[core][gradle] User-defined server variable substitutions (#3363)

* [core] Initial support for server variable overrides * [gradle] Support user overrides for serverVariables * [core] Clarify server variable overrides, and propagate them to templates in the "servers" array
2026-03-24 23:49:07 +00:00 · 2019-08-11 09:57:36 -04:00
parent 07381e7275
commit 06533b977c
29 changed files with 305 additions and 101 deletions
--- a/modules/openapi-generator/src/main/java/org/openapitools/codegen/CodegenConfig.java
+++ b/modules/openapi-generator/src/main/java/org/openapitools/codegen/CodegenConfig.java
@@ -43,6 +43,8 @@ public interface CodegenConfig {

    Map<String, Object> additionalProperties();

+    Map<String, String> serverVariableOverrides();
+
    Map<String, Object> vendorExtensions();

    String testPackage();
--- a/modules/openapi-generator/src/main/java/org/openapitools/codegen/CodegenServerVariable.java
+++ b/modules/openapi-generator/src/main/java/org/openapitools/codegen/CodegenServerVariable.java
@@ -7,4 +7,5 @@ public class CodegenServerVariable {
    public String defaultValue;
    public String description;
    public List<String> enumValues;
+    public String value;
 }
--- a/modules/openapi-generator/src/main/java/org/openapitools/codegen/DefaultCodegen.java
+++ b/modules/openapi-generator/src/main/java/org/openapitools/codegen/DefaultCodegen.java
@@ -97,6 +97,7 @@ public class DefaultCodegen implements CodegenConfig {
    protected String embeddedTemplateDir;
    protected String commonTemplateDir = "_common";
    protected Map<String, Object> additionalProperties = new HashMap<String, Object>();
+    protected Map<String, String> serverVariables = new HashMap<String, String>();
    protected Map<String, Object> vendorExtensions = new HashMap<String, Object>();
    protected List<SupportingFile> supportingFiles = new ArrayList<SupportingFile>();
    protected List<CliOption> cliOptions = new ArrayList<CliOption>();
@@ -503,12 +504,12 @@ public class DefaultCodegen implements CodegenConfig {
    public void postProcessParameter(CodegenParameter parameter) {
    }

-    //override with any special handling of the entire swagger spec
+    //override with any special handling of the entire OpenAPI spec document
    @SuppressWarnings("unused")
    public void preprocessOpenAPI(OpenAPI openAPI) {
    }

-    // override with any special handling of the entire swagger spec
+    // override with any special handling of the entire OpenAPI spec document
    @SuppressWarnings("unused")
    public void processOpenAPI(OpenAPI openAPI) {
    }
@@ -722,6 +723,10 @@ public class DefaultCodegen implements CodegenConfig {
        return additionalProperties;
    }

+    public Map<String, String> serverVariableOverrides() {
+        return serverVariables;
+    }
+
    public Map<String, Object> vendorExtensions() {
        return vendorExtensions;
    }
@@ -5053,14 +5058,34 @@ public class DefaultCodegen implements CodegenConfig {
        if (variables == null) {
            return Collections.emptyList();
        }
+
+        Map<String, String> variableOverrides = serverVariableOverrides();
+
        List<CodegenServerVariable> codegenServerVariables = new LinkedList<>();
        for (Entry<String, ServerVariable> variableEntry : variables.entrySet()) {
            CodegenServerVariable codegenServerVariable = new CodegenServerVariable();
            ServerVariable variable = variableEntry.getValue();
+            List<String> enums = variable.getEnum();
+
            codegenServerVariable.defaultValue = variable.getDefault();
            codegenServerVariable.description = escapeText(variable.getDescription());
-            codegenServerVariable.enumValues = variable.getEnum();
+            codegenServerVariable.enumValues = enums;
            codegenServerVariable.name = variableEntry.getKey();
+
+            // Sets the override value for a server variable pattern.
+            // NOTE: OpenAPI Specification doesn't prevent multiple server URLs with variables. If multiple objects have the same
+            //       variables pattern, user overrides will apply to _all_ of these patterns. We may want to consider indexed overrides.
+            if (variableOverrides != null && !variableOverrides.isEmpty()) {
+                String value = variableOverrides.getOrDefault(variableEntry.getKey(), variable.getDefault());
+                codegenServerVariable.value = value;
+
+                if (enums != null && !enums.isEmpty() && !enums.contains(value)) {
+                    LOGGER.warn("Variable override of '{}' is not listed in the enum of allowed values ({}).", value, StringUtils.join(enums, ","));
+                }
+            } else {
+                codegenServerVariable.value = variable.getDefault();
+            }
+
            codegenServerVariables.add(codegenServerVariable);
        }
        return codegenServerVariables;
--- a/modules/openapi-generator/src/main/java/org/openapitools/codegen/DefaultGenerator.java
+++ b/modules/openapi-generator/src/main/java/org/openapitools/codegen/DefaultGenerator.java
@@ -207,10 +207,12 @@ public class DefaultGenerator extends AbstractGenerator implements Generator {
            config.vendorExtensions().putAll(openAPI.getExtensions());
        }

