Stream example rendering to avoid OOM for large specs

docs/templating.md

@@ -813,6 +813,16 @@ Supporting files can either be processed through the templating engine or copied
 
 More variables can be found [here](https://github.com/OpenAPITools/openapi-generator/blob/master/modules/openapi-generator/src/main/java/org/openapitools/codegen/CodegenProperty.java).
 
+### Rendering Examples
+
+When rendering `example` values from `CodegenProperty` or `CodegenParameter` in Mustache templates, use `lambdaExample` instead of direct `example` interpolation:
+
+```mustache
+{{#hasExample}}{{#lambdaExample}}{{/lambdaExample}}{{/hasExample}}
+```
+
+The `example` field is still present for compatibility and scalar example values, but it is not a complete rendering API for templates. The `lambdaExample` section streams object and array examples as JSON while preserving scalar example rendering. This is a context-specific lambda on example-bearing objects, not an entry in the global `lambda` map. When embedding an example in a language string, JSON string, or HTML text context, wrap `lambdaExample` in the appropriate escaping lambda for that context, such as `lambda.escapeJavaString`, `lambda.escapeJsonString`, or `lambdaEscapeHtml`.
+
 
 ## Mustache Lambdas
 
@@ -829,10 +839,17 @@ Many generators (*those extending DefaultCodegen*) come with a small set of lamb
 - `forwardslash` - Replaces all occurrences of `\/`, `\` and `//` in a fragment by `/`.
 - `backslash` - Replaces all occurrences `/` in a fragment by `\`.
 - `doublequote` - Prepends `"` to the beginning and appends `"` to the end of a fragment.
+- `escapeJavaString` - Escapes fragment output for use inside Java-compatible string literals.
+- `escapeJsonString` - Escapes fragment output for use inside JSON string values.
 - `indented` - Prepends 4 spaces indention from second line of a fragment on. First line will be indented by Mustache.
 - `indented_8` - Prepends 8 spaces indention from second line of a fragment on. First line will be indented by Mustache.
 - `indented_12` - Prepends 12 spaces indention from second line of a fragment on. First line will be indented by Mustache.
 - `indented_16` -Prepends 16 spaces indention from second line of a fragment on. First line will be indented by Mustache.
+- `trim` - Removes leading and trailing whitespace from a fragment.
+- `trimLineBreaks` - Replaces duplicate line breaks in a fragment with a single line break.
+- `trimWhitespace` - Replaces duplicate whitespace in a fragment with a single space.
+- `trimTrailingWithNewLine` - Removes trailing whitespace from a fragment and appends a line break.
+- `trimTrailing` - Removes trailing whitespace from a fragment.
 
 Some generators provide additional lambdas. Lambda is invoked by `lambda.[lambda name]` expression. For example: `{{#lambda.lowercase}}FRAGMENT TO LOWERCASE{{/lambda.lowercase}}` to lower case text between `lambda.lowercase`.
 

docs/usage.md

@@ -487,7 +487,7 @@ OPTIONS
             variable templating of servers.
 
         --skip-operation-example
-            Skip examples defined in operations to avoid out of memory errors.
+            Skip examples defined in operations.
 
         --skip-validate-spec
             Skips the default behavior of validating an input specification.

modules/openapi-generator-core/src/main/java/org/openapitools/codegen/api/TemplatingEngineAdapter.java

@@ -19,6 +19,7 @@
 import java.io.FileInputStream;
 import java.io.IOException;
 import java.io.InputStream;
+import java.io.Writer;
 import java.nio.file.Path;
 import java.util.Arrays;
 import java.util.Locale;
@@ -67,6 +68,20 @@ default boolean handlesFile(String filename) {
     String compileTemplate(TemplatingExecutor executor, Map<String, Object> bundle,
                            String templateFile) throws IOException;
 
+    /**
+     * Writes a compiled template directly to a writer.
+     *
+     * @param executor     From where we can fetch the templates content (e.g. an instance of DefaultGenerator)
+     * @param bundle       The map of values to pass to the template
+     * @param templateFile The name of the template (e.g. model.mustache )
+     * @param writer       Destination writer for the processed template result
+     * @throws IOException an error occurred in the template processing
+     */
+    default void writeTemplate(TemplatingExecutor executor, Map<String, Object> bundle,
+                               String templateFile, Writer writer) throws IOException {
+        writer.write(compileTemplate(executor, bundle, templateFile));
+    }
+
     /**
      * Determines whether the template file with supported extensions exists. This may be on the filesystem,
      * external filesystem, or classpath (implementation is up to TemplatingGenerator).

modules/openapi-generator/src/main/java/org/openapitools/codegen/CodegenConstants.java

