Python橋接Java工具JPype

JPype這玩意可以橋接Java,在Python中調用Java的類，比較好用，對外介面不多，不過需要注意的是python和java類型匹配的問題.可以參考官方文檔

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

過程中遇到個小問題，設定classpath時，-D前面留了一個空格，導致始終找不到類的錯誤，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	I (1)	I (1)	X	I			X (10)
long	I (1)	I (1)	I (1)	X
float					I (1)	X
sequence
dictionary
string								I (2)	X
unicode								I (2)	X
JByte	X
JShort		X
JInt			X
JLong				X
JFloat					X
JDouble						X
JBoolean							X
JString									X		I (3)
JChar								X
JArray										I/X (4)	I (5)
JObject										I/X (6)	I/X (7)
JavaObject											I (8)
JavaClass											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.