-        URL url = URLPathUtils.getServerURL(openAPI);
+        // TODO: Allow user to define _which_ servers object in the array to target.
+        // Configures contextPath/basePath according to api document's servers
+        URL url = URLPathUtils.getServerURL(openAPI, config.serverVariableOverrides());
        contextPath = config.escapeText(url.getPath()).replaceAll("/$", ""); // for backward compatibility
        basePathWithoutHost = contextPath;
-        basePath = config.escapeText(URLPathUtils.getHost(openAPI)).replaceAll("/$", "");
+        basePath = config.escapeText(URLPathUtils.getHost(openAPI, config.serverVariableOverrides())).replaceAll("/$", "");
    }

    private void configureOpenAPIInfo() {
@@ -548,7 +550,7 @@ public class DefaultGenerator extends AbstractGenerator implements Generator {
                    }
                });
                Map<String, Object> operation = processOperations(config, tag, ops, allModels);
-                URL url = URLPathUtils.getServerURL(openAPI);
+                URL url = URLPathUtils.getServerURL(openAPI, config.serverVariableOverrides());
                operation.put("basePath", basePath);
                operation.put("basePathWithoutHost", config.encodePath(url.getPath()).replaceAll("/$", ""));
                operation.put("contextPath", contextPath);
@@ -819,7 +821,7 @@ public class DefaultGenerator extends AbstractGenerator implements Generator {
        Map<String, Object> apis = new HashMap<String, Object>();
        apis.put("apis", allOperations);

-        URL url = URLPathUtils.getServerURL(openAPI);
+        URL url = URLPathUtils.getServerURL(openAPI, config.serverVariableOverrides());

        bundle.put("openAPI", openAPI);
        bundle.put("basePath", basePath);
--- a/modules/openapi-generator/src/main/java/org/openapitools/codegen/config/CodegenConfigurator.java
+++ b/modules/openapi-generator/src/main/java/org/openapitools/codegen/config/CodegenConfigurator.java
@@ -67,6 +67,7 @@ public class CodegenConfigurator {
    private Map<String, String> importMappings = new HashMap<>();
    private Set<String> languageSpecificPrimitives = new HashSet<>();
    private Map<String, String> reservedWordMappings = new HashMap<>();
+    private Map<String, String> serverVariables = new HashMap<>();
    private String auth;

    public CodegenConfigurator() {
@@ -98,6 +99,12 @@ public class CodegenConfigurator {
        return null;
    }

+    public CodegenConfigurator addServerVariable(String key, String value) {
+        this.serverVariables.put(key, value);
+        generatorSettingsBuilder.withServerVariable(key, value);
+        return this;
+    }
+
    public CodegenConfigurator addAdditionalProperty(String key, Object value) {
        this.additionalProperties.put(key, value);
        generatorSettingsBuilder.withAdditionalProperty(key, value);
@@ -146,6 +153,18 @@ public class CodegenConfigurator {
        return this;
    }

