diff --git a/modules/openapi-generator/src/main/resources/Java/libraries/resttemplate/api.mustache b/modules/openapi-generator/src/main/resources/Java/libraries/resttemplate/api.mustache
index dc6d434c3e43..2f1ed68e9963 100644
--- a/modules/openapi-generator/src/main/resources/Java/libraries/resttemplate/api.mustache
+++ b/modules/openapi-generator/src/main/resources/Java/libraries/resttemplate/api.mustache
@@ -10,7 +10,8 @@ import java.util.Collections;
 import java.util.HashMap;
 import java.util.List;
 import java.util.Locale;
-import java.util.Map;{{/fullJavaUtil}}
+import java.util.Map;
+import java.util.stream.Collectors;{{/fullJavaUtil}}
 
 import org.springframework.beans.factory.annotation.Autowired;
 import org.springframework.stereotype.Component;
@@ -130,7 +131,7 @@ public class {{classname}} {
         {{/hasMore}}{{/cookieParams}}{{/hasCookieParams}}{{#hasFormParams}}
 
         {{#formParams}}if ({{paramName}} != null)
-            formParams.{{^collectionFormat}}add{{/collectionFormat}}{{#collectionFormat}}put{{/collectionFormat}}("{{baseName}}", {{#isFile}}new FileSystemResource({{paramName}}){{/isFile}}{{^isFile}}{{paramName}}{{/isFile}});{{#hasMore}}
+            formParams.{{^collectionFormat}}add{{/collectionFormat}}{{#collectionFormat}}put{{/collectionFormat}}("{{baseName}}", {{#isFile}}{{^collectionFormat}}new FileSystemResource({{paramName}}){{/collectionFormat}}{{/isFile}}{{#isFile}}{{#collectionFormat}}{{paramName}}.stream().map(FileSystemResource::new).collect(Collectors.toList()){{/collectionFormat}}{{/isFile}}{{^isFile}}{{paramName}}{{/isFile}});{{#hasMore}}
         {{/hasMore}}{{/formParams}}{{/hasFormParams}}
 
         final String[] accepts = { {{#hasProduces}}
diff --git a/modules/openapi-generator/src/main/resources/Java/libraries/webclient/api.mustache b/modules/openapi-generator/src/main/resources/Java/libraries/webclient/api.mustache
index 7b3c23d59b48..a8077006c8ff 100644
--- a/modules/openapi-generator/src/main/resources/Java/libraries/webclient/api.mustache
+++ b/modules/openapi-generator/src/main/resources/Java/libraries/webclient/api.mustache
@@ -10,6 +10,7 @@ import java.util.HashMap;
 import java.util.List;
 import java.util.Locale;
 import java.util.Map;
+import java.util.stream.Collectors;
 {{/fullJavaUtil}}
 
 import org.springframework.beans.factory.annotation.Autowired;
@@ -108,7 +109,7 @@ public class {{classname}} {
 
         {{#formParams}}
         if ({{paramName}} != null)
-            formParams.add{{#collectionFormat}}All{{/collectionFormat}}("{{baseName}}", {{#isFile}}new FileSystemResource({{paramName}}){{/isFile}}{{^isFile}}{{paramName}}{{/isFile}});
+            formParams.add{{#collectionFormat}}All{{/collectionFormat}}("{{baseName}}", {{#isFile}}{{^collectionFormat}}new FileSystemResource({{paramName}}){{/collectionFormat}}{{/isFile}}{{#isFile}}{{#collectionFormat}}{{paramName}}.stream().map(FileSystemResource::new).collect(Collectors.toList()){{/collectionFormat}}{{/isFile}}{{^isFile}}{{paramName}}{{/isFile}});
         {{/formParams}}
         {{/hasFormParams}}
 
