Geotools is a Java class library.

Geotools is a Java class library that provides many standard classes and methods to process spatial data. At the same time, this class library is built on the OGC standard and is an implementation of the OGC idea. OGC is an international standard, so geotools will surely become the main tool for open-source space data processing in the future. Most open-source software, such as udig and geoserver, processing spatial data is supported by geotools. Many other Web Services, command line tools, and desktop programs can be implemented by geotools.

Core features:
1. Define many interfaces for spatial concepts and data structures
1.1 Support for geometric topology is integrated through the JTs class library
1.2 attribute and spatial elements can be filtered using the OGC filter encoding Specification
2. Data Access APIs support element access, transaction support, and inter-thread locking
2.1 access to data and spatial databases in multiple formats
2.2 support multiple coordinate reference systems and their conversion
2.3 can work with extended map projection
2.4 data can be filtered and analyzed based on spatial and non-spatial attributes.
3. A stateless, low-memory rendering mechanism, especially in the server environment
3.1 construct and display a map using a complex style (SLD)
4. For the GML documents bound with XML schema, the powerful fourth-generation XML parsing technology gtxml is provided.
This parsing/encoding technology can be applied to the SLD, GML, filter, kml, and Se in the OGC standard. I personally think this is the core of geotools and a means for geotools to process large space data.
5. geotools plug-in: the open plug-in system allows you to add additional formats to the class library.
The ImageIO-ext plug-in allows geotools to read additional GRID formats from gdal.
6. geotools Extension
These space tools using core class libraries can provide additional building capabilities, such as swing, Brewer, and graph.
The extension module provides image and network support, verification, Web Map Server Resolution, parsing encoding XML and color Brewer (map plotting ).
7. geotools does not support
Geotools, as part of a broad community, can be used to incubate some new projects, focusing on Swing support, local and web processing support, adding additional symbols (symbology), and adding additional formats, generate a grid and implement ISO geometry.

Supported formats:
1. Supported raster format and data access
ArcSDE, arcgrid, geotiff, grassraster, gtopo30, image (JPEG, Tiff, GIF, PNG), ImageIO-ext-gdal, imagemoasaic, imagepyramid, jp2k, Matlab
2. Supported Database "JDBC-ng"
DB2, H2, MySQL, Oracle, postgis, spatialite, sqlserver
3. Supported vector formats and data access
App-schema, ArcSDE, CSV, DXF, edigeo, Excel, geojson, org, property, shapefile, WFS
4. xml binding
XML-based Java data structures and bindings provide the following formats: XSD-core (XML simple types), FeS, filter, gml2, gml3, kml, OWS, SLD, WCS, WFS, WMS, WPS, and VPF.
For extra geometry, SLD, and filter encoding and parsing, you can use Dom and sax programs.

Implementation criteria:
Supports most OGC standards
1. SLD/SE and rendering engine in OGC
2. General OGC element models include Simple Element support
3. Grid image expression of raster information in OGC
4. WFS, WMS, and additional WPS in OGC
5. ISO 19107 Geometry Specification