+    public CodegenConfigurator setServerVariables(Map<String, String> serverVariables) {
+        this.serverVariables = serverVariables;
+        generatorSettingsBuilder.withServerVariables(serverVariables);
+        return this;
+    }
+
+    public CodegenConfigurator setReservedWordsMappings(Map<String, String> reservedWordMappings) {
+        this.reservedWordMappings = reservedWordMappings;
+        generatorSettingsBuilder.withReservedWordMappings(reservedWordMappings);
+        return this;
+    }
+
    public CodegenConfigurator setApiPackage(String apiPackage) {
        generatorSettingsBuilder.withApiPackage(apiPackage);
        return this;
@@ -247,6 +266,7 @@ public class CodegenConfigurator {

    public CodegenConfigurator setLanguageSpecificPrimitives(
            Set<String> languageSpecificPrimitives) {
+        this.languageSpecificPrimitives = languageSpecificPrimitives;
        generatorSettingsBuilder.withLanguageSpecificPrimitives(languageSpecificPrimitives);
        return this;
    }
@@ -296,12 +316,6 @@ public class CodegenConfigurator {
        return this;
    }

-    public CodegenConfigurator setReservedWordsMappings(Map<String, String> reservedWordMappings) {
-        this.reservedWordMappings = reservedWordMappings;
-        generatorSettingsBuilder.withReservedWordMappings(reservedWordMappings);
-        return this;
-    }
-
    public CodegenConfigurator setSkipOverwrite(boolean skipOverwrite) {
        workflowSettingsBuilder.withSkipOverwrite(skipOverwrite);
        return this;
@@ -459,6 +473,13 @@ public class CodegenConfigurator {
        config.reservedWordsMappings().putAll(generatorSettings.getReservedWordMappings());
        config.additionalProperties().putAll(generatorSettings.getAdditionalProperties());

+        Map<String, String> serverVariables = generatorSettings.getServerVariables();
+        if (!serverVariables.isEmpty()) {
+            // This is currently experimental due to vagueness in the specification
+            LOGGER.warn("user-defined server variable support is experimental.");
+            config.serverVariableOverrides().putAll(serverVariables);
+        }
+
        // any other additional properties?
        String templateDir = workflowSettings.getTemplateDir();
        if (templateDir != null) {
--- a/modules/openapi-generator/src/main/java/org/openapitools/codegen/config/CodegenConfiguratorUtils.java
+++ b/modules/openapi-generator/src/main/java/org/openapitools/codegen/config/CodegenConfiguratorUtils.java
@@ -107,6 +107,19 @@ public final class CodegenConfiguratorUtils {
        }
    }

+    public static void applyServerVariablesKvpList(List<String> values, CodegenConfigurator configurator) {
+        for(String value : values) {
+            applyServerVariablesKvp(value, configurator);
+        }
+    }
+
+    public static void applyServerVariablesKvp(String values, CodegenConfigurator configurator) {
+        final Map<String, String> map = createMapFromKeyValuePairs(values);
+        for (Map.Entry<String, String> entry : map.entrySet()) {
+            configurator.addServerVariable(entry.getKey(), entry.getValue());
+        }
+    }
+
    public static void applyLanguageSpecificPrimitivesCsvList(List<String> languageSpecificPrimitives, CodegenConfigurator configurator) {
        for(String propString : languageSpecificPrimitives) {
            applyLanguageSpecificPrimitivesCsv(propString, configurator);
--- a/modules/openapi-generator/src/main/java/org/openapitools/codegen/languages/AbstractCppCodegen.java
+++ b/modules/openapi-generator/src/main/java/org/openapitools/codegen/languages/AbstractCppCodegen.java
@@ -296,7 +296,7 @@ abstract public class AbstractCppCodegen extends DefaultCodegen implements Codeg