diff --git a/modules/openapi-generator/src/test/java/org/openapitools/codegen/java/JavaClientCodegenTest.java b/modules/openapi-generator/src/test/java/org/openapitools/codegen/java/JavaClientCodegenTest.java
index 0a9bae81ed67..6d61c93b3efc 100644
--- a/modules/openapi-generator/src/test/java/org/openapitools/codegen/java/JavaClientCodegenTest.java
+++ b/modules/openapi-generator/src/test/java/org/openapitools/codegen/java/JavaClientCodegenTest.java
@@ -26,10 +26,8 @@
 import io.swagger.v3.oas.models.responses.ApiResponse;
 import io.swagger.v3.parser.util.SchemaTypeUtil;
 import org.openapitools.codegen.*;
-import org.openapitools.codegen.MockDefaultGenerator.WrittenTemplateBasedFile;
 import org.openapitools.codegen.config.CodegenConfigurator;
 import org.openapitools.codegen.languages.AbstractJavaCodegen;
-import org.openapitools.codegen.languages.DartClientCodegen;
 import org.openapitools.codegen.languages.JavaClientCodegen;
 import org.testng.Assert;
 import org.testng.annotations.Test;
@@ -842,4 +840,91 @@ public void testAnyType() {
         Assert.assertFalse(cp9.isFreeFormObject);
         Assert.assertFalse(cp9.isAnyType);
     }
+
+    /**
+     * See https://github.com/OpenAPITools/openapi-generator/issues/4803
+     */
+    @Test
+    public void testRestTemplateFormMultipart() throws IOException {
+
+        Map<String, Object> properties = new HashMap<>();
+        properties.put(JavaClientCodegen.JAVA8_MODE, true);
+        properties.put(CodegenConstants.API_PACKAGE, "xyz.abcdef.api");
+
+
+        File output = Files.createTempDirectory("test").toFile();
+        output.deleteOnExit();
+
+        final CodegenConfigurator configurator = new CodegenConfigurator()
+                .setGeneratorName("java")
+                .setLibrary(JavaClientCodegen.RESTTEMPLATE)
+                .setAdditionalProperties(properties)
+                .setInputSpec("src/test/resources/3_0/form-multipart-binary-array.yaml")
+                .setOutputDir(output.getAbsolutePath().replace("\\", "/"));
+
+
+        DefaultGenerator generator = new DefaultGenerator();
+        List<File> files = generator.opts(configurator.toClientOptInput()).generate();
+        files.forEach(File::deleteOnExit);
+
+
+        Path defaultApi = Paths.get(output + "/src/main/java/xyz/abcdef/api/MultipartApi.java");
+        TestUtils.assertFileContains(defaultApi,
+                //multiple files
+                "multipartArrayWithHttpInfo(List<File> files)",
+                "formParams.put(\"files\", files.stream().map(FileSystemResource::new).collect(Collectors.toList()));",
+
+                //mixed
+                "multipartMixedWithHttpInfo(File file, MultipartMixedMarker marker)",
+                "formParams.add(\"file\", new FileSystemResource(file));",
+
+                //single file
+                "multipartSingleWithHttpInfo(File file)",
+                "formParams.add(\"file\", new FileSystemResource(file));"
+                );
+    }
+
+    /**
+     * See https://github.com/OpenAPITools/openapi-generator/issues/4803
+     */
+    @Test
+    public void testWebClientFormMultipart() throws IOException {
+
+        Map<String, Object> properties = new HashMap<>();
+        properties.put(JavaClientCodegen.JAVA8_MODE, true);
+        properties.put(CodegenConstants.API_PACKAGE, "xyz.abcdef.api");
+
+
+        File output = Files.createTempDirectory("test").toFile();
+        output.deleteOnExit();
+
+        final CodegenConfigurator configurator = new CodegenConfigurator()
+                .setGeneratorName("java")
+                .setLibrary(JavaClientCodegen.WEBCLIENT)
+                .setAdditionalProperties(properties)
+                .setInputSpec("src/test/resources/3_0/form-multipart-binary-array.yaml")
+                .setOutputDir(output.getAbsolutePath().replace("\\", "/"));
+
+
+        DefaultGenerator generator = new DefaultGenerator();
+        List<File> files = generator.opts(configurator.toClientOptInput()).generate();
+        files.forEach(File::deleteOnExit);
+
+
+        Path defaultApi = Paths.get(output + "/src/main/java/xyz/abcdef/api/MultipartApi.java");
+        TestUtils.assertFileContains(defaultApi,
+                //multiple files
+                "multipartArray(List<File> files)",
+                "formParams.addAll(\"files\", files.stream().map(FileSystemResource::new).collect(Collectors.toList()));",
+
+                //mixed
+                "multipartMixed(File file, MultipartMixedMarker marker)",
+                "formParams.add(\"file\", new FileSystemResource(file));",
+
+                //single file
+                "multipartSingle(File file)",
+                "formParams.add(\"file\", new FileSystemResource(file));"
+        );
+    }
+
 }
diff --git a/samples/client/petstore/java/resttemplate-withXml/src/main/java/org/openapitools/client/api/AnotherFakeApi.java b/samples/client/petstore/java/resttemplate-withXml/src/main/java/org/openapitools/client/api/AnotherFakeApi.java
index 125dfe43c2af..0e9eaf39cd4b 100644
--- a/samples/client/petstore/java/resttemplate-withXml/src/main/java/org/openapitools/client/api/AnotherFakeApi.java
+++ b/samples/client/petstore/java/resttemplate-withXml/src/main/java/org/openapitools/client/api/AnotherFakeApi.java
@@ -10,6 +10,7 @@
 import java.util.List;
 import java.util.Locale;
 import java.util.Map;
+import java.util.stream.Collectors;
 
