Exception Handling with @ExceptionHandler

Author: Rajeev Kumar Singh

src/main/java/com/example/webfluxdemo/controller/TweetController.java

@@ -1,8 +1,11 @@
 package com.example.webfluxdemo.controller;
 
+import com.example.webfluxdemo.exception.TweetNotFoundException;
 import com.example.webfluxdemo.model.Tweet;
+import com.example.webfluxdemo.payload.ErrorResponse;
 import com.example.webfluxdemo.repository.TweetRepository;
 import org.springframework.beans.factory.annotation.Autowired;
+import org.springframework.dao.DuplicateKeyException;
 import org.springframework.http.HttpStatus;
 import org.springframework.http.MediaType;
 import org.springframework.http.ResponseEntity;
@@ -33,7 +36,8 @@ public Mono<Tweet> createTweets(@Valid @RequestBody Tweet tweet) {
 
     @GetMapping("/tweets/{id}")
     public Mono<Tweet> getTweetById(@PathVariable(value = "id") String tweetId) {
-        return tweetRepository.findById(tweetId);
+        return tweetRepository.findById(tweetId)
+                .switchIfEmpty(Mono.error(new TweetNotFoundException("Tweet not found with id "+ tweetId)));
     }
 
     @PutMapping("/tweets/{id}")
@@ -65,4 +69,16 @@ public Flux<Tweet> streamAllTweets() {
         return tweetRepository.findAll();
     }
 
+
+    // Exception Handling Examples
+    @ExceptionHandler
+    public ResponseEntity handleDuplicateKeyException(DuplicateKeyException ex) {
+        return ResponseEntity.status(HttpStatus.CONFLICT).body(new ErrorResponse("A Tweet with the same text already exists"));
+    }
+
+    @ExceptionHandler
+    public ResponseEntity handleNotFoundException(TweetNotFoundException ex) {
+        return ResponseEntity.notFound().build();
+    }
+
 }

src/main/java/com/example/webfluxdemo/exception/TweetNotFoundException.java

@@ -0,0 +1,11 @@
+package com.example.webfluxdemo.exception;
+
+/**
+ * Created by rajeevkumarsingh on 22/10/17.
+ */
+public class TweetNotFoundException extends RuntimeException {
+
+    public TweetNotFoundException(String tweetId) {
+        super("Tweet not found with id " + tweetId);
+    }
+}

src/main/java/com/example/webfluxdemo/model/Tweet.java

@@ -2,6 +2,7 @@
 
 import org.hibernate.validator.constraints.NotBlank;
 import org.springframework.data.annotation.Id;
+import org.springframework.data.mongodb.core.index.Indexed;
 import org.springframework.data.mongodb.core.mapping.Document;
 
 import javax.validation.constraints.NotNull;
@@ -19,6 +20,7 @@ public class Tweet {
 
     @NotBlank
     @Size(max = 140)
+    @Indexed(unique = true)
     private String text;
 
     @NotNull

src/main/java/com/example/webfluxdemo/payload/ErrorResponse.java

@@ -0,0 +1,20 @@
+package com.example.webfluxdemo.payload;
+
+/**
+ * Created by rajeevkumarsingh on 22/10/17.
+ */
+public class ErrorResponse {
+    private String message;
+
+    public ErrorResponse(String message) {
+        this.message = message;
+    }
+
+    public String getMessage() {
+        return message;
+    }
+
+    public void setMessage(String message) {
+        this.message = message;
+    }
+}