@@ -354,7 +354,7 @@ public static enum ENUM_PROPERTY_NAMING_TYPE {camelCase, PascalCase, snake_case,
     public static final String REMOVE_OPERATION_ID_PREFIX_COUNT_DESC = "Count of delimiter for the prefix. Use -1 for last Default: 1";
 
     public static final String SKIP_OPERATION_EXAMPLE = "skipOperationExample";
-    public static final String SKIP_OPERATION_EXAMPLE_DESC = "Skip examples defined in operations to avoid out of memory errors.";
+    public static final String SKIP_OPERATION_EXAMPLE_DESC = "Skip examples defined in operations.";
 
     public static final String STRIP_PACKAGE_NAME = "stripPackageName";
     public static final String STRIP_PACKAGE_NAME_DESC = "Whether to strip leading dot-separated packages from generated model classes";

modules/openapi-generator/src/main/java/org/openapitools/codegen/CodegenModel.java

@@ -18,10 +18,14 @@
 package org.openapitools.codegen;
 
 import com.fasterxml.jackson.annotation.JsonIgnoreProperties;
+import com.fasterxml.jackson.databind.JsonNode;
+import com.samskivert.mustache.Mustache;
+import io.swagger.v3.core.util.Json;
 import io.swagger.v3.oas.models.ExternalDocumentation;
 import lombok.Getter;
 import lombok.Setter;
 import org.apache.commons.lang3.StringUtils;
+import org.openapitools.codegen.templating.mustache.JsonOutputLambda;
 
 import java.util.*;
 
@@ -77,7 +81,10 @@ public class CodegenModel implements IJsonSchemaValidationProperties {
     @Getter @Setter
     public String title;
     @Getter @Setter
-    public String description, classVarName, modelJson, dataType, xmlPrefix, xmlNamespace, xmlName;
+    public String description, classVarName, dataType, xmlPrefix, xmlNamespace, xmlName;
+    @Getter
+    public String modelJson;
+    private JsonNode modelJsonValue;
     @Getter @Setter
     public String classFilename; // store the class file name, mainly used for import
     @Getter @Setter
@@ -274,6 +281,31 @@ public Map<String, Object> getExts() {
         return vendorExtensions;
     }
 
+    public Mustache.Lambda getLambdaModelJson() {
+        if (modelJsonValue != null) {
+            return new JsonOutputLambda(modelJsonValue);
+        }
+        if (modelJson != null) {
+            return new JsonOutputLambda(modelJson);
+        }
+        return null;
+    }
+
+    public void setModelJson(String modelJson) {
+        this.modelJson = modelJson;
+        this.modelJsonValue = null;
+    }
+
+    public void setModelJsonValue(Object modelJsonValue) {
+        this.modelJsonValue = modelJsonValue == null ? null : Json.mapper().valueToTree(modelJsonValue);
+        this.modelJson = null;
+    }
+
+    public void setModelJson(CodegenModel model) {
+        this.modelJsonValue = model.modelJsonValue;
+        this.modelJson = model.modelJson;
+    }
+
     @Override
     public CodegenProperty getContains() {
         return contains;

modules/openapi-generator/src/main/java/org/openapitools/codegen/CodegenOperation.java

@@ -56,8 +56,8 @@ public class CodegenOperation {
     public List<CodegenResponse> responses = new ArrayList<CodegenResponse>();
     public List<CodegenCallback> callbacks = new ArrayList<>();
     public Set<String> imports = new HashSet<String>();
-    public List<Map<String, String>> examples;
-    public List<Map<String, String>> requestBodyExamples;
+    public List<Map<String, Object>> examples;
+    public List<Map<String, Object>> requestBodyExamples;
     public ExternalDocumentation externalDocs;
     public Map<String, Object> vendorExtensions = new HashMap<String, Object>();
     public String nickname; // legacy support

modules/openapi-generator/src/main/java/org/openapitools/codegen/CodegenParameter.java

@@ -17,10 +17,14 @@
 
 package org.openapitools.codegen;
 
+import com.fasterxml.jackson.databind.JsonNode;
+import com.samskivert.mustache.Mustache;
 import io.swagger.v3.oas.models.examples.Example;
 import lombok.Getter;
 import lombok.Setter;
+import org.openapitools.codegen.templating.mustache.JsonOutputLambda;
 
+import java.math.BigDecimal;
 import java.util.*;
 
 /**
@@ -41,6 +45,7 @@ public class CodegenParameter implements IJsonSchemaValidationProperties {
     public String nameInPascalCase; // property name in pascal case (e.g. ModifiedDate)
     public String nameInSnakeCase; // property name in upper snake case
     public String example; // example value (x-example)
+    private JsonNode exampleJsonNode;
     public Map<String, Example> examples;
     public String jsonSchema;
     public boolean isString, isNumeric, isInteger, isLong, isNumber, isFloat, isDouble, isDecimal, isByteArray, isBinary,
@@ -184,6 +189,7 @@ public CodegenParameter copy() {
         output.defaultValue = this.defaultValue;
         output.enumDefaultValue = this.enumDefaultValue;
         output.example = this.example;
+        output.exampleJsonNode = this.exampleJsonNode;
         output.examples = this.examples;
         output.isEnum = this.isEnum;
         output.isEnumRef = this.isEnumRef;
@@ -392,6 +398,7 @@ public boolean equals(Object o) {
                 Objects.equals(isMatrix, that.isMatrix) &&
                 Objects.equals(isAllowEmptyValue, that.isAllowEmptyValue) &&
                 Objects.equals(example, that.example) &&
+                Objects.equals(exampleJsonNode, that.exampleJsonNode) &&
                 Objects.equals(examples, that.examples) &&
                 Objects.equals(jsonSchema, that.jsonSchema) &&
                 Objects.equals(_enum, that._enum) &&
@@ -543,6 +550,53 @@ public Map<String, Object> getExts() {
         return vendorExtensions;
     }
 