 import org.springframework.beans.factory.annotation.Autowired;
 import org.springframework.stereotype.Component;
diff --git a/samples/client/petstore/java/resttemplate-withXml/src/main/java/org/openapitools/client/api/FakeApi.java b/samples/client/petstore/java/resttemplate-withXml/src/main/java/org/openapitools/client/api/FakeApi.java
index 4fe805f179d9..e3fda6c1ee12 100644
--- a/samples/client/petstore/java/resttemplate-withXml/src/main/java/org/openapitools/client/api/FakeApi.java
+++ b/samples/client/petstore/java/resttemplate-withXml/src/main/java/org/openapitools/client/api/FakeApi.java
@@ -18,6 +18,7 @@
 import java.util.List;
 import java.util.Locale;
 import java.util.Map;
+import java.util.stream.Collectors;
 
 import org.springframework.beans.factory.annotation.Autowired;
 import org.springframework.stereotype.Component;
diff --git a/samples/client/petstore/java/resttemplate-withXml/src/main/java/org/openapitools/client/api/FakeClassnameTags123Api.java b/samples/client/petstore/java/resttemplate-withXml/src/main/java/org/openapitools/client/api/FakeClassnameTags123Api.java
index e8363fe361b2..d9c821519609 100644
--- a/samples/client/petstore/java/resttemplate-withXml/src/main/java/org/openapitools/client/api/FakeClassnameTags123Api.java
+++ b/samples/client/petstore/java/resttemplate-withXml/src/main/java/org/openapitools/client/api/FakeClassnameTags123Api.java
@@ -10,6 +10,7 @@
 import java.util.List;
 import java.util.Locale;
 import java.util.Map;
+import java.util.stream.Collectors;
 
 import org.springframework.beans.factory.annotation.Autowired;
 import org.springframework.stereotype.Component;
diff --git a/samples/client/petstore/java/resttemplate-withXml/src/main/java/org/openapitools/client/api/PetApi.java b/samples/client/petstore/java/resttemplate-withXml/src/main/java/org/openapitools/client/api/PetApi.java
index 896f7773eeb2..eac8abdc3ccd 100644
--- a/samples/client/petstore/java/resttemplate-withXml/src/main/java/org/openapitools/client/api/PetApi.java
+++ b/samples/client/petstore/java/resttemplate-withXml/src/main/java/org/openapitools/client/api/PetApi.java
@@ -13,6 +13,7 @@
 import java.util.List;
 import java.util.Locale;
 import java.util.Map;
+import java.util.stream.Collectors;
 
