Resolve placeholders at map level before YAML/JSON serialization by gabrielschulhof · Pull Request #3235 · spring-cloud/spring-cloud-config

gabrielschulhof · 2026-05-22T22:47:38Z

Instead of resolving placeholders by string-manipulating serialized YAML/JSON output, resolve them in the property Map before passing to the serializer. This lets SnakeYAML and Jackson handle multiline values and escaping natively, eliminating the need for:

OutputFormat enum
resolveYamlPlaceholders / resolveAsBlockScalar / isStandalonePlaceholder
resolvePlaceholdersWithTransform with JsonStringEncoder
joinMultiLinePlaceholders

Add resolveMapPlaceholders() which recursively walks Maps and Lists, resolving ${...} in String values via PropertyPlaceholderHelper with key trimming (handles SnakeYAML-folded multi-line placeholders).

The text-based resolvePlaceholders() remains for .properties output.

Re: #3234

Copilot

Pull request overview

This PR fixes invalid YAML/JSON emitted by the Config Server when resolving placeholders that expand to multiline values, by making placeholder resolution output-format aware.

Changes:

Introduces EnvironmentPropertySource.OutputFormat and a format-aware resolvePlaceholders(...) overload.
Updates EnvironmentController YAML/JSON endpoints to resolve placeholders using the appropriate format behavior (YAML block scalars, JSON newline escaping).
Adds unit/integration tests covering multiline placeholder expansion in YAML and JSON responses.

Reviewed changes

Copilot reviewed 4 out of 4 changed files in this pull request and generated 3 comments.

File	Description
spring-cloud-config-server/src/main/java/org/springframework/cloud/config/server/support/EnvironmentPropertySource.java	Adds `OutputFormat` and new YAML/JSON-specific placeholder resolution logic (block scalars / JSON escaping).
spring-cloud-config-server/src/main/java/org/springframework/cloud/config/server/environment/EnvironmentController.java	Routes YAML/JSON output through the new format-aware placeholder resolution.
spring-cloud-config-server/src/test/java/org/springframework/cloud/config/server/support/EnvironmentPropertySourceTest.java	Adds focused unit tests for YAML block scalar and JSON escaping behavior.
spring-cloud-config-server/src/test/java/org/springframework/cloud/config/server/environment/EnvironmentControllerTests.java	Adds controller-level tests verifying resolved multiline values round-trip correctly in YAML/JSON.

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ryanjbaxter · 2026-05-26T20:56:27Z

I think it would be better to try and resolve these placeholders before we convert it to a string.

For example in labelledYaml we could do something like

Map<String, Object> result = convertToMap(environment);
if (resolvePlaceholders) {
   resolveMapPlaceholders(result, prepareEnvironment(environment)); 
}
String yaml = new Yaml().dumpAsMap(result);

private static void resolveMapPlaceholders(Map<String, Object> map, StandardEnvironment env) {
    for (Map.Entry<String, Object> entry : map.entrySet()) {
        Object value = entry.getValue();
        if (value instanceof String) {
            entry.setValue(resolvePlaceholders(env, (String) value));
        } else if (value instanceof Map) {
            resolveMapPlaceholders((Map<String, Object>) value, env);
        } else if (value instanceof List) {
            resolveListPlaceholders((List<Object>) value, env);
        }
    }
}

gabrielschulhof · 2026-05-26T22:16:58Z

@ryanjbaxter I figured it would be better to do the resolution when the data is still structured, but I wasn't sure. Thanks for the steer!

ryanjbaxter

Could we add a test for default values (${key:default}) and ignoreUnresolvablePlaceholders=true with a key ${MISSING} in EnvironmentPropertySourceTest?

I think these changes should target the 4.3.x branch and I can merge it forward into main as well.

Instead of resolving placeholders by string-manipulating serialized YAML/JSON output, resolve them in the property Map before passing to the serializer. This lets SnakeYAML and Jackson handle multiline values and escaping natively, eliminating the need for: - OutputFormat enum - resolveYamlPlaceholders / resolveAsBlockScalar / isStandalonePlaceholder - resolvePlaceholdersWithTransform with JsonStringEncoder - joinMultiLinePlaceholders Add resolveMapPlaceholders() which recursively walks Maps and Lists, resolving ${...} in String values via PropertyPlaceholderHelper with key trimming (handles SnakeYAML-folded multi-line placeholders). The text-based resolvePlaceholders() remains for .properties output. Re: spring-cloud#3234 Signed-off-by: Gabriel Schulhof <gschulhof@auction.com>

Signed-off-by: Gabriel Schulhof <gschulhof@auction.com>

gabrielschulhof · 2026-05-27T17:23:55Z

@ryanjbaxter I have addressed your review comments. Please take another look!

ryanjbaxter · 2026-05-27T18:37:58Z

 public class EnvironmentPropertySource extends PropertySource<Environment> {

+	// Use PropertyPlaceholderHelper directly to trim whitespace from keys
+	private static final PropertyPlaceholderHelper helper = new PropertyPlaceholderHelper("${", "}", ":", null, true);


Please use snake yaml casing

@ryanjbaxter I'm sorry! I don't quite understand. Where should I use such casing?

