Add alias type definitions for Java

When a spec defines a Model at the top level that is a non-aggretate type (such
as string, number or boolean), it essentially represents an alias for the simple
type. For example, the following spec snippet creates an alias of the boolean
type that for all intents and purposes acts just like a regular boolean.

    definitions:
      JustABoolean:
        type: boolean

This can be modeled in some languages through built-in mechanisms, such as
typedefs in C++. Java, however, just not have a clean way of representing this.

This change introduces an internal mechanism for representing aliases. It
maintains a map in DefaultCodegen that tracks these types of definitions, and
wherever it sees the "JustABoolean" type in the spec, it generates code that
uses the built-in "Boolean" instead.

This functionality currenlty only applies to Java, but could be extended to
other languages later.

The change adds a few examples of this to the fake endpoint spec for testing,
which means all of the samples change as well.

samples/client/petstore/java/jersey2-java8/src/main/java/io/swagger/client/api/FakeApi.java

@@ -11,6 +11,7 @@ import java.math.BigDecimal;
 import io.swagger.client.model.Client;
 import java.time.LocalDate;
 import java.time.OffsetDateTime;
+import io.swagger.client.model.OuterComposite;
 
 import java.util.ArrayList;
 import java.util.HashMap;
@@ -37,6 +38,150 @@ public class FakeApi {
     this.apiClient = apiClient;
   }
 
+  /**
+   * 
+   * Test serialization of outer boolean types
+   * @param body Input boolean as post body (optional)
+   * @return Boolean
+   * @throws ApiException if fails to make API call
+   */
+  public Boolean fakeOuterBooleanSerialize(Boolean body) throws ApiException {
+    Object localVarPostBody = body;
+    
+    // create path and map variables
+    String localVarPath = "/fake/outer/boolean";
+
+    // query params
+    List<Pair> localVarQueryParams = new ArrayList<Pair>();
+    Map<String, String> localVarHeaderParams = new HashMap<String, String>();
+    Map<String, Object> localVarFormParams = new HashMap<String, Object>();
+
+
+    
+    
+    final String[] localVarAccepts = {
+      
+    };
+    final String localVarAccept = apiClient.selectHeaderAccept(localVarAccepts);
+
+    final String[] localVarContentTypes = {
+      
+    };
+    final String localVarContentType = apiClient.selectHeaderContentType(localVarContentTypes);
+
+    String[] localVarAuthNames = new String[] {  };
+
+    GenericType<Boolean> localVarReturnType = new GenericType<Boolean>() {};
+    return apiClient.invokeAPI(localVarPath, "POST", localVarQueryParams, localVarPostBody, localVarHeaderParams, localVarFormParams, localVarAccept, localVarContentType, localVarAuthNames, localVarReturnType);
+      }
+  /**
+   * 
+   * Test serialization of object with outer number type
+   * @param body Input composite as post body (optional)
+   * @return OuterComposite
+   * @throws ApiException if fails to make API call
+   */
+  public OuterComposite fakeOuterCompositeSerialize(OuterComposite body) throws ApiException {
+    Object localVarPostBody = body;
+    
+    // create path and map variables
+    String localVarPath = "/fake/outer/composite";
+
+    // query params
+    List<Pair> localVarQueryParams = new ArrayList<Pair>();
+    Map<String, String> localVarHeaderParams = new HashMap<String, String>();
+    Map<String, Object> localVarFormParams = new HashMap<String, Object>();
+
+
+    
+    
+    final String[] localVarAccepts = {
+      
+    };
+    final String localVarAccept = apiClient.selectHeaderAccept(localVarAccepts);
+
+    final String[] localVarContentTypes = {
+      
+    };
+    final String localVarContentType = apiClient.selectHeaderContentType(localVarContentTypes);
+
+    String[] localVarAuthNames = new String[] {  };
+
+    GenericType<OuterComposite> localVarReturnType = new GenericType<OuterComposite>() {};
+    return apiClient.invokeAPI(localVarPath, "POST", localVarQueryParams, localVarPostBody, localVarHeaderParams, localVarFormParams, localVarAccept, localVarContentType, localVarAuthNames, localVarReturnType);
+      }
+  /**
+   * 
+   * Test serialization of outer number types
+   * @param body Input number as post body (optional)
+   * @return BigDecimal
+   * @throws ApiException if fails to make API call
+   */
+  public BigDecimal fakeOuterNumberSerialize(BigDecimal body) throws ApiException {
+    Object localVarPostBody = body;
+    
+    // create path and map variables
+    String localVarPath = "/fake/outer/number";
+
+    // query params
+    List<Pair> localVarQueryParams = new ArrayList<Pair>();
+    Map<String, String> localVarHeaderParams = new HashMap<String, String>();
+    Map<String, Object> localVarFormParams = new HashMap<String, Object>();
+
+
+    
+    
+    final String[] localVarAccepts = {
+      
+    };
+    final String localVarAccept = apiClient.selectHeaderAccept(localVarAccepts);
+
+    final String[] localVarContentTypes = {
+      
+    };
+    final String localVarContentType = apiClient.selectHeaderContentType(localVarContentTypes);
+
+    String[] localVarAuthNames = new String[] {  };
+
+    GenericType<BigDecimal> localVarReturnType = new GenericType<BigDecimal>() {};
+    return apiClient.invokeAPI(localVarPath, "POST", localVarQueryParams, localVarPostBody, localVarHeaderParams, localVarFormParams, localVarAccept, localVarContentType, localVarAuthNames, localVarReturnType);
+      }
+  /**
+   * 
+   * Test serialization of outer string types
+   * @param body Input string as post body (optional)
+   * @return String
+   * @throws ApiException if fails to make API call
+   */
+  public String fakeOuterStringSerialize(String body) throws ApiException {
+    Object localVarPostBody = body;
+    
+    // create path and map variables
+    String localVarPath = "/fake/outer/string";
+
+    // query params
+    List<Pair> localVarQueryParams = new ArrayList<Pair>();
+    Map<String, String> localVarHeaderParams = new HashMap<String, String>();
+    Map<String, Object> localVarFormParams = new HashMap<String, Object>();
+
+
+    
+    
+    final String[] localVarAccepts = {
+      
+    };
+    final String localVarAccept = apiClient.selectHeaderAccept(localVarAccepts);
+
+    final String[] localVarContentTypes = {
+      
+    };
+    final String localVarContentType = apiClient.selectHeaderContentType(localVarContentTypes);
+
+    String[] localVarAuthNames = new String[] {  };
+
+    GenericType<String> localVarReturnType = new GenericType<String>() {};
+    return apiClient.invokeAPI(localVarPath, "POST", localVarQueryParams, localVarPostBody, localVarHeaderParams, localVarFormParams, localVarAccept, localVarContentType, localVarAuthNames, localVarReturnType);
+      }
   /**
    * To test \&quot;client\&quot; model
    * To test \&quot;client\&quot; model

