/0.5.4/)
3. Ubuntu12.04 installation command: sudo apt-get install python-jpype
3. JPype Instructions for use
1. Start JVM
The startJVM() function provided by JPype is used to start the JAVA virtual machine, so this must be called before any subsequent JAVA code is called. Method starts the JAVA virtual machine.
Definition of jpype.startJVM()
startJVM(jvm, *args) Parameters of jpype.startJVM()
Parameter 1: jvm, describe your system The path where the jvm.dll file is located, such as "C:Program FilesIBMJava50jreinj9vmjvm.dll". The default JVM path can be obtained by calling jpype.getDefaultJVMPath().
Parameter 2: args, which is an optional parameter, will be passed directly to the JVM by JPype as the startup parameter of the Java virtual machine. All legal JVM startup parameters apply here, for example:
-agentlib:libname[=options]
-classpath classpath
-verbose
-Xint 2. Shut down the JVM
After using the JVM, you can shut down the JVM through jpype.shutdownJVM(). This function has no input parameters. When the python program exits, the JVM will automatically shut down.
3. Reference third-party Java extension packages
Many times, third-party Java extension packages need to be called in python projects, which is also an important use of JPype.
By adding: -Djava.class.path=ext_classpath to the JVM startup parameter, you can call existing Java extension packages in python code.
4. Access JAVA system properties
Sometimes, some Java applications need to set or get system properties in the JVM.
Example of setting system variables when JVM starts:
Add the following parameters to the JVM startup parameters:
-Dproperty=value 4. Example
1. Call JAVA API directly
from jpype import *
import os.path
startJVM("C:/Java/jdk1.6.0 _10/jre/bin/client/jvm.dll", "-ea")
java.lang.System.out.println("hello World")
shutdownJVM() 2. Call JAVA third-party extension package
1) JAVA custom third-party jar package: package the JpypeDemo class into a jpypedemo.jar file and store it in the F:/sample_Py directory
package jpype;
public class JpypeDemo {
public String sayHello(String user){
return "hello" + user;
}
public int calc(int a, int b){
return a + b;
}
} 2) Python Call third-party JAVA jar package program
from jpype import *
import os.path
jarpath = os.path.join(os.path.abspath( '.'), 'F:/sample_Py/')
startJVM("C:/Java/jdk1.6.0_10/jre/bin/client/jvm.dll","-ea", " -Djava.class.path=%s" % (jarpath + 'jpypedemo.jar'))
#ubuntu startJVM("/home/geek/Android/jdk1.6.0_43/jre/lib/ i386/server/libjvm.so","-ea", "-Djava.class.path=%s" % (jarpath + 'XXX.jar'))
JDClass = JClass("jpype. JpypeDemo")
jd = JDClass()
#jd = JPackage("jpype").JpypeDemo() #Two methods of creating jd
jprint = java.lang.System.out.println
jprint(jd.sayHello("waw"))
jprint(jd.calc(2,4))
shutdownJVM()3. Access JAVA system properties
Assume that the property you want to set is named yourProperty and the property value is yourValue.
1) Example of setting system variables when JVM starts
import jpype
jvmPath = jpype.getDefaultJVMPath()
jvmArg = "- DyourProperty=yourValue ”
if not jpype.isJVMStarted():
jpype.startJVM(jvmPath, jvmArg)2) Example of setting system variables in the program
import jpype
prop = " yourProperty "
value = " yourValue "
system = jpype.JClass('java.lang.System')
system.setProperty(str(prop),str(value))3) Example of getting system variables in the program
import jpype
prop = " yourProperty "
system = jpype.JClass('java.lang.System')
value = system.getProperty(str(prop))