freemarker-generator-cli/src/site/markdown/cli/concepts/data-sources.md

DataSources

A DataSource consists of lazy-loaded data available in Apache FreeMarker's model (context) - it provides

a charset for reading textual content
a content type
a name and a group
access to textual content directly or using a line iterator
access to the data input stream

Loading A DataSource

A DataSource can be loaded from the file system, e.g. as positional command line argument

bin/freemarker-cli -t templates/info.ftl README.md

FreeMarker CLI DataSources
------------------------------------------------------------------------------
    [#1], name=README.md, group=default, contentType=text/markdown, charset=UTF-8, length=57,188 Bytes
    URI : file:/Users/sgoeschl/work/github/apache/freemarker-generator/freemarker-generator-cli/target/appassembler/README.md

from an URL

bin/freemarker-cli --data-source xkcd=https://xkcd.com/info.0.json -t templates/info.ftl

FreeMarker CLI DataSources
------------------------------------------------------------------------------
    [#1], name=xkcd, group=default, contentType=application/json, charset=UTF-8, length=-1 Bytes
    URI : https://xkcd.com/info.0.json

or from an environment variable, e.g. NGINX_CONF having a JSON payload

export NGINX_CONF='{"NGINX_PORT":"8443","NGINX_HOSTNAME":"localhost"}'
bin/freemarker-cli -t templates/info.ftl -s conf=env:///NGINX_CONF#mimetype=application/json

FreeMarker CLI DataSources
------------------------------------------------------------------------------
    [#1], name=conf, group=default, contentType=application/json, charset=UTF-8, length=50 Bytes
    URI : env:///NGINX_CONF

Of course you can load multiple DataSources directly

bin/freemarker-cli -t templates/info.ftl README.md xkcd=https://xkcd.com/info.0.json
 
FreeMarker CLI DataSources
------------------------------------------------------------------------------
    [#1], name=README.md, group=default, contentType=text/markdown, charset=UTF-8, length=57,188 Bytes
    URI : file:/Users/sgoeschl/work/github/apache/freemarker-generator/freemarker-generator-cli/target/appassembler/README.md
    [#2], name=xkcd, group=default, contentType=application/json, charset=UTF-8, length=-1 Bytes
    URI : https://xkcd.com/info.0.json

or load them from a directory

bin/freemarker-cli -t templates/info.ftl -s site/sample/
FreeMarker CLI DataSources
------------------------------------------------------------------------------
    [#1], name=combined-access.log, group=default, contentType=text/plain, charset=UTF-8, length=2,068 Bytes
    URI : file:/Users/sgoeschl/work/github/apache/freemarker-generator/freemarker-generator-cli/target/appassembler/site/sample/accesslog/combined-access.log
    ...
    [#22], name=swagger-spec.yaml, group=default, contentType=text/yaml, charset=UTF-8, length=17,555 Bytes
    URI : file:/Users/sgoeschl/work/github/apache/freemarker-generator/freemarker-generator-cli/target/appassembler/site/sample/yaml/swagger-spec.yaml

which can be combined with include and exclude filters

bin/freemarker-cli -t templates/info.ftl -s site/sample --data-source-include=*.json

FreeMarker CLI DataSources
------------------------------------------------------------------------------
    [#1], name=github-users.json, group=default, contentType=application/json, charset=UTF-8, length=7,168 Bytes
    URI : file:/Users/sgoeschl/work/github/apache/freemarker-generator/freemarker-generator-cli/target/appassembler/site/sample/json/github-users.json
    [#2], name=swagger-spec.json, group=default, contentType=application/json, charset=UTF-8, length=24,948 Bytes
    URI : file:/Users/sgoeschl/work/github/apache/freemarker-generator/freemarker-generator-cli/target/appassembler/site/sample/json/swagger-spec.json