diff --git a/modules/openapi-generator-cli/src/main/java/org/openapitools/codegen/cmd/ConfigHelp.java b/modules/openapi-generator-cli/src/main/java/org/openapitools/codegen/cmd/ConfigHelp.java
index de79af407f4e..4e51cc7c76ef 100644
--- a/modules/openapi-generator-cli/src/main/java/org/openapitools/codegen/cmd/ConfigHelp.java
+++ b/modules/openapi-generator-cli/src/main/java/org/openapitools/codegen/cmd/ConfigHelp.java
@@ -28,6 +28,7 @@
 
 import java.io.*;
 import java.nio.charset.StandardCharsets;
+import java.nio.file.Paths;
 
 import static org.apache.commons.lang3.StringUtils.isEmpty;
 import static org.apache.commons.lang3.StringUtils.isNotEmpty;
@@ -65,7 +66,7 @@ public void run() {
             generatePlainTextHelp(sb, config);
 
             if (!isEmpty(outputFile)) {
-                File out = new File(outputFile);
+                File out = Paths.get(outputFile).toFile();
                 //noinspection ResultOfMethodCallIgnored
                 out.mkdirs();
 
diff --git a/modules/openapi-generator/src/main/java/org/openapitools/codegen/AbstractGenerator.java b/modules/openapi-generator/src/main/java/org/openapitools/codegen/AbstractGenerator.java
index 88ee01f77e81..176cc3480a4b 100644
--- a/modules/openapi-generator/src/main/java/org/openapitools/codegen/AbstractGenerator.java
+++ b/modules/openapi-generator/src/main/java/org/openapitools/codegen/AbstractGenerator.java
@@ -27,6 +27,7 @@
 import java.io.OutputStreamWriter;
 import java.io.Reader;
 import java.io.Writer;
+import java.nio.file.Paths;
 import java.util.Scanner;
 import java.util.regex.Pattern;
 
@@ -40,7 +41,9 @@ public abstract class AbstractGenerator {
     @SuppressWarnings("static-method")
     public File writeToFile(String filename, String contents) throws IOException {
         LOGGER.info("writing file " + filename);
-        File output = new File(filename);
+
+        // Use Paths.get here to normalize path (for Windows file separator, space escaping on Linux/Mac, etc)
+        File output = Paths.get(filename).toFile();
 
         if (output.getParent() != null && !new File(output.getParent()).exists()) {
             File parent = new File(output.getParent());
diff --git a/modules/openapi-generator/src/main/java/org/openapitools/codegen/DefaultGenerator.java b/modules/openapi-generator/src/main/java/org/openapitools/codegen/DefaultGenerator.java
index 935d15050da2..649227fdf338 100644
--- a/modules/openapi-generator/src/main/java/org/openapitools/codegen/DefaultGenerator.java
+++ b/modules/openapi-generator/src/main/java/org/openapitools/codegen/DefaultGenerator.java
@@ -800,7 +800,7 @@ public Reader getTemplate(String name) {
     }
 
     protected File writeInputStreamToFile(String filename, InputStream in, String templateFile) throws FileNotFoundException, IOException {
-        File outputFile = new File(filename);
+        File outputFile = java.nio.file.Paths.get(filename).toFile();
         if (in != null) {
             OutputStream out = new FileOutputStream(outputFile, false);
             LOGGER.info("writing file " + outputFile);
diff --git a/modules/openapi-generator/src/main/java/org/openapitools/codegen/languages/AbstractJavaCodegen.java b/modules/openapi-generator/src/main/java/org/openapitools/codegen/languages/AbstractJavaCodegen.java
index 008bc0340420..64dd04c8d94f 100644
--- a/modules/openapi-generator/src/main/java/org/openapitools/codegen/languages/AbstractJavaCodegen.java
+++ b/modules/openapi-generator/src/main/java/org/openapitools/codegen/languages/AbstractJavaCodegen.java
@@ -536,32 +536,32 @@ public String escapeReservedWord(String name) {
 
     @Override
     public String apiFileFolder() {
-        return (outputFolder + "/" + sourceFolder + "/" + apiPackage().replace('.', File.separatorChar)).replace('/', File.separatorChar);
+        return (outputFolder + File.separator + sourceFolder + File.separator + apiPackage().replace('.', File.separatorChar)).replace('/', File.separatorChar);
     }
 