samples/client/petstore/java/jersey2-java8/src/main/java/io/swagger/client/model/OuterComposite.java

@@ -0,0 +1,136 @@
+/*
+ * Swagger Petstore
+ * This spec is mainly for testing Petstore server and contains fake endpoints, models. Please do not use this for any other purpose. Special characters: \" \\
+ *
+ * OpenAPI spec version: 1.0.0
+ * Contact: apiteam@swagger.io
+ *
+ * NOTE: This class is auto generated by the swagger code generator program.
+ * https://github.com/swagger-api/swagger-codegen.git
+ * Do not edit the class manually.
+ */
+
+
+package io.swagger.client.model;
+
+import java.util.Objects;
+import com.fasterxml.jackson.annotation.JsonProperty;
+import com.fasterxml.jackson.annotation.JsonCreator;
+import io.swagger.annotations.ApiModel;
+import io.swagger.annotations.ApiModelProperty;
+import java.math.BigDecimal;
+
+/**
+ * OuterComposite
+ */
+
+public class OuterComposite {
+  @JsonProperty("my_number")
+  private BigDecimal myNumber = null;
+
+  @JsonProperty("my_string")
+  private String myString = null;
+
+  @JsonProperty("my_boolean")
+  private Boolean myBoolean = null;
+
+  public OuterComposite myNumber(BigDecimal myNumber) {
+    this.myNumber = myNumber;
+    return this;
+  }
+
+   /**
+   * Get myNumber
+   * @return myNumber
+  **/
+  @ApiModelProperty(value = "")
+  public BigDecimal getMyNumber() {
+    return myNumber;
+  }
+
+  public void setMyNumber(BigDecimal myNumber) {
+    this.myNumber = myNumber;
+  }
+
+  public OuterComposite myString(String myString) {
+    this.myString = myString;
+    return this;
+  }
+
+   /**
+   * Get myString
+   * @return myString
+  **/
+  @ApiModelProperty(value = "")
+  public String getMyString() {
+    return myString;
+  }
+
+  public void setMyString(String myString) {
+    this.myString = myString;
+  }
+
+  public OuterComposite myBoolean(Boolean myBoolean) {
+    this.myBoolean = myBoolean;
+    return this;
+  }
+
+   /**
+   * Get myBoolean
+   * @return myBoolean
+  **/
+  @ApiModelProperty(value = "")
+  public Boolean getMyBoolean() {
+    return myBoolean;
+  }
+
+  public void setMyBoolean(Boolean myBoolean) {
+    this.myBoolean = myBoolean;
+  }
+
+
+  @Override
+  public boolean equals(java.lang.Object o) {
+    if (this == o) {
+      return true;
+    }
+    if (o == null || getClass() != o.getClass()) {
+      return false;
+    }
+    OuterComposite outerComposite = (OuterComposite) o;
+    return Objects.equals(this.myNumber, outerComposite.myNumber) &&
+        Objects.equals(this.myString, outerComposite.myString) &&
+        Objects.equals(this.myBoolean, outerComposite.myBoolean);
+  }
+
+  @Override
+  public int hashCode() {
+    return Objects.hash(myNumber, myString, myBoolean);
+  }
+
+
+  @Override
+  public String toString() {
+    StringBuilder sb = new StringBuilder();
+    sb.append("class OuterComposite {\n");
+    
+    sb.append("    myNumber: ").append(toIndentedString(myNumber)).append("\n");
+    sb.append("    myString: ").append(toIndentedString(myString)).append("\n");
+    sb.append("    myBoolean: ").append(toIndentedString(myBoolean)).append("\n");
+    sb.append("}");
+    return sb.toString();
+  }
+
+  /**
+   * Convert the given object to string with each line indented by 4 spaces
+   * (except the first line).
+   */
+  private String toIndentedString(java.lang.Object o) {
+    if (o == null) {
+      return "null";
+    }
+    return o.toString().replace("\n", "\n    ");
+  }
+  
+}
+