Introduced a factory for codegen data containers

This enables users to extend the Codegen* classes
and add their own methods there (which then can
be accessed from the mustache templates)

src/main/java/com/wordnik/swagger/codegen/CodegenModelFactory.java

@@ -0,0 +1,37 @@
+package com.wordnik.swagger.codegen;
+
+import java.util.HashMap;
+import java.util.Map;
+
+public final class CodegenModelFactory {
+
+  private static final Map<CodegenModelType, Class<?>> typeMapping = new HashMap<CodegenModelType, Class<?>>();
+
+  /**
+   * Configure a different implementation class.
+   * @param type the type that shall be replaced
+   * @param implementation the implementation class must extend the default class and must provide a public no-arg constructor
+   */
+  public static void setTypeMapping(CodegenModelType type, Class<?> implementation) {
+    if (!type.getDefaultImplementation().isAssignableFrom(implementation)) {
+      throw new IllegalArgumentException(implementation.getSimpleName() + " doesn't extend " + type.getDefaultImplementation().getSimpleName());
+    }
+    try {
+      implementation.newInstance();
+    } catch (Exception e) {
+      throw new IllegalArgumentException(e);
+    }
+    typeMapping.put(type, implementation);
+  }
+
+  public static <T> T newInstance(CodegenModelType type) {
+    @SuppressWarnings("unchecked") Class<T> classType = (Class<T>) typeMapping.get(type);
+    try {
+      return classType.newInstance();
+    } catch (InstantiationException e) {
+      throw new RuntimeException(e);
+    } catch (IllegalAccessException e) {
+      throw new RuntimeException(e);
+    }
+  }
+}

src/main/java/com/wordnik/swagger/codegen/CodegenModelType.java

@@ -0,0 +1,17 @@
+package com.wordnik.swagger.codegen;
+
+public enum CodegenModelType {
+
+  PARAMETER(CodegenParameter.class),
+  OPERATION(CodegenOperation.class);
+
+  private final Class<?> defaultImplementation;
+
+  private CodegenModelType(Class<?> defaultImplementation) {
+    this.defaultImplementation = defaultImplementation;
+  }
+
+  public Class<?> getDefaultImplementation() {
+    return defaultImplementation;
+  }
+}

src/main/java/com/wordnik/swagger/codegen/DefaultCodegen.java

@@ -1,13 +1,12 @@
 package com.wordnik.swagger.codegen;
 
-import com.wordnik.swagger.util.Json;
 import com.wordnik.swagger.models.*;
 import com.wordnik.swagger.models.parameters.*;
 import com.wordnik.swagger.models.properties.*;
+import com.wordnik.swagger.util.Json;
 import org.apache.commons.lang.StringUtils;
 
 import java.util.*;
-import java.io.File;
 
 public class DefaultCodegen {
   protected String outputFolder = "";
@@ -513,7 +512,7 @@ public class DefaultCodegen {
   }
 
   public CodegenOperation fromOperation(String path, String httpMethod, Operation operation){
-    CodegenOperation op = new CodegenOperation();
+    CodegenOperation op = CodegenModelFactory.newInstance(CodegenModelType.OPERATION);
     Set<String> imports = new HashSet<String>();
 
     String operationId = operation.getOperationId();
@@ -656,7 +655,7 @@ public class DefaultCodegen {
 
     if(parameters != null) {
       for(Parameter param : parameters) {
-        CodegenParameter p = new CodegenParameter();
+        CodegenParameter p = CodegenModelFactory.newInstance(CodegenModelType.PARAMETER);
         p.baseName = param.getName();
         p.description = param.getDescription();
         p.required = param.getRequired();