Fix breaking changes in Render contract (#742)

* Fix breaking changes in Render contract
* Fix code review issue, update readme, add test, group render tests within one folder.
* Fix formatting

Author: DrSatyr

README.md

@@ -200,56 +200,37 @@ public class Main {
 #### HTML
 
 ```java
-String html = new HtmlRender("Changelog",
-        "http://deepoove.com/swagger-diff/stylesheets/demo.css")
-                .render(diff);
-
-try {
-    FileWriter fw = new FileWriter("testNewApi.html");
-    fw.write(html);
-    fw.close();
-} catch (IOException e) {
-    e.printStackTrace();
-}
+String htmlRender = new HtmlRender("Changelog", "http://deepoove.com/swagger-diff/stylesheets/demo.css");
+FileOutputStream outputStream = new FileOutputStream("testDiff.html");
+OutputStreamWriter outputStreamWriter = new OutputStreamWriter(outputStream);
+htmlRender.render(diff, outputStreamWriter);
 ```
 
 #### Markdown
 
 ```java
-String render = new MarkdownRender().render(diff);
-try {
-    FileWriter fw = new FileWriter("testDiff.md");
-    fw.write(render);
-    fw.close();
-} catch (IOException e) {
-    e.printStackTrace();
-}
+JsonRender markdownRender = new MarkdownRender();
+FileOutputStream outputStream = new FileOutputStream("testDiff.md");
+OutputStreamWriter outputStreamWriter = new OutputStreamWriter(outputStream);
+markdownRender.render(diff, outputStreamWriter);
 ```
 
 #### Asciidoc
 
 ```java
-String render = new AsciidocRender().render(diff);
-try {
-    FileWriter fw = new FileWriter("testDiff.adoc");
-    fw.write(render);
-    fw.close();
-} catch (IOException e) {
-    e.printStackTrace();
-}
+JsonRender asciidocRender = new AsciidocRender();
+FileOutputStream outputStream = new FileOutputStream("testDiff.adoc");
+OutputStreamWriter outputStreamWriter = new OutputStreamWriter(outputStream);
+asciidocRender.render(diff, outputStreamWriter);
 ```
 
 #### JSON
 
 ```java
-String render = new JsonRender().render(diff);
-try {
-    FileWriter fw = new FileWriter("testDiff.json");
-    fw.write(render);
-    fw.close();
-} catch (IOException e) {
-    e.printStackTrace();
-}
+JsonRender jsonRender = new JsonRender();
+FileOutputStream outputStream = new FileOutputStream("testDiff.json");
+OutputStreamWriter outputStreamWriter = new OutputStreamWriter(outputStream);
+jsonRender.render(diff, outputStreamWriter);
 ```
 
 ### Extensions

core/src/main/java/org/openapitools/openapidiff/core/output/Render.java

@@ -1,13 +1,45 @@
 package org.openapitools.openapidiff.core.output;
 
+import java.io.ByteArrayOutputStream;
 import java.io.IOException;
 import java.io.OutputStreamWriter;
 import org.openapitools.openapidiff.core.exception.RendererException;
 import org.openapitools.openapidiff.core.model.ChangedOpenApi;
 
 public interface Render {
 
-  void render(ChangedOpenApi diff, OutputStreamWriter outputStreamWriter);
+  /**
+   * render provided diff object
+   *
+   * @param diff diff object to render
+   * @param outputStreamWriter writer for rendered results
+   */
+  void render(ChangedOpenApi diff, OutputStreamWriter outputStreamWriter) throws RendererException;
+
+  /**
+   * render provided diff object
+   *
+   * @deprecated since 2.1.0, use {@link Render#render(ChangedOpenApi, OutputStreamWriter)} to avoid
+   *     massive String output issues. details <a
+   *     href="https://github.com/OpenAPITools/openapi-diff/issues/543">#543</a>
+   * @param diff diff object to render
+   * @return rendered output
+   */
+  @Deprecated
+  default String render(ChangedOpenApi diff) throws RendererException {
+    ByteArrayOutputStream byteArrayOutputStream = new ByteArrayOutputStream();
+    OutputStreamWriter outputStreamWriter = new OutputStreamWriter(byteArrayOutputStream);
+    render(diff, outputStreamWriter);
+    String result = byteArrayOutputStream.toString();
+
+    try {
+      outputStreamWriter.close();
+    } catch (IOException e) {
+      throw new RendererException(e);
+    }
+
+    return result;
+  }
 
   default void safelyAppend(OutputStreamWriter outputStreamWriter, String csq) {
     try {

core/src/test/java/org/openapitools/openapidiff/core/AsciidocRenderTest.java renamed to core/src/test/java/org/openapitools/openapidiff/core/output/AsciidocRenderTest.java

