Python桥接Java工具JPype

JPype这玩意可以桥接Java,在Python中调用Java的类，比较好用，对外接口不多，不过需要注意的是python和java类型匹配的问题.可以参考官方文档

http://jpype.sourceforge.net/doc/user-guide/userguide.html

过程中遇到个小问题，设置classpath时，-D前面留了一个空格，导致始终找不到类的错误，很坑爹。

jvmArg = "-Djava.class.path=%s" % ext_classpath
jpype.startJVM(jvmpath,jvmArg)

JPype defines different leels of "match" between Python objects and Java types. These levels are :

• none, There is no way to convert.
• explicit (E), JPype canconvert ot the desired type, but only explicitly via the wrapper classes. This means the proper wrapper class will access this type as argument.
• implicit (I), JPype will convert as needed.
• exact> (X), Like implicit, but when deciding with method overload to use, one wj=here all the paramters match "exact" will take precedence over "implicit" matches.

byte

short

int

long

float

double

boolean

char

String

Array

Object

Class

int long float sequence dictionary string unicode JByte JShort JInt JLong JFloat JDouble JBoolean JString JChar JArray JObject JavaObject JavaClass

I (1)	I (1)	X	I			X (10)
I (1)	I (1)	I (1)	X
				I (1)	X
							I (2)	X
							I (2)	X
X
	X
		X
			X
				X
					X
						X
								X		I (3)
							X
									I/X (4)	I (5)
									I/X (6)	I/X (7)
										I (8)
										I (9)	X

(1) Conversion will occur if the Python value fits in the java native type.

(2) Conversion occurs if the python string or unicode is of length 1

(3) The required object must be of a type compatible with java.lang.String (java.lang.Object, java.util.Comparable)

(4) Number of dimensions must match, and the types must be compatible

(5) Only when the required type is java.lang.Object

(6) Only if the JObject wrapper's specified type is an compatible array class.

(7) Only if the required type is compatible with the wrappers's specified type. The actual type of the java object is not considered.

(8) Only if the requireds type is compatible with the Java Object actual type.

(9) Only when the required type is java.lang.Object or java.lang.Class

(10) only the values True and False are implitly converted to booleans.

Converting from java to python

The rules here are much simpler.

Java byte, short and int are converted to python int.

Java long are conversion to Python long

Java float and double are converted to python float.

Java boolean are converted to python int of value 1 or 0

Java char are converted to python unicode of length 1.

Java String are converteds to python unicode.

Java arrays are converteds to JArray

All other java object are converted to JavaObject.

Java Class are converted to JavaClass.

Java array Class are converted to JavaArrayClass.