Show more informative error message on parsing error

src/main/kotlin/org/springdoc/openapi/gradle/plugin/OpenApiGeneratorTask.kt

@@ -2,6 +2,7 @@ package org.springdoc.openapi.gradle.plugin
 
 import com.google.gson.GsonBuilder
 import com.google.gson.JsonObject
+import com.google.gson.JsonSyntaxException
 import org.awaitility.Durations
 import org.awaitility.core.ConditionTimeoutException
 import org.awaitility.kotlin.*
@@ -95,7 +96,12 @@ open class OpenApiGeneratorTask : DefaultTask() {
 
     private fun prettifyJson(response: String): String {
         val gson = GsonBuilder().setPrettyPrinting().create()
-        val googleJsonObject = gson.fromJson(response, JsonObject::class.java)
-        return gson.toJson(googleJsonObject)
+        try {
+            val googleJsonObject = gson.fromJson(response, JsonObject::class.java)
+            return gson.toJson(googleJsonObject)
+        } catch (e: RuntimeException) {
+            throw JsonSyntaxException("Failed to parse the API docs response string. " +
+                    "Please ensure that the response is in the correct format. response=$response", e)
+        }
     }
 }

src/test/kotlin/org/springdoc/openapi/gradle/plugin/OpenApiGradlePluginTest.kt

@@ -11,8 +11,11 @@ import org.gradle.testkit.runner.GradleRunner
 import org.gradle.testkit.runner.TaskOutcome
 import org.junit.jupiter.api.Assertions.assertEquals
 import org.junit.jupiter.api.Assertions.assertFalse
+import org.junit.jupiter.api.Assertions.assertNotNull
 import org.junit.jupiter.api.BeforeEach
 import org.junit.jupiter.api.Test
+import org.slf4j.Logger
+import org.slf4j.LoggerFactory
 import java.io.File
 import java.io.FileReader
 import java.nio.file.Files
@@ -47,6 +50,10 @@ class OpenApiGradlePluginTest {
         }
     """.trimIndent()
 
+    companion object {
+        val logger: Logger = LoggerFactory.getLogger(OpenApiGradlePluginTest::class.java)
+    }
+
     @BeforeEach
     fun createTemporaryAcceptanceProjectFromTemplate() {
         File(javaClass.classLoader.getResource("acceptance-project")!!.path).copyRecursively(projectTestDir)
@@ -278,6 +285,26 @@ class OpenApiGradlePluginTest {
         assertOpenApiJsonFile(2, outputJsonFileNameGroupB)
     }
 
+    @Test
+    fun `using invalid doc url`() {
+        buildFile.writeText(
+            """$baseBuildGradle
+            openApi{
+                apiDocsUrl = "http://localhost:8080/hello/world"
+            }
+        """.trimMargin()
+        )
+
+        try {
+            openApiDocsTask(runTheBuild())
+        } catch (e: RuntimeException) {
+            logger.error(e.message)
+            assertNotNull(e.message?.lines()?.find { it.contains(
+                "Failed to parse the API docs response string. " +
+                    "Please ensure that the response is in the correct format.") })
+        }
+    }
+
     private fun runTheBuild(vararg additionalArguments: String = emptyArray()) = GradleRunner.create()
         .withProjectDir(projectTestDir)
         .withArguments("clean", "generateOpenApiDocs", *additionalArguments)

src/test/resources/acceptance-project/src/main/java/com/example/demo/endpoints/HelloWorldController.java

@@ -1,12 +1,16 @@
 package com.example.demo.endpoints;
 
 import org.springframework.web.bind.annotation.GetMapping;
+import org.springframework.web.bind.annotation.RequestMapping;
+import org.springframework.web.bind.annotation.ResponseBody;
 import org.springframework.web.bind.annotation.RestController;
 
 @RestController("/hello")
+@RequestMapping("/hello")
 public class HelloWorldController {
 
     @GetMapping("/world")
+    @ResponseBody
     public String helloWorld() {
         return "Hello World!";
     }