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Feature (template): Supports multi character template separators #3801

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8c1dc4a
Feature (template): Supports multi character template separators
zjxzjw Jul 12, 2025
f286e91
Refactor (spring ai template st): Optimize template rendering logic
zjxzjw Jul 15, 2025
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4 changes: 2 additions & 2 deletions ...nt-chat/src/test/java/org/springframework/ai/chat/client/DefaultChatClientUtilsTests.java
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Original file line number Diff line number Diff line change
Expand Up @@ -342,8 +342,8 @@ void whenCustomTemplateRendererIsProvidedThenItIsUsedForRendering() {
String systemText = "Instructions <name>";
Map<String, Object> systemParams = Map.of("name", "Spring AI");
TemplateRenderer customRenderer = StTemplateRenderer.builder()
.startDelimiterToken('<')
.endDelimiterToken('>')
.startDelimiterToken("<")
.endDelimiterToken(">")
.build();
ChatModel chatModel = mock(ChatModel.class);
DefaultChatClient.DefaultChatClientRequestSpec inputRequest = (DefaultChatClient.DefaultChatClientRequestSpec) ChatClient
Expand Down
195 changes: 104 additions & 91 deletions ...g-ai-template-st/src/main/java/org/springframework/ai/template/st/StTemplateRenderer.java
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Original file line number Diff line number Diff line change
@@ -1,12 +1,12 @@
/*
/**
* Copyright 2023-2025 the original author or authors.
*
* <p>
* Licensed under the Apache License, Version 2.0 (the "License");
* you may not use this file except in compliance with the License.
* You may obtain a copy of the License at
*
* <p>
* https://www.apache.org/licenses/LICENSE-2.0
*
* <p>
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
Expand All @@ -16,16 +16,20 @@

package org.springframework.ai.template.st;

import java.util.Collections;
import java.util.HashSet;
import java.util.Map;
import java.util.Set;
import java.util.regex.Matcher;
import java.util.regex.Pattern;

import org.antlr.runtime.Token;
import org.antlr.runtime.TokenStream;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;
import org.stringtemplate.v4.ST;
import org.stringtemplate.v4.compiler.Compiler;
import org.stringtemplate.v4.compiler.STException;
import org.stringtemplate.v4.compiler.STLexer;

import org.springframework.ai.template.TemplateRenderer;
Expand Down Expand Up @@ -57,106 +61,126 @@ public class StTemplateRenderer implements TemplateRenderer {

private static final String VALIDATION_MESSAGE = "Not all variables were replaced in the template. Missing variable names are: %s.";

private static final char DEFAULT_START_DELIMITER_TOKEN = '{';
private static final String DEFAULT_START_DELIMITER = "{";

private static final char DEFAULT_END_DELIMITER_TOKEN = '}';
private static final String DEFAULT_END_DELIMITER = "}";

private static final ValidationMode DEFAULT_VALIDATION_MODE = ValidationMode.THROW;

private static final boolean DEFAULT_VALIDATE_ST_FUNCTIONS = false;

private final char startDelimiterToken;
private final String startDelimiterToken;

private final char endDelimiterToken;
private final String endDelimiterToken;

private final ValidationMode validationMode;

private final boolean validateStFunctions;

/**
* Constructs a new {@code StTemplateRenderer} with the specified delimiter tokens,
* validation mode, and function validation flag.
* @param startDelimiterToken the character used to denote the start of a template
* variable (e.g., '{')
* @param endDelimiterToken the character used to denote the end of a template
* variable (e.g., '}')
* @param validationMode the mode to use for template variable validation; must not be
* null
* @param validateStFunctions whether to validate StringTemplate functions in the
* template
* Constructs a StTemplateRenderer with custom delimiters, validation mode, and
* function validation flag.
* @param startDelimiterToken Multi-character start delimiter (non-null/non-empty)
* @param endDelimiterToken Multi-character end delimiter (non-null/non-empty)
* @param validationMode Mode for handling missing variables (non-null)
* @param validateStFunctions Whether to treat ST built-in functions as variables
*/
public StTemplateRenderer(char startDelimiterToken, char endDelimiterToken, ValidationMode validationMode,
public StTemplateRenderer(String startDelimiterToken, String endDelimiterToken, ValidationMode validationMode,
boolean validateStFunctions) {
Assert.notNull(validationMode, "validationMode cannot be null");
Assert.notNull(validationMode, "validationMode must not be null");
Assert.hasText(startDelimiterToken, "startDelimiterToken must not be null or empty");
Assert.hasText(endDelimiterToken, "endDelimiterToken must not be null or empty");

this.startDelimiterToken = startDelimiterToken;
this.endDelimiterToken = endDelimiterToken;
this.validationMode = validationMode;
this.validateStFunctions = validateStFunctions;
}

