diff --git a/pkgs/pkgs-lib/formats.nix b/pkgs/pkgs-lib/formats.nix
index 495a7094f9b4..6495b024b008 100644
--- a/pkgs/pkgs-lib/formats.nix
+++ b/pkgs/pkgs-lib/formats.nix
@@ -31,6 +31,9 @@ rec {
   */
 
 
+  inherit (import ./formats/java-properties/default.nix { inherit lib pkgs; })
+    javaProperties;
+
   json = {}: {
 
     type = with lib.types; let
diff --git a/pkgs/pkgs-lib/formats/java-properties/default.nix b/pkgs/pkgs-lib/formats/java-properties/default.nix
new file mode 100644
index 000000000000..e4f42a61f5c8
--- /dev/null
+++ b/pkgs/pkgs-lib/formats/java-properties/default.nix
@@ -0,0 +1,85 @@
+{ lib, pkgs }:
+{
+  javaProperties = {}: {
+    type = lib.types.attrsOf lib.types.str;
+
+    generate = name: value:
+      pkgs.runCommandLocal name
+        {
+          # Requirements
+          # ============
+          #
+          #  1. Strings in Nix carry over to the same
+          #     strings in Java => need proper escapes
+          #  2. Generate files quickly
+          #      - A JVM would have to match the app's
+          #        JVM to avoid build closure bloat
+          #      - Even then, JVM startup would slow
+          #        down config generation.
+          #
+          #
+          # Implementation
+          # ==============
+          #
+          # Escaping has two steps
+          #
+          # 1. jq
+          #    Escape known separators, in order not
+          #    to break up the keys and values.
+          #    This handles typical whitespace correctly,
+          #    but may produce garbage for other control
+          #    characters.
+          #
+          # 2. iconv
+          #    Escape >ascii code points to java escapes,
+          #    as .properties files are supposed to be
+          #    encoded in ISO 8859-1. It's an old format.
+          #    UTF-8 behavior may exist in some apps and
+          #    libraries, but we can't rely on this in
+          #    general.
+
+          passAsFile = [ "value" ];
+          value = builtins.toJSON value;
+          nativeBuildInputs = [
+            pkgs.jq
+            pkgs.libiconvReal
+          ];
+
+          jqCode =
+            let
+              main = ''
+                to_entries
+                  | .[]
+                  | "\(
+                      .key
+                      | ${commonEscapes}
+                      | gsub(" "; "\\ ")
+                      | gsub("="; "\\=")
+                    ) = \(
+                      .value
+                      | ${commonEscapes}
+                      | gsub("^ "; "\\ ")
+                      | gsub("\\n "; "\n\\ ")
+                    )"
+              '';
+              # Most escapes are equal for both keys and values.
+              commonEscapes = ''
+                gsub("\\\\"; "\\\\")
+                | gsub("\\n"; "\\n\\\n")
+                | gsub("#"; "\\#")
+                | gsub("!"; "\\!")
+                | gsub("\\t"; "\\t")
+                | gsub("\r"; "\\r")
+              '';
+            in
+            main;
+
+          inputEncoding = "UTF-8";
+
+        } ''
+        jq -r --arg hash '#' "$jqCode" "$valuePath" \
+          | iconv --from-code "$inputEncoding" --to-code JAVA \
+          > "$out"
+      '';
+  };
+}
diff --git a/pkgs/pkgs-lib/formats/java-properties/test/Main.java b/pkgs/pkgs-lib/formats/java-properties/test/Main.java
new file mode 100644
index 000000000000..dc83944f24b0
--- /dev/null
+++ b/pkgs/pkgs-lib/formats/java-properties/test/Main.java
@@ -0,0 +1,27 @@
+import java.io.FileInputStream;
+import java.io.InputStream;
+import java.util.Properties;
+import java.util.SortedSet;
+import java.util.TreeSet;
+
+class Main {
+    public static void main (String args[]) {
+        try {
+            InputStream input = new FileInputStream(args[0]);
+            Properties prop = new Properties();
+            prop.load(input);
+            SortedSet<String> keySet = new TreeSet(prop.keySet());
+            for (String key : keySet) {
+                System.out.println("KEY");
+                System.out.println(key);
+                System.out.println("VALUE");
+                System.out.println(prop.get(key));
+                System.out.println("");
+            }
+        } catch (Exception e) {
+          e.printStackTrace();
+          System.err.println(e.toString());
+          System.exit(1);
+        }
+    }
+}
diff --git a/pkgs/pkgs-lib/formats/java-properties/test/default.nix b/pkgs/pkgs-lib/formats/java-properties/test/default.nix
new file mode 100644
index 000000000000..4b3845c10296
--- /dev/null
+++ b/pkgs/pkgs-lib/formats/java-properties/test/default.nix
@@ -0,0 +1,85 @@
+{ fetchurl
+, formats
+, glibcLocales
+, jdk
+, lib
+, stdenv
+}:
+let
+  inherit (lib) concatStrings attrValues mapAttrs;
+
+  javaProperties = formats.javaProperties { };
+
+  input = {
+    foo = "bar";
+    "empty value" = "";
+    "typical.dot.syntax" = "com.sun.awt";
+    "" = "empty key's value";
+    "1" = "2 3";
+    "#" = "not a comment # still not";
+    "!" = "not a comment!";
+    "!a" = "still not! a comment";
+    "!b" = "still not ! a comment";
+    "dos paths" = "C:\\Program Files\\Nix For Windows\\nix.exe";
+    "a \t\nb" = " c";
+    "angry \t\nkey" = ''
+      multi
+      ${"\tline\r"}
+       space-
+        indented
+      trailing-space${" "}
+      trailing-space${"  "}
+      value
+    '';
+    "this=not" = "bad";
+    "nor = this" = "bad";
+    "all stuff" = "foo = bar";
+    "unicode big brain" = "e = mc□";
+    "ütf-8" = "dûh";
+    # NB: Some editors (vscode) show this _whole_ line in right-to-left order
+    "الجبر" = "أكثر من مجرد أرقام";
+  };
+
+in
+stdenv.mkDerivation {
+  name = "pkgs.formats.javaProperties-test-${jdk.name}";
+  nativeBuildInputs = [
+    jdk
+    glibcLocales
+  ];
+
+  # technically should go through the type.merge first, but that's tested
+  # in tests/formats.nix.
