Java/Python互相调用

JPype

JPype is cross language bridge to allow Python programs full access to Java class libraries.

PyJnius

A Python module to access Java classes as Python classes using the Java Native Interface (JNI)

入门

pip install pyjnius

>>> from jnius import autoclass
>>> autoclass('java.lang.System').out.println('Hello world')
Hello world

>>> Stack = autoclass('java.util.Stack')
>>> stack = Stack()
>>> stack.push('hello')
>>> stack.push('world')
>>> print stack.pop()
world
>>> print stack.pop()
hello

Py4j

Py4J enables Python programs to dynamically access arbitrary Java objects, also enables Java programs to call back Python objects.

Python for Java，通过 socket 进行消息发送，使得 Python 中可以调用 Java代码 / Java 也可以回调Python对象。

入门

Java 端启动服务：

GatewayServer gatewayServer = new GatewayServer(new EntryPoint(), 25555);
gatewayServer.start();
System.out.println("Gateway Server Started");

Python端：

from py4j.java_gateway import JavaGateway, GatewayParameters

gateway = JavaGateway(gateway_parameters=GatewayParameters(port=25555))
# 获取String类型
JString = gateway.jvm.java.lang.String

# 转换成Python中的字符串
a = JString("213")

TODO: Java 回调 Python

序列化

net.razorvine.pickle(https://github.com/irmen/pickle)

Java and .NET library for Python's pickle serialization protocol

Apache Spark采用该库将Java对象序列化成Pickle格式，然后Python进行读取。

Java 读写 pickle （Python序列化格式）文件。

Pickle protocol version support:

• reading: 0,1,2,3,4,5;
• writing: 2.

Python to Java (unpickling)

PYTHON	JAVA
None	null
bool	boolean
int	int
long	long or BigInteger (depending on size)
string	String
unicode	String
complex	net.razorvine.pickle.objects.ComplexNumber
datetime.date	java.util.Calendar
datetime.datetime	java.util.Calendar
datetime.time	net.razorvine.pickle.objects.Time
datetime.timedelta	net.razorvine.pickle.objects.TimeDelta
float	double (float isn't used)
array.array	array of appropriate primitive type (char, int, short, long, float, double)
list	java.util.List
tuple	Object[]
set	java.util.Set
dict	java.util.Map
bytes	byte[]
bytearray	byte[]
decimal	BigDecimal
custom class	Map (dict with class attributes including its name in "class")
Pyro4.core.URI	net.razorvine.pyro.PyroURI
Pyro4.core.Proxy	net.razorvine.pyro.PyroProxy
Pyro4.errors.*	net.razorvine.pyro.PyroException
Pyro4.utils.flame.FlameBuiltin	net.razorvine.pyro.FlameBuiltin
Pyro4.utils.flame.FlameModule	net.razorvine.pyro.FlameModule
Pyro4.utils.flame.RemoteInteractiveConsole	net.razorvine.pyro.FlameRemoteConsole

Java to Python (pickling)

JAVA	PYTHON
null	None
boolean	bool
byte	int
char	str/unicode (length 1)
String	str/unicode
double	float
float	float
int	int
short	int
BigDecimal	decimal
BigInteger	long
any array	array if elements are primitive type (else tuple)
Object[]	tuple (cannot contain self-references)
byte[]	bytearray
java.util.Date	datetime.datetime
java.util.Calendar	datetime.datetime
java.sql.Date	datetime.date
java.sql.Time	datetime.time
java.sql.Timestamp	datetime.datetime
Enum	the enum value as string
java.util.Set	set
Map, Hashtable	dict
Vector, Collection	list
Serializable	treated as a JavaBean, see below.
JavaBean	dict of the bean's public properties + __class__ for the bean's type.
net.razorvine.pyro.PyroURI	Pyro4.core.URI
net.razorvine.pyro.PyroProxy	cannot be pickled.