Sp/better handling of errors (#60)

* POC for how to handle error responses better

* refactor

* fix test case, start putting together new test cases

* cleanup

* wrap up refactoring

* Update documentation

* update docs

3_0_0_migration_notes.MD

@@ -1,6 +1,6 @@
 # Pardot Java API Client 2.x.x to 3.0.0 Migration Guide
 
-## Authentication & Configuration Breaking Changes
+## Breaking Change : Authentication & Configuration
 
 In order to properly support the transition of the Pardot API from authenticating using Pardot username, password, and user keys, to 
 Salesforce Single Signon, several breaking changes were made to how you configure the Pardot API Client.
@@ -48,4 +48,97 @@ final ConfigurationBuilder configuration = Configuration.newBuilder()
 final PardotClient client = new PardotClient(configuration);
 ```
 
-See [Offical Pardot Developer Documentation](https://developer.pardot.com/kb/authentication/) and [Salesforce OAuth Setup](https://help.salesforce.com/articleView?id=remoteaccess_oauth_flows.htm) for details on how to obtain the above required properties.
+See [Offical Pardot Developer Documentation](https://developer.pardot.com/kb/authentication/) and [Salesforce OAuth Setup](https://help.salesforce.com/articleView?id=remoteaccess_oauth_flows.htm) for details on how to obtain the above required properties.
+
+## Breaking Change : Read request methods now return Optionals
+
+Previously methods on `PardotClient` for reading objects (such as `PardotClient.readProspect()`, `PardotClient.readCampaign()`, etc...) 
+either returned the object you wished to retrieve, or threw an `InvalidRequestException` if the API returned a response stating that the record 
+could not be found.
+
+This often led to code like:
+```java
+// Try to lookup prospect by Email.
+Prospect myProspect = null;
+try {
+    myProspect = client.prospectRead(new ProspectReadRequest()
+        .selectByEmail("[email protected]")
+    );
+} catch (final InvalidRequestException exception) {
+    // Prospect could not be found. Swallow exception.  
+}
+
+// Handle prospect if found
+if (myProspect != null) {
+    ...
+}
+```
+
+These methods now return `Optional<T>`,which means you no longer need to catch and handle `InvalidRequestException` 
+when an object is unable to be found in the API.  The above example code can be simplified to:
+
+```java
+// Check if the Optional is present
+final Optional<Prospect> prospectResponse = client.prospectRead(new ProspectReadRequest()
+    .selectByEmail("[email protected]")
+);
+if (prospectResponse.isPresent()) {
+    final Prospect myProspect = prospectResponse.get()
+}
+
+// Or even better by using the methods available on Optional
+client.prospectRead(new ProspectReadRequest()
+    .selectByEmail('[email protected]')
+).ifPresent((prospect) -> {
+    // Make use of prospect if found
+    logger.info("Found prospect: {}", prospect.getEmail());
+});
+```
+
+## Breaking Change : Delete request methods no longer return boolean
+
+Previously methods on `PardotClient` for deleting objects (such as `PardotClient.deleteProspect()`, `PardotClient.deleteCampaign()`, etc...) 
+always returned a value of `true` regardless if the delete request was successful or not.  Version 3.0.0 changes the return type for these methods 
+to a type of `Result<Boolean>`.  The [Result](src/main/java/com/darksci/pardot/api/response/Result.java) object
+allows for returning a successful response (value of boolean `true`) as well as an [ErrorResponse](src/main/java/com/darksci/pardot/api/response/ErrorResponse.java) 
+instance if the request was not successful.
+
+The quick way to simply migrate your code:  
+
+```java
+// Code that looked like the following:
+final boolean result = client.userDelete(deleteRequest);
+// or
+if (client.userDelete(deleteRequest)) {
+
+// Now should look like:
+final boolean result = client.userDelete(deleteRequest).isSuccess();
+// or
+if (client.userDelete(deleteRequest.isSuccess())) {
+```
+
+But this new return type also gives you additional flexibility to handle errors more gracefully:
+```java
+// Handle success conditions:
+client
+    .userDelete(deleteRequest)
+    .ifSuccess((success) -> logger.info("Successfully deleted user!"));
+
+// Handle error conditions:
+client
+    .userDelete(deleteRequest)
+    .ifError((error -> logger.info("Failed to delete user: {}", error.getMessage())));
+
+// Or handle both cases:
+client
+    .userDelete(deleteRequest)
+    .handle(
+        (success) -> {
+            logger.info("Successfully deleted user!");
+            return true;
+        },
+        (error) -> {
+            logger.info("Error deleting user: {}", error.getMessage());
+            return false;
+        });
+```

CHANGELOG.md

@@ -3,10 +3,13 @@ The format is based on [Keep a Changelog](http://keepachangelog.com/)
 and this project adheres to [Semantic Versioning](http://semver.org/).
 
 ## 3.0.0 (UNRELEASED)
+
+### Breaking Changes
+This release has several breaking changes. See [3.0.0 Migration Notes](3_0_0_migration_notes.MD) for details on breaking changes and how to upgrade.
+
 - [ISSUE-58](https://github.com/Crim/pardot-java-client/issues/58) Add support for Salesforce SSO authentication.
+- [PR-60](https://github.com/Crim/pardot-java-client/pull/60) Alters return values from `PardotClient.readXYZ()` and `PardotClient.deleteXYZ()` to allow for better error handling.
 
-### Breaking Change
-See [3.0.0 Migration Notes](3_0_0_migration_notes.MD) for details on breaking changes and how to upgrade.
 
 ## 2.1.0 (07/30/2020)
 - [ISSUE-56](https://github.com/Crim/pardot-java-client/issues/56) Adds support for Dynamic Content.

src/main/java/com/darksci/pardot/api/InvalidRequestException.java

@@ -23,6 +23,11 @@
 public class InvalidRequestException extends RuntimeException {
     private final int errorCode;
 
+    /**
+     * Constructor.
+     * @param message Error message returned by Pardot API.
+     * @param errorCode Error code returned by Pardot API.
+     */
     public InvalidRequestException(final String message, final int errorCode) {
         super(message);
         this.errorCode = errorCode;