    @Override
    public void preprocessOpenAPI(OpenAPI openAPI) {
-        URL url = URLPathUtils.getServerURL(openAPI);
+        URL url = URLPathUtils.getServerURL(openAPI, serverVariableOverrides());
        String port = URLPathUtils.getPort(url, "");
        String host = url.getHost();
        if(!port.isEmpty()) {
--- a/modules/openapi-generator/src/main/java/org/openapitools/codegen/languages/AbstractJavaJAXRSServerCodegen.java
+++ b/modules/openapi-generator/src/main/java/org/openapitools/codegen/languages/AbstractJavaJAXRSServerCodegen.java
@@ -110,7 +110,7 @@ public abstract class AbstractJavaJAXRSServerCodegen extends AbstractJavaCodegen
        */

        if (!this.additionalProperties.containsKey(SERVER_PORT)) {
-            URL url = URLPathUtils.getServerURL(openAPI);
+            URL url = URLPathUtils.getServerURL(openAPI, serverVariableOverrides());
            // 8080 is the default value for a JEE Server:
            this.additionalProperties.put(SERVER_PORT, URLPathUtils.getPort(url, serverPort));
        }
--- a/modules/openapi-generator/src/main/java/org/openapitools/codegen/languages/AspNetCoreServerCodegen.java
+++ b/modules/openapi-generator/src/main/java/org/openapitools/codegen/languages/AspNetCoreServerCodegen.java
@@ -268,7 +268,7 @@ public class AspNetCoreServerCodegen extends AbstractCSharpCodegen {
    @Override
    public void preprocessOpenAPI(OpenAPI openAPI) {
        super.preprocessOpenAPI(openAPI);
-        URL url = URLPathUtils.getServerURL(openAPI);
+        URL url = URLPathUtils.getServerURL(openAPI, serverVariableOverrides());
        additionalProperties.put("serverHost", url.getHost());
        additionalProperties.put("serverPort", URLPathUtils.getPort(url, 8080));
    }
--- a/modules/openapi-generator/src/main/java/org/openapitools/codegen/languages/CSharpNancyFXServerCodegen.java
+++ b/modules/openapi-generator/src/main/java/org/openapitools/codegen/languages/CSharpNancyFXServerCodegen.java
@@ -359,7 +359,7 @@ public class CSharpNancyFXServerCodegen extends AbstractCSharpCodegen {

    @Override
    public void preprocessOpenAPI(final OpenAPI openAPI) {
-        URL url = URLPathUtils.getServerURL(openAPI);
+        URL url = URLPathUtils.getServerURL(openAPI, serverVariableOverrides());
        String path = URLPathUtils.getPath(url, "/");
        final String packageContextOption = (String) additionalProperties.get(PACKAGE_CONTEXT);
        additionalProperties.put("packageContext", packageContextOption == null ? sanitizeName(path) : packageContextOption);
--- a/modules/openapi-generator/src/main/java/org/openapitools/codegen/languages/FsharpGiraffeServerCodegen.java
+++ b/modules/openapi-generator/src/main/java/org/openapitools/codegen/languages/FsharpGiraffeServerCodegen.java
@@ -23,20 +23,14 @@ import org.openapitools.codegen.CodegenConstants;
 import org.openapitools.codegen.CodegenOperation;
 import org.openapitools.codegen.CodegenType;
 import org.openapitools.codegen.SupportingFile;
-import org.openapitools.codegen.CodegenModel;
-import org.openapitools.codegen.CodegenProperty;
 import org.openapitools.codegen.utils.URLPathUtils;
 import org.slf4j.Logger;
 import org.slf4j.LoggerFactory;

 import java.io.File;
 import java.net.URL;
-import java.util.Arrays;
 import java.util.Locale;
 import java.util.Map;
-import java.util.Set;
-import java.util.List;
-import java.util.ArrayList;

 import static java.util.UUID.randomUUID;