 import org.springframework.beans.factory.annotation.Autowired;
 import org.springframework.stereotype.Component;
diff --git a/samples/client/petstore/java/resttemplate-withXml/src/main/java/org/openapitools/client/api/StoreApi.java b/samples/client/petstore/java/resttemplate-withXml/src/main/java/org/openapitools/client/api/StoreApi.java
index b4041f3291e0..d2897deda183 100644
--- a/samples/client/petstore/java/resttemplate-withXml/src/main/java/org/openapitools/client/api/StoreApi.java
+++ b/samples/client/petstore/java/resttemplate-withXml/src/main/java/org/openapitools/client/api/StoreApi.java
@@ -10,6 +10,7 @@
 import java.util.List;
 import java.util.Locale;
 import java.util.Map;
+import java.util.stream.Collectors;
 
 import org.springframework.beans.factory.annotation.Autowired;
 import org.springframework.stereotype.Component;
diff --git a/samples/client/petstore/java/resttemplate-withXml/src/main/java/org/openapitools/client/api/UserApi.java b/samples/client/petstore/java/resttemplate-withXml/src/main/java/org/openapitools/client/api/UserApi.java
index 996273ebf09d..7dea94d09185 100644
--- a/samples/client/petstore/java/resttemplate-withXml/src/main/java/org/openapitools/client/api/UserApi.java
+++ b/samples/client/petstore/java/resttemplate-withXml/src/main/java/org/openapitools/client/api/UserApi.java
@@ -10,6 +10,7 @@
 import java.util.List;
 import java.util.Locale;
 import java.util.Map;
+import java.util.stream.Collectors;
 
 import org.springframework.beans.factory.annotation.Autowired;
 import org.springframework.stereotype.Component;
diff --git a/samples/client/petstore/java/resttemplate/src/main/java/org/openapitools/client/api/AnotherFakeApi.java b/samples/client/petstore/java/resttemplate/src/main/java/org/openapitools/client/api/AnotherFakeApi.java
index 125dfe43c2af..0e9eaf39cd4b 100644
--- a/samples/client/petstore/java/resttemplate/src/main/java/org/openapitools/client/api/AnotherFakeApi.java
+++ b/samples/client/petstore/java/resttemplate/src/main/java/org/openapitools/client/api/AnotherFakeApi.java
@@ -10,6 +10,7 @@
 import java.util.List;
 import java.util.Locale;
 import java.util.Map;
+import java.util.stream.Collectors;
 
 import org.springframework.beans.factory.annotation.Autowired;
 import org.springframework.stereotype.Component;
diff --git a/samples/client/petstore/java/resttemplate/src/main/java/org/openapitools/client/api/FakeApi.java b/samples/client/petstore/java/resttemplate/src/main/java/org/openapitools/client/api/FakeApi.java
index 4fe805f179d9..e3fda6c1ee12 100644
--- a/samples/client/petstore/java/resttemplate/src/main/java/org/openapitools/client/api/FakeApi.java
+++ b/samples/client/petstore/java/resttemplate/src/main/java/org/openapitools/client/api/FakeApi.java
@@ -18,6 +18,7 @@
 import java.util.List;
 import java.util.Locale;
 import java.util.Map;
+import java.util.stream.Collectors;
 
