Reduce RequestBuilder allocations.

Do not initialize the header array unless it's used. When headers are specified by the methodInfo, initialize the ArrayList using the copy constructor.

Do not initialize the query StringBuilder unless it is used.

checkstyle.xml

@@ -96,7 +96,7 @@
         <module name="EqualsHashCode"/>
         <!--module name="HiddenField"/-->
         <module name="IllegalInstantiation"/>
-        <module name="InnerAssignment"/>
+        <!--module name="InnerAssignment"/-->
         <!--module name="MagicNumber"/-->
         <module name="MissingSwitchDefault"/>
         <module name="RedundantThrows"/>

retrofit/src/main/java/retrofit/RequestBuilder.java

@@ -20,7 +20,6 @@
 import java.util.ArrayList;
 import java.util.List;
 import java.util.Map;
-
 import retrofit.client.Header;
 import retrofit.client.Request;
 import retrofit.converter.Converter;
@@ -31,8 +30,6 @@
 
 final class RequestBuilder implements RequestInterceptor.RequestFacade {
   private final Converter converter;
-  private final List<Header> headers;
-  private final StringBuilder queryParams;
   private final String[] paramNames;
   private final RestMethodInfo.ParamUsage[] paramUsages;
   private final String requestMethod;
@@ -43,8 +40,10 @@ final class RequestBuilder implements RequestInterceptor.RequestFacade {
   private final MultipartTypedOutput multipartBody;
   private TypedOutput body;
 
-  private String relativeUrl;
   private String apiUrl;
+  private String relativeUrl;
+  private StringBuilder queryParams;
+  private List<Header> headers;
 
   RequestBuilder(Converter converter, RestMethodInfo methodInfo) {
     this.converter = converter;
@@ -55,18 +54,15 @@ final class RequestBuilder implements RequestInterceptor.RequestFacade {
     isSynchronous = methodInfo.isSynchronous;
     isObservable = methodInfo.isObservable;
 
-    headers = new ArrayList<Header>();
     if (methodInfo.headers != null) {
-      headers.addAll(methodInfo.headers);
+      headers = new ArrayList<Header>(methodInfo.headers);
     }
 
-    queryParams = new StringBuilder();
-
     relativeUrl = methodInfo.requestUrl;
 
     String requestQuery = methodInfo.requestQuery;
     if (requestQuery != null) {
-      queryParams.append('?').append(requestQuery);
+      queryParams = new StringBuilder().append('?').append(requestQuery);
     }
 
     switch (methodInfo.requestType) {
@@ -98,6 +94,10 @@ void setApiUrl(String apiUrl) {
     if (name == null) {
       throw new IllegalArgumentException("Header name must not be null.");
     }
+    List<Header> headers = this.headers;
+    if (headers == null) {
+      this.headers = headers = new ArrayList<Header>(2);
+    }
     headers.add(new Header(name, value));
   }
 
@@ -154,6 +154,10 @@ void addQueryParam(String name, String value, boolean urlEncodeValue) {
         value = URLEncoder.encode(String.valueOf(value), "UTF-8");
       }
       StringBuilder queryParams = this.queryParams;
+      if (queryParams == null) {
+        this.queryParams = queryParams = new StringBuilder();
+      }
+
       queryParams.append(queryParams.length() > 0 ? '&' : '?');
       queryParams.append(name).append('=').append(value);
     } catch (UnsupportedEncodingException e) {
@@ -287,8 +291,11 @@ void setArguments(Object[] args) {
   }
 
   Request build() throws UnsupportedEncodingException {
-    String apiUrl = this.apiUrl;
+    if (multipartBody != null && multipartBody.getPartCount() == 0) {
+      throw new IllegalStateException("Multipart requests must contain at least one part.");
+    }
 
+    String apiUrl = this.apiUrl;
     StringBuilder url = new StringBuilder(apiUrl);
     if (apiUrl.endsWith("/")) {
       // We require relative paths to start with '/'. Prevent a double-slash.
@@ -298,14 +305,10 @@ Request build() throws UnsupportedEncodingException {
     url.append(relativeUrl);
 
     StringBuilder queryParams = this.queryParams;
-    if (queryParams.length() > 0) {
+    if (queryParams != null) {
       url.append(queryParams);
     }
 
-    if (multipartBody != null && multipartBody.getPartCount() == 0) {
-      throw new IllegalStateException("Multipart requests must contain at least one part.");
-    }
-
     return new Request(requestMethod, url.toString(), headers, body);
   }
 }