+    public Mustache.Lambda getLambdaExample() {
+        if (exampleJsonNode != null) {
+            if (exampleJsonNode.isValueNode()) {
+                return new JsonOutputLambda(exampleJsonNode.asText());
+            }
+            return new JsonOutputLambda(exampleJsonNode);
+        }
+        if (example != null) {
+            return new JsonOutputLambda(example);
+        }
+        return null;
+    }
+
+    public Mustache.Lambda getLambdaExampleJsonLiteral() {
+        if (exampleJsonNode != null) {
+            return new JsonOutputLambda(exampleJsonNode);
+        }
+        if (example == null) {
+            return null;
+        }
+        if (isBoolean) {
+            return new JsonOutputLambda(Boolean.valueOf(example));
+        }
+        if (isNumeric || isInteger || isLong || isNumber || isFloat || isDouble || isDecimal || isShort || isUnboundedInteger) {
+            try {
+                return new JsonOutputLambda(new BigDecimal(example));
+            } catch (NumberFormatException e) {
+                return new JsonOutputLambda((Object) example);
+            }
+        }
+        return new JsonOutputLambda((Object) example);
+    }
+
+    public boolean getHasExample() {
+        return exampleJsonNode != null || example != null;
+    }
+
+    public void setExample(String example) {
+        this.example = example;
+        this.exampleJsonNode = null;
+    }
+
+    public void setExample(JsonNode exampleJsonNode) {
+        this.exampleJsonNode = exampleJsonNode;
+        this.example = exampleJsonNode != null && exampleJsonNode.isValueNode() ? exampleJsonNode.asText() : null;
+    }
+
     // use schema.getContains or content.mediaType.schema.getContains instead of this
     @Override
     public CodegenProperty getContains() {
@@ -1151,4 +1205,3 @@ public void setIsEnum(boolean isEnum) {
         this.isEnum = isEnum;
     }
 }
-

modules/openapi-generator/src/main/java/org/openapitools/codegen/CodegenProperty.java

@@ -17,8 +17,11 @@
 
 package org.openapitools.codegen;
 
+import com.fasterxml.jackson.databind.JsonNode;
+import com.samskivert.mustache.Mustache;
 import lombok.Getter;
 import lombok.Setter;
+import org.openapitools.codegen.templating.mustache.JsonOutputLambda;
 
 import java.util.*;
 
@@ -96,8 +99,9 @@ public class CodegenProperty implements Cloneable, IJsonSchemaValidationProperti
     /**
      * A free-form property to include an example of an instance for this schema.
      */
-    @Getter @Setter
+    @Getter
     public String example;
+    private JsonNode exampleJsonNode;
 
     @Getter @Setter
     public String jsonSchema;
@@ -605,6 +609,33 @@ public String getRef() {
         return ref;
     }
 
+    public Mustache.Lambda getLambdaExample() {
+        if (exampleJsonNode != null) {
+            if (exampleJsonNode.isValueNode()) {
+                return new JsonOutputLambda(exampleJsonNode.asText());
+            }
+            return new JsonOutputLambda(exampleJsonNode);
+        }
+        if (example != null) {
+            return new JsonOutputLambda(example);
+        }
+        return null;
+    }
+
+    public boolean getHasExample() {
+        return exampleJsonNode != null || example != null;
+    }
+
+    public void setExample(String example) {
+        this.example = example;
+        this.exampleJsonNode = null;
+    }
+
+    public void setExample(JsonNode exampleJsonNode) {
+        this.exampleJsonNode = exampleJsonNode;
+        this.example = exampleJsonNode != null && exampleJsonNode.isValueNode() ? exampleJsonNode.asText() : null;
+    }
+
     @Override
     public CodegenProperty clone() {
         try {
@@ -651,6 +682,7 @@ public CodegenProperty clone() {
             if (this.contains != null) {
                 cp.setContains(this.contains);
             }
+            cp.exampleJsonNode = this.exampleJsonNode;
 
             return cp;
         } catch (CloneNotSupportedException e) {
@@ -1183,6 +1215,7 @@ public boolean equals(Object o) {
                 Objects.equals(minLength, that.minLength) &&
                 Objects.equals(pattern, that.pattern) &&
                 Objects.equals(example, that.example) &&
+                Objects.equals(exampleJsonNode, that.exampleJsonNode) &&
                 Objects.equals(jsonSchema, that.jsonSchema) &&
                 Objects.equals(minimum, that.minimum) &&
                 Objects.equals(maximum, that.maximum) &&