@@ -165,7 +159,7 @@ public class FsharpGiraffeServerCodegen extends AbstractFSharpCodegen {
    @Override
    public void preprocessOpenAPI(OpenAPI openAPI) {
        super.preprocessOpenAPI(openAPI);
-        URL url = URLPathUtils.getServerURL(openAPI);
+        URL url = URLPathUtils.getServerURL(openAPI, serverVariableOverrides());
        additionalProperties.put("serverHost", url.getHost());
        additionalProperties.put("serverPort", URLPathUtils.getPort(url, 8080));
    }
--- a/modules/openapi-generator/src/main/java/org/openapitools/codegen/languages/JavaPKMSTServerCodegen.java
+++ b/modules/openapi-generator/src/main/java/org/openapitools/codegen/languages/JavaPKMSTServerCodegen.java
@@ -538,7 +538,7 @@ public class JavaPKMSTServerCodegen extends AbstractJavaCodegen {
            additionalProperties.put(TITLE, this.title);
        }

-        URL url = URLPathUtils.getServerURL(openAPI);
+        URL url = URLPathUtils.getServerURL(openAPI, serverVariableOverrides());
        this.additionalProperties.put("serverPort", URLPathUtils.getPort(url, 8080));

        if (openAPI.getPaths() != null) {
--- a/modules/openapi-generator/src/main/java/org/openapitools/codegen/languages/JavaVertXServerCodegen.java
+++ b/modules/openapi-generator/src/main/java/org/openapitools/codegen/languages/JavaVertXServerCodegen.java
@@ -221,7 +221,7 @@ public class JavaVertXServerCodegen extends AbstractJavaCodegen {
        super.preprocessOpenAPI(openAPI);

        // add server port from the swagger file, 8080 by default
-        URL url = URLPathUtils.getServerURL(openAPI);
+        URL url = URLPathUtils.getServerURL(openAPI, serverVariableOverrides());
        this.additionalProperties.put("serverPort", URLPathUtils.getPort(url, 8080));

        // retrieve api version from swagger file, 1.0.0-SNAPSHOT by default
--- a/modules/openapi-generator/src/main/java/org/openapitools/codegen/languages/KotlinSpringServerCodegen.java
+++ b/modules/openapi-generator/src/main/java/org/openapitools/codegen/languages/KotlinSpringServerCodegen.java
@@ -407,7 +407,7 @@ public class KotlinSpringServerCodegen extends AbstractKotlinCodegen
        }

        if (!additionalProperties.containsKey(SERVER_PORT)) {
-            URL url = URLPathUtils.getServerURL(openAPI);
+            URL url = URLPathUtils.getServerURL(openAPI, serverVariableOverrides());
            this.additionalProperties.put(SERVER_PORT, URLPathUtils.getPort(url, 8080));
        }

--- a/modules/openapi-generator/src/main/java/org/openapitools/codegen/languages/NodeJSExpressServerCodegen.java
+++ b/modules/openapi-generator/src/main/java/org/openapitools/codegen/languages/NodeJSExpressServerCodegen.java
@@ -300,7 +300,7 @@ public class NodeJSExpressServerCodegen extends DefaultCodegen implements Codege

    @Override
    public void preprocessOpenAPI(OpenAPI openAPI) {
-        URL url = URLPathUtils.getServerURL(openAPI);
+        URL url = URLPathUtils.getServerURL(openAPI, serverVariableOverrides());
        String host =  URLPathUtils.getProtocolAndHost(url);
        String port = URLPathUtils.getPort(url, defaultServerPort) ;
        String basePath = url.getPath();
--- a/modules/openapi-generator/src/main/java/org/openapitools/codegen/languages/NodeJSServerCodegen.java
+++ b/modules/openapi-generator/src/main/java/org/openapitools/codegen/languages/NodeJSServerCodegen.java
@@ -358,7 +358,7 @@ public class NodeJSServerCodegen extends DefaultCodegen implements CodegenConfig