/**
* Renders the template by first converting custom delimiters to ST's native format,
* then replacing variables.
* @param template Template string with variables (non-null/non-empty)
* @param variables Map of variable names to values (non-null, keys must not be null)
* @return Rendered string with variables replaced
*/
@Override
public String apply(String template, Map<String, Object> variables) {
Assert.hasText(template, "template cannot be null or empty");
Assert.notNull(variables, "variables cannot be null");
Assert.noNullElements(variables.keySet(), "variables keys cannot be null");
Assert.hasText(template, "template must not be null or empty");
Assert.notNull(variables, "variables must not be null");
Assert.noNullElements(variables.keySet(), "variables keys must not contain null");

try {
String processedTemplate = preprocessTemplate(template);
ST st = new ST(processedTemplate, '{', '}');
variables.forEach(st::add);

ST st = createST(template);
for (Map.Entry<String, Object> entry : variables.entrySet()) {
st.add(entry.getKey(), entry.getValue());
if (validationMode != ValidationMode.NONE) {
validate(st, variables);
}

return st.render();
}
if (this.validationMode != ValidationMode.NONE) {
validate(st, variables);
catch (STException e) {
throw new IllegalArgumentException("Failed to render template", e);
}
return st.render();
}

private ST createST(String template) {
try {
return new ST(template, this.startDelimiterToken, this.endDelimiterToken);
}
catch (Exception ex) {
throw new IllegalArgumentException("The template string is not valid.", ex);
/**
* Converts custom delimiter-wrapped variables (e.g., <name>) to ST's native format
* ({name}).
*/
private String preprocessTemplate(String template) {
if ("{".equals(startDelimiterToken) && "}".equals(endDelimiterToken)) {
return template;
}
String escapedStart = Pattern.quote(startDelimiterToken);
String escapedEnd = Pattern.quote(endDelimiterToken);
String variablePattern = escapedStart + "([a-zA-Z_][a-zA-Z0-9_]*)" + escapedEnd;
return template.replaceAll(variablePattern, "{$1}");
}

/**
* Validates that all required template variables are provided in the model. Returns
* the set of missing variables for further handling or logging.
* @param st the StringTemplate instance
* @param templateVariables the provided variables
* @return set of missing variable names, or empty set if none are missing
* Validates that all template variables have been provided in the variables map.
*/
private Set<String> validate(ST st, Map<String, Object> templateVariables) {
private void validate(ST st, Map<String, Object> templateVariables) {
Set<String> templateTokens = getInputVariables(st);
Set<String> modelKeys = templateVariables != null ? templateVariables.keySet() : new HashSet<>();
Set<String> modelKeys = templateVariables != null ? templateVariables.keySet() : Collections.emptySet();
Set<String> missingVariables = new HashSet<>(templateTokens);
missingVariables.removeAll(modelKeys);

if (!missingVariables.isEmpty()) {
if (this.validationMode == ValidationMode.WARN) {
logger.warn(VALIDATION_MESSAGE.formatted(missingVariables));
String message = VALIDATION_MESSAGE.formatted(missingVariables);
if (validationMode == ValidationMode.WARN) {
logger.warn(message);
}
else if (this.validationMode == ValidationMode.THROW) {
throw new IllegalStateException(VALIDATION_MESSAGE.formatted(missingVariables));
else if (validationMode == ValidationMode.THROW) {
throw new IllegalStateException(message);
}
}
return missingVariables;
}

/**
* Extracts variable names from the template using ST's token stream and regex
* validation.
*/
private Set<String> getInputVariables(ST st) {
TokenStream tokens = st.impl.tokens;
Set<String> inputVariables = new HashSet<>();
TokenStream tokens = st.impl.tokens;
boolean isInsideList = false;

// StringTemplate 控制结构关键字集合，校验时忽略它们
Set<String> stKeywords = Set.of("if", "elseif", "else", "endif", "for", "endfor", "while", "endwhile", "switch",
"endswitch", "case", "default");

for (int i = 0; i < tokens.size(); i++) {
Token token = tokens.get(i);