     @Override
     public String apiTestFileFolder() {
-        return (outputFolder + "/" + testFolder + "/" + apiPackage().replace('.', File.separatorChar)).replace('/', File.separatorChar);
+        return (outputFolder + File.separator + testFolder + File.separator + apiPackage().replace('.', File.separatorChar)).replace('/', File.separatorChar);
     }
 
     @Override
     public String modelTestFileFolder() {
-        return (outputFolder + "/" + testFolder + "/" + modelPackage().replace('.', File.separatorChar)).replace('/', File.separatorChar);
+        return (outputFolder + File.separator + testFolder + File.separator + modelPackage().replace('.', File.separatorChar)).replace('/', File.separatorChar);
     }
 
     @Override
     public String modelFileFolder() {
-        return (outputFolder + "/" + sourceFolder + "/" + modelPackage().replace('.', File.separatorChar)).replace('/', File.separatorChar);
+        return (outputFolder + File.separator + sourceFolder + File.separator + modelPackage().replace('.', File.separatorChar)).replace('/', File.separatorChar);
     }
 
     @Override
     public String apiDocFileFolder() {
-        return (outputFolder + "/" + apiDocPath).replace('/', File.separatorChar);
+        return (outputFolder + File.separator + apiDocPath).replace('/', File.separatorChar);
     }
 
     @Override
     public String modelDocFileFolder() {
-        return (outputFolder + "/" + modelDocPath).replace('/', File.separatorChar);
+        return (outputFolder + File.separator + modelDocPath).replace('/', File.separatorChar);
     }
 
     @Override
diff --git a/modules/openapi-generator/src/main/java/org/openapitools/codegen/languages/AbstractScalaCodegen.java b/modules/openapi-generator/src/main/java/org/openapitools/codegen/languages/AbstractScalaCodegen.java
index 1e5f9e1867b5..19a45238713c 100644
--- a/modules/openapi-generator/src/main/java/org/openapitools/codegen/languages/AbstractScalaCodegen.java
+++ b/modules/openapi-generator/src/main/java/org/openapitools/codegen/languages/AbstractScalaCodegen.java
@@ -174,12 +174,12 @@ public String escape(String text) {
 
     @Override
     public String apiFileFolder() {
-        return outputFolder + "/" + sourceFolder + "/" + apiPackage().replace('.', File.separatorChar);
+        return outputFolder + File.separator + sourceFolder + File.separator + apiPackage().replace('.', File.separatorChar);
     }
 
     @Override
     public String modelFileFolder() {
-        return outputFolder + "/" + sourceFolder + "/" + modelPackage().replace('.', File.separatorChar);
+        return outputFolder + File.separator + sourceFolder + File.separator + modelPackage().replace('.', File.separatorChar);
     }
 
     @Override
diff --git a/modules/openapi-generator/src/main/java/org/openapitools/codegen/languages/AbstractTypeScriptClientCodegen.java b/modules/openapi-generator/src/main/java/org/openapitools/codegen/languages/AbstractTypeScriptClientCodegen.java
index 3e0db4a7c7ca..e6082564364c 100644
--- a/modules/openapi-generator/src/main/java/org/openapitools/codegen/languages/AbstractTypeScriptClientCodegen.java
+++ b/modules/openapi-generator/src/main/java/org/openapitools/codegen/languages/AbstractTypeScriptClientCodegen.java
@@ -153,12 +153,12 @@ public String escapeReservedWord(String name) {
 
     @Override
     public String apiFileFolder() {
-        return outputFolder + "/" + apiPackage().replace('.', File.separatorChar);
+        return outputFolder + File.separator + apiPackage().replace('.', File.separatorChar);
     }
 
     @Override
     public String modelFileFolder() {
-        return outputFolder + "/" + modelPackage().replace('.', File.separatorChar);
+        return outputFolder + File.separator + modelPackage().replace('.', File.separatorChar);
     }
 
     @Override
diff --git a/modules/openapi-generator/src/main/java/org/openapitools/codegen/languages/AdaCodegen.java b/modules/openapi-generator/src/main/java/org/openapitools/codegen/languages/AdaCodegen.java
index 3a0731106f31..0099e7909871 100644
--- a/modules/openapi-generator/src/main/java/org/openapitools/codegen/languages/AdaCodegen.java
+++ b/modules/openapi-generator/src/main/java/org/openapitools/codegen/languages/AdaCodegen.java
@@ -121,11 +121,11 @@ public void execute(Template.Fragment fragment, Writer writer) throws IOExceptio
 