    @Override
    public void preprocessOpenAPI(OpenAPI openAPI) {
-        URL url = URLPathUtils.getServerURL(openAPI);
+        URL url = URLPathUtils.getServerURL(openAPI, serverVariableOverrides());
        String host =  URLPathUtils.getProtocolAndHost(url);
        String port = URLPathUtils.getPort(url, defaultServerPort) ;
        String basePath = url.getPath();
--- a/modules/openapi-generator/src/main/java/org/openapitools/codegen/languages/RustServerCodegen.java
+++ b/modules/openapi-generator/src/main/java/org/openapitools/codegen/languages/RustServerCodegen.java
@@ -24,9 +24,7 @@ import io.swagger.v3.oas.models.info.Info;
 import io.swagger.v3.oas.models.media.ArraySchema;
 import io.swagger.v3.oas.models.media.FileSchema;
 import io.swagger.v3.oas.models.media.Schema;
-import io.swagger.v3.oas.models.media.StringSchema;
 import io.swagger.v3.oas.models.media.XML;
-import io.swagger.v3.oas.models.parameters.Parameter;
 import io.swagger.v3.oas.models.parameters.RequestBody;
 import io.swagger.v3.oas.models.servers.Server;
 import org.apache.commons.lang3.StringUtils;
@@ -291,7 +289,7 @@ public class RustServerCodegen extends DefaultCodegen implements CodegenConfig {
        }
        info.setVersion(StringUtils.join(versionComponents, "."));

-        URL url = URLPathUtils.getServerURL(openAPI);
+        URL url = URLPathUtils.getServerURL(openAPI, serverVariableOverrides());
        additionalProperties.put("serverHost", url.getHost());
        additionalProperties.put("serverPort", URLPathUtils.getPort(url, 80));
    }
--- a/modules/openapi-generator/src/main/java/org/openapitools/codegen/languages/SpringCodegen.java
+++ b/modules/openapi-generator/src/main/java/org/openapitools/codegen/languages/SpringCodegen.java
@@ -515,8 +515,8 @@ public class SpringCodegen extends AbstractJavaCodegen
            additionalProperties.put(TITLE, this.title);
        }

-        if (!additionalProperties.containsKey(SERVER_PORT)) {
-            URL url = URLPathUtils.getServerURL(openAPI);
+        if(!additionalProperties.containsKey(SERVER_PORT)) {
+            URL url = URLPathUtils.getServerURL(openAPI, serverVariableOverrides());
            this.additionalProperties.put(SERVER_PORT, URLPathUtils.getPort(url, 8080));
        }

--- a/modules/openapi-generator/src/main/java/org/openapitools/codegen/utils/URLPathUtils.java
+++ b/modules/openapi-generator/src/main/java/org/openapitools/codegen/utils/URLPathUtils.java
@@ -17,6 +17,7 @@

 package org.openapitools.codegen.utils;

+import com.google.common.collect.ImmutableMap;
 import io.swagger.v3.oas.models.OpenAPI;
 import io.swagger.v3.oas.models.servers.Server;
 import io.swagger.v3.oas.models.servers.ServerVariable;
@@ -28,9 +29,7 @@ import org.slf4j.LoggerFactory;

 import java.net.MalformedURLException;
 import java.net.URL;
-import java.util.HashSet;
-import java.util.List;
-import java.util.Set;
+import java.util.*;
 import java.util.regex.Matcher;
 import java.util.regex.Pattern;

@@ -40,24 +39,28 @@ public class URLPathUtils {
    public static final String LOCAL_HOST = "http://localhost";
    public static final Pattern VARIABLE_PATTERN = Pattern.compile("\\{([^\\}]+)\\}");

-    public static URL getServerURL(OpenAPI openAPI) {
+    // TODO: This should probably be moved into generator/workflow type rather than a static like this.
+    public static URL getServerURL(OpenAPI openAPI, Map<String, String> userDefinedVariables) {
        final List<Server> servers = openAPI.getServers();
        if (servers == null || servers.isEmpty()) {
            LOGGER.warn("Server information seems not defined in the spec. Default to {}.", LOCAL_HOST);
            return getDefaultUrl();
        }
        // TODO need a way to obtain all server URLs
-        return getServerURL(servers.get(0));
+        return getServerURL(servers.get(0), userDefinedVariables);
    }