Sorry I meant upper snake case, ie. PROPERTY_PLACEHOLDER_HELPER

Thanks for clarifying! Fixed.

ryanjbaxter · 2026-05-27T18:38:55Z

+
+		// Verify YAML is valid and values are resolved
+		Map<String, Object> reparsed = new Yaml().load(yaml);
+		java.util.List<Object> items = (java.util.List<Object>) reparsed.get("items");


Use imports

Sorry about that! Forgot to commit. These should all be using imports now.

ryanjbaxter · 2026-05-27T18:39:09Z

+	@Test
+	public void defaultValueUsedWhenKeyMissing() {
+		Environment environment = new Environment("test", "default");
+		java.util.Map<String, Object> map = new java.util.LinkedHashMap<>();


Use imports

ryanjbaxter · 2026-05-27T18:39:15Z

+		environment.add(new PropertySource("one", map));
+		StandardEnvironment prepared = prepareEnvironment(environment);
+
+		Map<String, Object> input = new java.util.LinkedHashMap<>();


Use imports

ryanjbaxter · 2026-05-27T18:39:20Z

+	@Test
+	public void defaultValueOverriddenWhenKeyExists() {
+		Environment environment = new Environment("test", "default");
+		java.util.Map<String, Object> map = new java.util.LinkedHashMap<>();


Use imports

ryanjbaxter · 2026-05-27T18:39:26Z

+		environment.add(new PropertySource("one", map));
+		StandardEnvironment prepared = prepareEnvironment(environment);
+
+		Map<String, Object> input = new java.util.LinkedHashMap<>();


Use imports

ryanjbaxter · 2026-05-27T18:39:31Z

+	@Test
+	public void unresolvablePlaceholderLeftIntact() {
+		Environment environment = new Environment("test", "default");
+		java.util.Map<String, Object> map = new java.util.LinkedHashMap<>();


Use imports

ryanjbaxter · 2026-05-27T18:39:37Z

+		environment.add(new PropertySource("one", map));
+		StandardEnvironment prepared = prepareEnvironment(environment);
+
+		Map<String, Object> input = new java.util.LinkedHashMap<>();


Use imports

Signed-off-by: Gabriel Schulhof <gschulhof@auction.com>

gabrielschulhof force-pushed the fix/yaml-multiline-placeholder-resolution branch from 026eebf to fdcede7 Compare May 22, 2026 22:48

spring-cloud-issues added the waiting-for-triage label May 22, 2026

ryanjbaxter requested a review from Copilot May 26, 2026 18:15

Copilot started reviewing on behalf of ryanjbaxter May 26, 2026 18:15 View session

Copilot AI reviewed May 26, 2026

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gabrielschulhof force-pushed the fix/yaml-multiline-placeholder-resolution branch from 28af6c1 to 655a49c Compare May 26, 2026 19:57

gabrielschulhof force-pushed the fix/yaml-multiline-placeholder-resolution branch 3 times, most recently from 5ced426 to e1e6556 Compare May 26, 2026 22:15

gabrielschulhof changed the title ~~Fix multiline placeholder resolution in YAML and JSON output~~ Resolve placeholders at map level before YAML/JSON serialization May 26, 2026

ryanjbaxter requested changes May 27, 2026

View reviewed changes

gabrielschulhof force-pushed the fix/yaml-multiline-placeholder-resolution branch from e1e6556 to b7ac585 Compare May 27, 2026 17:18

gabrielschulhof changed the base branch from main to 4.3.x May 27, 2026 17:19

address review comments

df93bd7

Signed-off-by: Gabriel Schulhof <gschulhof@auction.com>

gabrielschulhof force-pushed the fix/yaml-multiline-placeholder-resolution branch from b7ac585 to df93bd7 Compare May 27, 2026 17:19

ryanjbaxter requested changes May 27, 2026

View reviewed changes

gabrielschulhof added 2 commits May 27, 2026 13:09

Address more review comments

494baf0

Signed-off-by: Gabriel Schulhof <gschulhof@auction.com>

Address review comment

d227250

Signed-off-by: Gabriel Schulhof <gschulhof@auction.com>

ryanjbaxter merged commit c8364f7 into spring-cloud:4.3.x May 28, 2026
2 checks passed

ryanjbaxter linked an issue May 28, 2026 that may be closed by this pull request

Reference to multiline string rendered incorrectly in output #3234

Closed

gabrielschulhof deleted the fix/yaml-multiline-placeholder-resolution branch May 28, 2026 16:16

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ryanjbaxter commented May 26, 2026

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gabrielschulhof commented May 22, 2026 •

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