     @Override
     public String apiFileFolder() {
-        return outputFolder + "/" + apiPackage().replace('.', File.separatorChar);
+        return outputFolder + File.separator + apiPackage().replace('.', File.separatorChar);
     }
 
     @Override
     public String modelFileFolder() {
-        return outputFolder + "/model/" + modelPackage().replace('.', File.separatorChar);
+        return outputFolder + File.separator + "model" + File.separator + modelPackage().replace('.', File.separatorChar);
     }
 }
diff --git a/modules/openapi-generator/src/main/java/org/openapitools/codegen/languages/AdaServerCodegen.java b/modules/openapi-generator/src/main/java/org/openapitools/codegen/languages/AdaServerCodegen.java
index 1e2730951813..0ee5bb6c43e1 100644
--- a/modules/openapi-generator/src/main/java/org/openapitools/codegen/languages/AdaServerCodegen.java
+++ b/modules/openapi-generator/src/main/java/org/openapitools/codegen/languages/AdaServerCodegen.java
@@ -123,11 +123,11 @@ public void execute(Template.Fragment fragment, Writer writer) throws IOExceptio
 
     @Override
     public String apiFileFolder() {
-        return outputFolder + "/" + apiPackage().replace('.', File.separatorChar);
+        return outputFolder + File.separator + apiPackage().replace('.', File.separatorChar);
     }
 
     @Override
     public String modelFileFolder() {
-        return outputFolder + "/model/" + modelPackage().replace('.', File.separatorChar);
+        return outputFolder + File.separator + "model" + File.separator + modelPackage().replace('.', File.separatorChar);
     }
 }
diff --git a/modules/openapi-generator/src/main/java/org/openapitools/codegen/languages/AndroidClientCodegen.java b/modules/openapi-generator/src/main/java/org/openapitools/codegen/languages/AndroidClientCodegen.java
index 73e359075d7c..88640f7de77c 100644
--- a/modules/openapi-generator/src/main/java/org/openapitools/codegen/languages/AndroidClientCodegen.java
+++ b/modules/openapi-generator/src/main/java/org/openapitools/codegen/languages/AndroidClientCodegen.java
@@ -156,22 +156,22 @@ public String escapeReservedWord(String name) {
 
     @Override
     public String apiFileFolder() {
-        return outputFolder + "/" + sourceFolder + "/" + apiPackage().replace('.', File.separatorChar);
+        return outputFolder + File.separator + sourceFolder + File.separator + apiPackage().replace('.', File.separatorChar);
     }
 
     @Override
     public String modelFileFolder() {
-        return outputFolder + "/" + sourceFolder + "/" + modelPackage().replace('.', File.separatorChar);
+        return outputFolder + File.separator + sourceFolder + File.separator + modelPackage().replace('.', File.separatorChar);
     }
 
     @Override
     public String apiDocFileFolder() {
-        return (outputFolder + "/" + apiDocPath).replace('/', File.separatorChar);
+        return outputFolder + File.separator + apiDocPath.replace('/', File.separatorChar);
     }
 
     @Override
     public String modelDocFileFolder() {
-        return (outputFolder + "/" + modelDocPath).replace('/', File.separatorChar);
+        return outputFolder + File.separator + modelDocPath.replace('/', File.separatorChar);
     }
 
     @Override
diff --git a/modules/openapi-generator/src/main/java/org/openapitools/codegen/languages/CSharpDotNet2ClientCodegen.java b/modules/openapi-generator/src/main/java/org/openapitools/codegen/languages/CSharpDotNet2ClientCodegen.java
index 3995cb209960..54f43579dd98 100644
--- a/modules/openapi-generator/src/main/java/org/openapitools/codegen/languages/CSharpDotNet2ClientCodegen.java
+++ b/modules/openapi-generator/src/main/java/org/openapitools/codegen/languages/CSharpDotNet2ClientCodegen.java
@@ -130,12 +130,12 @@ public String modelFileFolder() {
 