@@ -1,12 +1,12 @@
-package org.openapitools.openapidiff.core;
+package org.openapitools.openapidiff.core.output;
 
 import static org.assertj.core.api.Assertions.assertThat;
 
 import java.io.ByteArrayOutputStream;
 import java.io.OutputStreamWriter;
 import org.junit.jupiter.api.Test;
+import org.openapitools.openapidiff.core.OpenApiCompare;
 import org.openapitools.openapidiff.core.model.ChangedOpenApi;
-import org.openapitools.openapidiff.core.output.AsciidocRender;
 
 public class AsciidocRenderTest {
   @Test

core/src/test/java/org/openapitools/openapidiff/core/ConsoleRenderTest.java renamed to core/src/test/java/org/openapitools/openapidiff/core/output/ConsoleRenderTest.java

@@ -1,12 +1,12 @@
-package org.openapitools.openapidiff.core;
+package org.openapitools.openapidiff.core.output;
 
 import static org.assertj.core.api.Assertions.assertThat;
 
 import java.io.ByteArrayOutputStream;
 import java.io.OutputStreamWriter;
 import org.junit.jupiter.api.Test;
+import org.openapitools.openapidiff.core.OpenApiCompare;
 import org.openapitools.openapidiff.core.model.ChangedOpenApi;
-import org.openapitools.openapidiff.core.output.ConsoleRender;
 
 public class ConsoleRenderTest {
   @Test

core/src/test/java/org/openapitools/openapidiff/core/HtmlRenderTest.java renamed to core/src/test/java/org/openapitools/openapidiff/core/output/HtmlRenderTest.java

@@ -1,12 +1,12 @@
-package org.openapitools.openapidiff.core;
+package org.openapitools.openapidiff.core.output;
 
 import static org.assertj.core.api.Assertions.assertThat;
 
 import java.io.ByteArrayOutputStream;
 import java.io.OutputStreamWriter;
 import org.junit.jupiter.api.Test;
+import org.openapitools.openapidiff.core.OpenApiCompare;
 import org.openapitools.openapidiff.core.model.ChangedOpenApi;
-import org.openapitools.openapidiff.core.output.HtmlRender;
 
 public class HtmlRenderTest {
   @Test

core/src/test/java/org/openapitools/openapidiff/core/JsonRenderTest.java renamed to core/src/test/java/org/openapitools/openapidiff/core/output/JsonRenderTest.java

@@ -1,12 +1,12 @@
-package org.openapitools.openapidiff.core;
+package org.openapitools.openapidiff.core.output;
 
 import static org.assertj.core.api.Assertions.assertThat;
 
 import java.io.ByteArrayOutputStream;
 import java.io.OutputStreamWriter;
 import org.junit.jupiter.api.Test;
+import org.openapitools.openapidiff.core.OpenApiCompare;
 import org.openapitools.openapidiff.core.model.ChangedOpenApi;
-import org.openapitools.openapidiff.core.output.JsonRender;
 
 public class JsonRenderTest {
   @Test

core/src/test/java/org/openapitools/openapidiff/core/MarkdownRenderTest.java renamed to core/src/test/java/org/openapitools/openapidiff/core/output/MarkdownRenderTest.java

@@ -1,12 +1,12 @@
-package org.openapitools.openapidiff.core;
+package org.openapitools.openapidiff.core.output;
 
 import static org.assertj.core.api.Assertions.assertThat;
 
 import java.io.ByteArrayOutputStream;
 import java.io.OutputStreamWriter;
 import org.junit.jupiter.api.Test;
+import org.openapitools.openapidiff.core.OpenApiCompare;
 import org.openapitools.openapidiff.core.model.ChangedOpenApi;
-import org.openapitools.openapidiff.core.output.MarkdownRender;
 
 public class MarkdownRenderTest {
   @Test

core/src/test/java/org/openapitools/openapidiff/core/output/RenderTest.java

@@ -0,0 +1,27 @@
+package org.openapitools.openapidiff.core.output;
+
+import static org.assertj.core.api.AssertionsForClassTypes.assertThat;
+
+import java.io.IOException;
+import org.junit.jupiter.api.Test;
+import org.openapitools.openapidiff.core.exception.RendererException;
+import org.openapitools.openapidiff.core.model.ChangedOpenApi;
+
+class RenderTest {
+
+  private final Render testRenderImpl =
+      (diff, outputStreamWriter) -> {
+        try {
+          outputStreamWriter.write("Output");
+          outputStreamWriter.close();
+        } catch (IOException e) {
+          throw new RendererException(e);
+        }
+      };
+
+  @Test
+  void testDefaultRenderMethod() {
+    ChangedOpenApi diff = new ChangedOpenApi(null);
+    assertThat(testRenderImpl.render(diff)).isEqualTo("Output");
+  }
+}