https://github.com/boundlessgeo/prj2epsg
GeoTools (Java GIS library) has several versions of the EPSG database available as JARs and you can use the CRS class to do lookups in both directions.
https://github.com/boundlessgeo/prj2epsg/blob/master/src/mai...
You may also be able to do a query on the SPATIAL_REF_SYS table in Postgres/PostGIS for what you want to do.
Hope this helps...