     @Override
     public String apiDocFileFolder() {
-        return (outputFolder + "/" + apiDocPath).replace('/', File.separatorChar);
+        return outputFolder + File.separator + apiDocPath.replace('/', File.separatorChar);
     }
 
     @Override
     public String modelDocFileFolder() {
-        return (outputFolder + "/" + modelDocPath).replace('/', File.separatorChar);
+        return outputFolder + File.separator + modelDocPath.replace('/', File.separatorChar);
     }
 
 }
diff --git a/modules/openapi-generator/src/main/java/org/openapitools/codegen/languages/DartClientCodegen.java b/modules/openapi-generator/src/main/java/org/openapitools/codegen/languages/DartClientCodegen.java
index 4ef3879a000a..cf488829506d 100644
--- a/modules/openapi-generator/src/main/java/org/openapitools/codegen/languages/DartClientCodegen.java
+++ b/modules/openapi-generator/src/main/java/org/openapitools/codegen/languages/DartClientCodegen.java
@@ -246,12 +246,12 @@ public String modelFileFolder() {
 
     @Override
     public String apiDocFileFolder() {
-        return (outputFolder + "/" + apiDocPath).replace('/', File.separatorChar);
+        return outputFolder + File.separator + apiDocPath.replace('/', File.separatorChar);
     }
 
     @Override
     public String modelDocFileFolder() {
-        return (outputFolder + "/" + modelDocPath).replace('/', File.separatorChar);
+        return outputFolder + File.separator + modelDocPath.replace('/', File.separatorChar);
     }
 
     @Override
diff --git a/modules/openapi-generator/src/main/java/org/openapitools/codegen/languages/ElmClientCodegen.java b/modules/openapi-generator/src/main/java/org/openapitools/codegen/languages/ElmClientCodegen.java
index 13e811fa1bef..51467c8f8e10 100644
--- a/modules/openapi-generator/src/main/java/org/openapitools/codegen/languages/ElmClientCodegen.java
+++ b/modules/openapi-generator/src/main/java/org/openapitools/codegen/languages/ElmClientCodegen.java
@@ -314,12 +314,12 @@ public String escapeReservedWord(String name) {
 
     @Override
     public String apiFileFolder() {
-        return outputFolder + "/src/Request/" + apiPackage().replace('.', File.separatorChar);
+        return outputFolder + ("/src/Request/" + apiPackage().replace('.', File.separatorChar)).replace("/", File.separator);
     }
 
     @Override
     public String modelFileFolder() {
-        return outputFolder + "/src/Data/" + modelPackage().replace('.', File.separatorChar);
+        return outputFolder + ("/src/Data/" + modelPackage().replace('.', File.separatorChar)).replace("/", File.separator);
     }
 
     @Override
diff --git a/modules/openapi-generator/src/main/java/org/openapitools/codegen/languages/FlashClientCodegen.java b/modules/openapi-generator/src/main/java/org/openapitools/codegen/languages/FlashClientCodegen.java
index a91571f77cf1..750353accefd 100644
--- a/modules/openapi-generator/src/main/java/org/openapitools/codegen/languages/FlashClientCodegen.java
+++ b/modules/openapi-generator/src/main/java/org/openapitools/codegen/languages/FlashClientCodegen.java
@@ -131,7 +131,7 @@ public void processOpts() {
         //modelPackage = invokerPackage + File.separatorChar + "client" + File.separatorChar + "model";
         //apiPackage = invokerPackage + File.separatorChar + "client" + File.separatorChar + "api";
 
-        final String invokerFolder = (sourceFolder + File.separator + "src/" + invokerPackage + File.separator).replace(".", File.separator).replace('.', File.separatorChar);
+        final String invokerFolder = (sourceFolder + File.separator + "src" + File.separator + invokerPackage + File.separator).replace(".", File.separator).replace('.', File.separatorChar);
 
         supportingFiles.add(new SupportingFile("ApiInvoker.as", invokerFolder + "common", "ApiInvoker.as"));
         supportingFiles.add(new SupportingFile("ApiUrlHelper.as", invokerFolder + "common", "ApiUrlHelper.as"));
@@ -193,13 +193,13 @@ public String escapeReservedWord(String name) {
 
