Fix apache http client query parameters (#14193)

modules/openapi-generator/src/main/resources/Java/libraries/apache-httpclient/api.mustache

@@ -91,7 +91,7 @@ public class {{classname}} {
                 {{#hasVars}}
                     {{#vars}}
                         {{#isArray}}
-    localVarQueryParams.addAll(apiClient.parameterToPair("multi", "{{baseName}}", {{paramName}}.{{getter}}()));
+    localVarQueryParams.addAll(apiClient.parameterToPairs("multi", "{{baseName}}", {{paramName}}.{{getter}}()));
                         {{/isArray}}
                         {{^isArray}}
     localVarQueryParams.addAll(apiClient.parameterToPair("{{baseName}}", {{paramName}}.{{getter}}()));

modules/openapi-generator/src/test/java/org/openapitools/codegen/java/apachehttpclient/ApacheHttpClientCodegenTest.java

@@ -87,7 +87,7 @@ public class ApacheHttpClientCodegenTest {
         generator.opts(clientOptInput).generate();
 
         TestUtils.assertFileContains(Paths.get(output + "/src/main/java/xyz/abcdef/api/DefaultApi.java"),
-            "localVarQueryParams.addAll(apiClient.parameterToPair(\"multi\", \"values\", queryObject.getValues()))"
+            "localVarQueryParams.addAll(apiClient.parameterToPairs(\"multi\", \"values\", queryObject.getValues()))"
         );
     }
 }

samples/client/petstore/rust/reqwest/petstore-async-middleware/src/apis/mod.rs

@@ -70,6 +70,35 @@ pub fn urlencode<T: AsRef<str>>(s: T) -> String {
     ::url::form_urlencoded::byte_serialize(s.as_ref().as_bytes()).collect()
 }
 
+pub fn parse_deep_object(prefix: &str, value: &serde_json::Value) -> Vec<(String, String)> {
+    if let serde_json::Value::Object(object) = value {
+        let mut params = vec![];
+
+        for (key, value) in object {
+            match value {
+                serde_json::Value::Object(_) => params.append(&mut parse_deep_object(
+                    &format!("{}[{}]", prefix, key),
+                    value,
+                )),
+                serde_json::Value::Array(array) => {
+                    for (i, value) in array.iter().enumerate() {
+                        params.append(&mut parse_deep_object(
+                            &format!("{}[{}][{}]", prefix, key, i),
+                            value,
+                        ));
+                    }
+                },
+                serde_json::Value::String(s) => params.push((format!("{}[{}]", prefix, key), s.clone())),
+                _ => params.push((format!("{}[{}]", prefix, key), value.to_string())),
+            }
+        }
+
+        return params;
+    }
+
+    unimplemented!("Only objects are supported with style=deepObject")
+}
+
 pub mod fake_api;
 pub mod pet_api;
 pub mod store_api;