 import org.springframework.beans.factory.annotation.Autowired;
 import org.springframework.stereotype.Component;
diff --git a/samples/client/petstore/java/resttemplate/src/main/java/org/openapitools/client/api/FakeClassnameTags123Api.java b/samples/client/petstore/java/resttemplate/src/main/java/org/openapitools/client/api/FakeClassnameTags123Api.java
index e8363fe361b2..d9c821519609 100644
--- a/samples/client/petstore/java/resttemplate/src/main/java/org/openapitools/client/api/FakeClassnameTags123Api.java
+++ b/samples/client/petstore/java/resttemplate/src/main/java/org/openapitools/client/api/FakeClassnameTags123Api.java
@@ -10,6 +10,7 @@
 import java.util.List;
 import java.util.Locale;
 import java.util.Map;
+import java.util.stream.Collectors;
 
 import org.springframework.beans.factory.annotation.Autowired;
 import org.springframework.stereotype.Component;
diff --git a/samples/client/petstore/java/resttemplate/src/main/java/org/openapitools/client/api/PetApi.java b/samples/client/petstore/java/resttemplate/src/main/java/org/openapitools/client/api/PetApi.java
index 896f7773eeb2..eac8abdc3ccd 100644
--- a/samples/client/petstore/java/resttemplate/src/main/java/org/openapitools/client/api/PetApi.java
+++ b/samples/client/petstore/java/resttemplate/src/main/java/org/openapitools/client/api/PetApi.java
@@ -13,6 +13,7 @@
 import java.util.List;
 import java.util.Locale;
 import java.util.Map;
+import java.util.stream.Collectors;
 
 import org.springframework.beans.factory.annotation.Autowired;
 import org.springframework.stereotype.Component;
diff --git a/samples/client/petstore/java/resttemplate/src/main/java/org/openapitools/client/api/StoreApi.java b/samples/client/petstore/java/resttemplate/src/main/java/org/openapitools/client/api/StoreApi.java
index b4041f3291e0..d2897deda183 100644
--- a/samples/client/petstore/java/resttemplate/src/main/java/org/openapitools/client/api/StoreApi.java
+++ b/samples/client/petstore/java/resttemplate/src/main/java/org/openapitools/client/api/StoreApi.java
@@ -10,6 +10,7 @@
 import java.util.List;
 import java.util.Locale;
 import java.util.Map;
+import java.util.stream.Collectors;
 
 import org.springframework.beans.factory.annotation.Autowired;
 import org.springframework.stereotype.Component;
diff --git a/samples/client/petstore/java/resttemplate/src/main/java/org/openapitools/client/api/UserApi.java b/samples/client/petstore/java/resttemplate/src/main/java/org/openapitools/client/api/UserApi.java
index 996273ebf09d..7dea94d09185 100644
--- a/samples/client/petstore/java/resttemplate/src/main/java/org/openapitools/client/api/UserApi.java
+++ b/samples/client/petstore/java/resttemplate/src/main/java/org/openapitools/client/api/UserApi.java
@@ -10,6 +10,7 @@
 import java.util.List;
 import java.util.Locale;
 import java.util.Map;
+import java.util.stream.Collectors;
 
 import org.springframework.beans.factory.annotation.Autowired;
 import org.springframework.stereotype.Component;
diff --git a/samples/client/petstore/java/webclient/src/main/java/org/openapitools/client/api/AnotherFakeApi.java b/samples/client/petstore/java/webclient/src/main/java/org/openapitools/client/api/AnotherFakeApi.java
index a0401a7fed37..edc44d999374 100644
--- a/samples/client/petstore/java/webclient/src/main/java/org/openapitools/client/api/AnotherFakeApi.java
+++ b/samples/client/petstore/java/webclient/src/main/java/org/openapitools/client/api/AnotherFakeApi.java
@@ -8,6 +8,7 @@
 import java.util.List;
 import java.util.Locale;
 import java.util.Map;
+import java.util.stream.Collectors;
 