     @Override
     public String apiFileFolder() {
-        return (outputFolder + File.separatorChar + sourceFolder + File.separatorChar + "src/"
+        return outputFolder + File.separatorChar + sourceFolder + File.separatorChar + ("src/"
                 + apiPackage().replace('.', File.separatorChar)).replace('/', File.separatorChar);
     }
 
     @Override
     public String modelFileFolder() {
-        return (outputFolder + File.separatorChar + sourceFolder + File.separatorChar + "src/"
+        return outputFolder + File.separatorChar + sourceFolder + File.separatorChar + ("src/"
                 + modelPackage().replace('.', File.separatorChar)).replace('/', File.separatorChar);
     }
 
diff --git a/modules/openapi-generator/src/main/java/org/openapitools/codegen/languages/JMeterClientCodegen.java b/modules/openapi-generator/src/main/java/org/openapitools/codegen/languages/JMeterClientCodegen.java
index 912ad43a7e4c..fdb2a1979712 100644
--- a/modules/openapi-generator/src/main/java/org/openapitools/codegen/languages/JMeterClientCodegen.java
+++ b/modules/openapi-generator/src/main/java/org/openapitools/codegen/languages/JMeterClientCodegen.java
@@ -149,7 +149,7 @@ public String escapeReservedWord(String name) {
      */
     @Override
     public String modelFileFolder() {
-        return outputFolder + "/" + sourceFolder + "/" + modelPackage().replace('.', File.separatorChar);
+        return outputFolder + File.separator + sourceFolder + File.separator + modelPackage().replace('.', File.separatorChar);
     }
 
     /**
@@ -158,7 +158,7 @@ public String modelFileFolder() {
      */
     @Override
     public String apiFileFolder() {
-        return outputFolder + "/" + sourceFolder + "/" + apiPackage().replace('.', File.separatorChar);
+        return outputFolder + File.separator + sourceFolder + File.separator + apiPackage().replace('.', File.separatorChar);
     }
 
     /**
diff --git a/modules/openapi-generator/src/main/java/org/openapitools/codegen/languages/JavascriptClosureAngularClientCodegen.java b/modules/openapi-generator/src/main/java/org/openapitools/codegen/languages/JavascriptClosureAngularClientCodegen.java
index 250e2ed344f8..efab56fc8d6d 100644
--- a/modules/openapi-generator/src/main/java/org/openapitools/codegen/languages/JavascriptClosureAngularClientCodegen.java
+++ b/modules/openapi-generator/src/main/java/org/openapitools/codegen/languages/JavascriptClosureAngularClientCodegen.java
@@ -167,11 +167,11 @@ public String escapeReservedWord(String name) {
 
     @Override
     public String apiFileFolder() {
-        return outputFolder + "/" + apiPackage().replace('.', File.separatorChar);
+        return outputFolder + File.separator + apiPackage().replace('.', File.separatorChar);
     }
 
     public String modelFileFolder() {
-        return outputFolder + "/" + modelPackage().replace('.', File.separatorChar);
+        return outputFolder + File.separator + modelPackage().replace('.', File.separatorChar);
     }
 
     @Override
diff --git a/modules/openapi-generator/src/main/java/org/openapitools/codegen/languages/ScalaGatlingCodegen.java b/modules/openapi-generator/src/main/java/org/openapitools/codegen/languages/ScalaGatlingCodegen.java
index bf7b0beccf94..765b291e37f1 100644
--- a/modules/openapi-generator/src/main/java/org/openapitools/codegen/languages/ScalaGatlingCodegen.java
+++ b/modules/openapi-generator/src/main/java/org/openapitools/codegen/languages/ScalaGatlingCodegen.java
@@ -214,7 +214,7 @@ public String escapeReservedWord(String name) {
      * instantiated
      */
     public String modelFileFolder() {
-        return outputFolder + "/" + sourceFolder + "/" + modelPackage().replace('.', File.separatorChar);
+        return outputFolder + File.separator + sourceFolder + File.separator + modelPackage().replace('.', File.separatorChar);
     }
 
     /**
@@ -223,7 +223,7 @@ public String modelFileFolder() {
      */
     @Override
     public String apiFileFolder() {
-        return outputFolder + "/" + sourceFolder + "/" + apiPackage().replace('.', File.separatorChar);
+        return outputFolder + File.separator + sourceFolder + File.separator + apiPackage().replace('.', File.separatorChar);
     }
 
     /**