-    public static URL getServerURL(final Server server) {
+    public static URL getServerURL(final Server server, final Map<String, String> userDefinedVariables) {
        String url = server.getUrl();
        ServerVariables variables = server.getVariables();
        if (variables == null) {
            variables = new ServerVariables();
        }
+
+        Map<String, String> userVariables = userDefinedVariables == null ? new HashMap<>() : ImmutableMap.copyOf(userDefinedVariables);
+
        if (StringUtils.isNotBlank(url)) {
-            url = extractUrl(server, url, variables);
+            url = extractUrl(server, url, variables, userVariables);
            url = sanitizeUrl(url);

            try {
@@ -69,26 +72,37 @@ public class URLPathUtils {
        return getDefaultUrl();
    }

-    private static String extractUrl(Server server, String url, ServerVariables variables) {
+    private static String extractUrl(Server server, String url, ServerVariables variables, Map<String, String> userVariables) {
        Set<String> replacedVariables = new HashSet<>();
        Matcher matcher = VARIABLE_PATTERN.matcher(url);
        while (matcher.find()) {
            if (!replacedVariables.contains(matcher.group())) {
-                ServerVariable variable = variables.get(matcher.group(1));
+                String variableName = matcher.group(1);
+                ServerVariable variable = variables.get(variableName);
                String replacement;
                if (variable != null) {
-                    if (variable.getDefault() != null) {
-                        replacement = variable.getDefault();
-                    } else if (variable.getEnum() != null && !variable.getEnum().isEmpty()) {
-                        replacement = variable.getEnum().get(0);
-                    } else {
-                        LOGGER.warn("No value found for variable '{}' in server definition '{}', default to empty string.", matcher.group(1), server.getUrl());
-                        replacement = "";
+                    String defaultValue = variable.getDefault();
+                    List<String> enumValues = variable.getEnum() == null ? new ArrayList<>() : variable.getEnum();
+                    if (defaultValue == null && !enumValues.isEmpty()) {
+                       defaultValue = enumValues.get(0);
+                    } else if (defaultValue == null) {
+                        defaultValue = "";
+                    }
+
+                    replacement = userVariables.getOrDefault(variableName, defaultValue);
+
+                    if (!enumValues.isEmpty() && !enumValues.contains(replacement)) {
+                        LOGGER.warn("Variable override of '{}' is not listed in the enum of allowed values ({}).", replacement, StringUtils.join(enumValues, ","));
                    }
                } else {
-                    LOGGER.warn("No variable '{}' found in server definition '{}', default to empty string.", matcher.group(1), server.getUrl());
-                    replacement = "";
+                    replacement = userVariables.getOrDefault(variableName, "");
                }
+
+                if (StringUtils.isEmpty(replacement)) {
+                    replacement = "";
+                    LOGGER.warn("No value found for variable '{}' in server definition '{}' and no user override specified, default to empty string.", variableName, server.getUrl());
+                }
+
                url = url.replace(matcher.group(), replacement);
                replacedVariables.add(matcher.group());
                matcher = VARIABLE_PATTERN.matcher(url);
@@ -98,7 +112,7 @@ public class URLPathUtils {
    }

    public static String getScheme(OpenAPI openAPI, CodegenConfig config) {
-        URL url = getServerURL(openAPI);
+        URL url = getServerURL(openAPI, config.serverVariableOverrides());
        return getScheme(url, config);
    }

@@ -176,11 +190,12 @@ public class URLPathUtils {
     * Return the first complete URL from the OpenAPI specification
     *
     * @param openAPI current OpenAPI specification
+     * @param userDefinedVariables User overrides for server variable templating
     * @return host
     */
-    public static String getHost(OpenAPI openAPI) {
+    public static String getHost(OpenAPI openAPI, final Map<String, String> userDefinedVariables) {
        if (openAPI.getServers() != null && openAPI.getServers().size() > 0) {
-            return sanitizeUrl(getServerURL(openAPI.getServers().get(0)).toString());
+            return sanitizeUrl(getServerURL(openAPI.getServers().get(0), userDefinedVariables).toString());
        }
        return LOCAL_HOST;
    }