Proj4J not precise for EPSG:3857 transformations

You have a problem with your code, because in Python with pyproj (python interface to PROJ4 library)

from pyproj import Proj, transform
inProj  = Proj("+init=EPSG:31469")
outProj = Proj("+init=EPSG:3857")
x1,y1 =  (5439627.33,5661628.09)
x2,y2 =transform(inProj,outProj,x1,y1)
x3,y3 =  transform(outProj,inProj,x2,y2)
print x1,y1
5439627.33 5661628.09
print x2,y2
1573657.37085 6636624.40597
print x3,y3
5439627.33052 5661628.09049

The core of the library OSGEO Proj4J is a port of the ​PROJ.4 C library and it is specified that:

Status: Currently this library is still being created, and is not yet ready for download

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