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Read Java properties

The core reads and writes only YAML. Java .properties come from a sibling module, config-properties, which adds nothing to your dependency graph — a properties file is read with the standard library.

go get gitlab.com/phpboyscout/go/config-properties

import (
    "gitlab.com/phpboyscout/go/config"
    configproperties "gitlab.com/phpboyscout/go/config-properties"
)

store, err := config.NewStore(ctx,
    config.WithFiles(fsys, "/etc/app.yaml"),                               // YAML, the default
    config.WithBackend(configproperties.New(fsys, "/etc/app.properties")), // outranks it
)

Keys nest on dots

A properties key is dotted already, and each dot is a nesting separator:

server.host=localhost
server.port=8080

host := store.View().GetString("server.host") // "localhost"
port := store.View().GetInt("server.port")    // 8080

A properties layer therefore merges into a nested YAML or JSON one by the same paths. In Java a dotted key is a single flat string; here it nests, which is what makes it a configuration layer rather than a map.

The format it honours

key=value, key:value and key value are all separators; leading whitespace and whitespace around the separator is ignored; # and ! begin a comment; a line ending in an odd number of backslashes continues onto the next; and the standard escapes are recognised in keys and values — \t \n \r \f \\, an escaped separator or space, and \uXXXX.

Read-only

Values are strings; the read path casts. The format is read-only.

What it costs

Only the config graph — a .properties file is parsed with the standard library, so there is no parser module. An allowlist test in the module states it. No filesystem library: you supply the config.FS.