 import org.springframework.beans.factory.annotation.Autowired;
 import org.springframework.util.LinkedMultiValueMap;
diff --git a/samples/client/petstore/java/webclient/src/main/java/org/openapitools/client/api/FakeApi.java b/samples/client/petstore/java/webclient/src/main/java/org/openapitools/client/api/FakeApi.java
index 4e16c1bbd672..95108f72e5e1 100644
--- a/samples/client/petstore/java/webclient/src/main/java/org/openapitools/client/api/FakeApi.java
+++ b/samples/client/petstore/java/webclient/src/main/java/org/openapitools/client/api/FakeApi.java
@@ -16,6 +16,7 @@
 import java.util.List;
 import java.util.Locale;
 import java.util.Map;
+import java.util.stream.Collectors;
 
 import org.springframework.beans.factory.annotation.Autowired;
 import org.springframework.util.LinkedMultiValueMap;
diff --git a/samples/client/petstore/java/webclient/src/main/java/org/openapitools/client/api/FakeClassnameTags123Api.java b/samples/client/petstore/java/webclient/src/main/java/org/openapitools/client/api/FakeClassnameTags123Api.java
index eb9dca43bfd0..2a2d3f3e1d8d 100644
--- a/samples/client/petstore/java/webclient/src/main/java/org/openapitools/client/api/FakeClassnameTags123Api.java
+++ b/samples/client/petstore/java/webclient/src/main/java/org/openapitools/client/api/FakeClassnameTags123Api.java
@@ -8,6 +8,7 @@
 import java.util.List;
 import java.util.Locale;
 import java.util.Map;
+import java.util.stream.Collectors;
 
 import org.springframework.beans.factory.annotation.Autowired;
 import org.springframework.util.LinkedMultiValueMap;
diff --git a/samples/client/petstore/java/webclient/src/main/java/org/openapitools/client/api/PetApi.java b/samples/client/petstore/java/webclient/src/main/java/org/openapitools/client/api/PetApi.java
index eeac635d156e..3749fe40927c 100644
--- a/samples/client/petstore/java/webclient/src/main/java/org/openapitools/client/api/PetApi.java
+++ b/samples/client/petstore/java/webclient/src/main/java/org/openapitools/client/api/PetApi.java
@@ -11,6 +11,7 @@
 import java.util.List;
 import java.util.Locale;
 import java.util.Map;
+import java.util.stream.Collectors;
 
 import org.springframework.beans.factory.annotation.Autowired;
 import org.springframework.util.LinkedMultiValueMap;
diff --git a/samples/client/petstore/java/webclient/src/main/java/org/openapitools/client/api/StoreApi.java b/samples/client/petstore/java/webclient/src/main/java/org/openapitools/client/api/StoreApi.java
index 6fd8ced9ca21..98d603a25455 100644
--- a/samples/client/petstore/java/webclient/src/main/java/org/openapitools/client/api/StoreApi.java
+++ b/samples/client/petstore/java/webclient/src/main/java/org/openapitools/client/api/StoreApi.java
@@ -8,6 +8,7 @@
 import java.util.List;
 import java.util.Locale;
 import java.util.Map;
+import java.util.stream.Collectors;
 
 import org.springframework.beans.factory.annotation.Autowired;
 import org.springframework.util.LinkedMultiValueMap;
diff --git a/samples/client/petstore/java/webclient/src/main/java/org/openapitools/client/api/UserApi.java b/samples/client/petstore/java/webclient/src/main/java/org/openapitools/client/api/UserApi.java
index c5d010170141..62188c93a1cc 100644
--- a/samples/client/petstore/java/webclient/src/main/java/org/openapitools/client/api/UserApi.java
+++ b/samples/client/petstore/java/webclient/src/main/java/org/openapitools/client/api/UserApi.java
@@ -8,6 +8,7 @@
 import java.util.List;
 import java.util.Locale;
 import java.util.Map;
+import java.util.stream.Collectors;
 
 import org.springframework.beans.factory.annotation.Autowired;
 import org.springframework.util.LinkedMultiValueMap;