// Handle list variables with option (e.g., {items; separator=", "})
if (token.getType() == STLexer.LDELIM && i + 1 < tokens.size()
&& tokens.get(i + 1).getType() == STLexer.ID) {
if (i + 2 < tokens.size() && tokens.get(i + 2).getType() == STLexer.COLON) {
String text = tokens.get(i + 1).getText();
if (!Compiler.funcs.containsKey(text) || this.validateStFunctions) {
if ((!Compiler.funcs.containsKey(text) || validateStFunctions) && !stKeywords.contains(text)) {
inputVariables.add(text);
isInsideList = true;
}
Expand All @@ -165,34 +189,46 @@ private Set<String> getInputVariables(ST st) {
else if (token.getType() == STLexer.RDELIM) {
isInsideList = false;
}
// Only add IDs that are not function calls (i.e., not immediately followed by
else if (!isInsideList && token.getType() == STLexer.ID) {
boolean isFunctionCall = (i + 1 < tokens.size() && tokens.get(i + 1).getType() == STLexer.LPAREN);
boolean isDotProperty = (i > 0 && tokens.get(i - 1).getType() == STLexer.DOT);
// Only add as variable if:
// - Not a function call
// - Not a built-in function used as property (unless validateStFunctions)
if (!isFunctionCall && (!Compiler.funcs.containsKey(token.getText()) || this.validateStFunctions
|| !(isDotProperty && Compiler.funcs.containsKey(token.getText())))) {
inputVariables.add(token.getText());
String tokenText = token.getText();
if (!isFunctionCall && (!Compiler.funcs.containsKey(tokenText) || validateStFunctions
|| !(isDotProperty && Compiler.funcs.containsKey(tokenText)))) {
if (!stKeywords.contains(tokenText)) {
inputVariables.add(tokenText);
}
}
}
}

Pattern varPattern = Pattern.compile(Pattern.quote("{") + "([a-zA-Z_][a-zA-Z0-9_]*)" + Pattern.quote("}"));
Matcher matcher = varPattern.matcher(st.impl.template);
while (matcher.find()) {
String var = matcher.group(1);
if (!stKeywords.contains(var)) {
inputVariables.add(var);
}
}

return inputVariables;
}

/**
* Creates a builder for configuring StTemplateRenderer instances.
*/
public static Builder builder() {
return new Builder();
}

/**
* Builder for configuring and creating {@link StTemplateRenderer} instances.
* Builder for fluent configuration of StTemplateRenderer.
*/
public static final class Builder {

private char startDelimiterToken = DEFAULT_START_DELIMITER_TOKEN;
private String startDelimiterToken = DEFAULT_START_DELIMITER;

private char endDelimiterToken = DEFAULT_END_DELIMITER_TOKEN;
private String endDelimiterToken = DEFAULT_END_DELIMITER;

private ValidationMode validationMode = DEFAULT_VALIDATION_MODE;

Expand All @@ -202,65 +238,42 @@ private Builder() {
}

/**
* Sets the character used as the start delimiter for template expressions.
* Default is '{'.
* @param startDelimiterToken The start delimiter character.
* @return This builder instance for chaining.
* Sets the multi-character start delimiter (e.g., "{{" or "<").
*/
public Builder startDelimiterToken(char startDelimiterToken) {
public Builder startDelimiterToken(String startDelimiterToken) {
this.startDelimiterToken = startDelimiterToken;
return this;
}

/**
* Sets the character used as the end delimiter for template expressions. Default
* is '}'.
* @param endDelimiterToken The end delimiter character.
* @return This builder instance for chaining.
* Sets the multi-character end delimiter (e.g., "}}" or ">").
*/
public Builder endDelimiterToken(char endDelimiterToken) {
public Builder endDelimiterToken(String endDelimiterToken) {
this.endDelimiterToken = endDelimiterToken;
return this;
}

/**
* Sets the validation mode to control behavior when the provided variables do not
* match the variables required by the template. Default is
* {@link ValidationMode#THROW}.
* @param validationMode The desired validation mode.
* @return This builder instance for chaining.
* Sets the validation mode for missing variables.
*/
public Builder validationMode(ValidationMode validationMode) {
this.validationMode = validationMode;
return this;
}

/**
* Configures the renderer to support StringTemplate's built-in functions during
* validation.
* <p>
* When enabled (set to true), identifiers in the template that match known ST
* function names (e.g., "first", "rest", "length") will not be treated as
* required input variables during validation.
* <p>
* When disabled (default, false), these identifiers are treated like regular
* variables and must be provided in the input map if validation is enabled
* ({@link ValidationMode#WARN} or {@link ValidationMode#THROW}).
* @return This builder instance for chaining.
* Enables validation of ST built-in functions (treats them as variables).
*/
public Builder validateStFunctions() {
this.validateStFunctions = true;
return this;
}

/**
* Builds and returns a new {@link StTemplateRenderer} instance with the
* configured settings.
* @return A configured {@link StTemplateRenderer}.
* Builds the configured StTemplateRenderer instance.
*/
public StTemplateRenderer build() {
return new StTemplateRenderer(this.startDelimiterToken, this.endDelimiterToken, this.validationMode,
this.validateStFunctions);
return new StTemplateRenderer(startDelimiterToken, endDelimiterToken, validationMode, validateStFunctions);
}

}
Expand Down
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