+  properties = javaProperties.generate "example.properties" input;
+
+  # Expected output as printed by Main.java
+  passAsFile = [ "expected" ];
+  expected = concatStrings (attrValues (
+    mapAttrs
+      (key: value:
+        ''
+          KEY
+          ${key}
+          VALUE
+          ${value}
+
+        ''
+      )
+      input
+  ));
+
+  src = lib.sourceByRegex ./. [
+    ".*\.java"
+  ];
+  LANG = "C.UTF-8";
+  buildPhase = ''
+    javac Main.java
+  '';
+  doCheck = true;
+  checkPhase = ''
+    cat -v $properties
+    java Main $properties >actual
+    diff -U3 $expectedPath actual
+  '';
+  installPhase = "touch $out";
+}
diff --git a/pkgs/pkgs-lib/tests/default.nix b/pkgs/pkgs-lib/tests/default.nix
index f3549ea9b0f2..ae91e15aa9ef 100644
--- a/pkgs/pkgs-lib/tests/default.nix
+++ b/pkgs/pkgs-lib/tests/default.nix
@@ -1,7 +1,45 @@
 # Call nix-build on this file to run all tests in this directory
-{ pkgs ? import ../../.. {} }:
+
+# This produces a link farm derivation with the original attrs
+# merged on top of it.
+# You can run parts of the "hierarchy" with for example:
+#     nix-build -A java-properties
+# See `structured` below.
+
+{ pkgs ? import ../../.. { } }:
 let
-  formats = import ./formats.nix { inherit pkgs; };
-in pkgs.linkFarm "nixpkgs-pkgs-lib-tests" [
-  { name = "formats"; path = import ./formats.nix { inherit pkgs; }; }
-]
+  inherit (pkgs.lib) mapAttrs mapAttrsToList isDerivation mergeAttrs foldl' attrValues recurseIntoAttrs;
+
+  structured = {
+    formats = import ./formats.nix { inherit pkgs; };
+    java-properties = recurseIntoAttrs {
+      jdk8 = pkgs.callPackage ../formats/java-properties/test { jdk = pkgs.jdk8; };
+      jdk11 = pkgs.callPackage ../formats/java-properties/test { jdk = pkgs.jdk11_headless; };
+      jdk17 = pkgs.callPackage ../formats/java-properties/test { jdk = pkgs.jdk17_headless; };
+    };
+  };
+
+  flatten = prefix: as:
+    foldl'
+      mergeAttrs
+      { }
+      (attrValues
+        (mapAttrs
+          (k: v:
+            if isDerivation v
+            then { "${prefix}${k}" = v; }
+            else if v?recurseForDerivations
+            then flatten "${prefix}${k}-" (removeAttrs v [ "recurseForDerivations" ])
+            else builtins.trace v throw "expected derivation or recurseIntoAttrs")
+          as
+        )
+      );
+in
+
+# It has to be a link farm for inclusion in the hydra unstable jobset.
+pkgs.linkFarm "pkgs-lib-formats-tests"
+  (mapAttrsToList
+    (k: v: { name = k; path = v; })
+    (flatten "" structured)
+  )
+// structured
diff --git a/pkgs/pkgs-lib/tests/formats.nix b/pkgs/pkgs-lib/tests/formats.nix
index 2bc4e407fe75..71b4a3946a34 100644
--- a/pkgs/pkgs-lib/tests/formats.nix
+++ b/pkgs/pkgs-lib/tests/formats.nix
@@ -168,4 +168,21 @@ in runBuildTests {
       level4 = "deep"
     '';
   };
+
+  # See also java-properties/default.nix for more complete tests
+  testJavaProperties = {
+    drv = evalFormat formats.javaProperties {} {
+      foo = "bar";
+      "1" = "2";
+      "ütf 8" = "dûh";
+      # NB: Some editors (vscode) show this _whole_ line in right-to-left order
+      "الجبر" = "أكثر من مجرد أرقام";
+    };
+    expected = ''
+      1 = 2
+      foo = bar
+      \u00fctf\ 8 = d\u00fbh
+      \u0627\u0644\u062c\u0628\u0631 = \u0623\u0643\u062b\u0631 \u0645\u0646 \u0645\u062c\u0631\u062f \u0623\u0631\u0642\u0627\u0645
+    '';
+  };
 }