[Check If a Specified Key Exists in a Given S3 Bucket using Java] added code examples (#13775)

* [Check If a Specified Key Exists in a Given S3 Bucket using Java]] added code examples for

change test name

remove link from README.md

* - used env variables for AWS credentials
- used codestyle profile of baledung

aws-modules/aws-s3/src/main/java/com/baeldung/s3/AWSS3ObjectUtils.java

@@ -0,0 +1,42 @@
+package com.baeldung.s3;
+
+import org.apache.http.HttpStatus;
+
+import com.amazonaws.AmazonServiceException;
+import com.amazonaws.services.s3.AmazonS3;
+
+public class AWSS3ObjectUtils {
+
+    private AmazonS3 s3Client;
+
+    public AWSS3ObjectUtils(AmazonS3 s3client) {
+        this.s3Client = s3client;
+    }
+
+    public boolean doesObjectExistByDefaultMethod(String bucket, String key) {
+        return s3Client.doesObjectExist(bucket, key);
+    }
+
+    public boolean doesObjectExistByListObjects(String bucket, String key) {
+        return s3Client.listObjects(bucket)
+            .getObjectSummaries()
+            .stream()
+            .filter(s3ObjectSummary -> s3ObjectSummary.getKey()
+                .equals(key))
+            .findFirst()
+            .isPresent();
+    }
+
+    public boolean doesObjectExistByMetaData(String bucket, String key) {
+        try {
+            s3Client.getObjectMetadata(bucket, key);
+            return true;
+        } catch (AmazonServiceException e) {
+            if (e.getStatusCode() == HttpStatus.SC_NOT_FOUND) {
+                return false;
+            } else {
+                throw e;
+            }
+        }
+    }
+}

aws-modules/aws-s3/src/test/java/com/baeldung/s3/AWSS3ObjectIntegrationTest.java

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+package com.baeldung.s3;
+
+import static org.junit.jupiter.api.Assertions.assertTrue;
+
+import org.junit.Before;
+import org.junit.Test;
+
+import com.amazonaws.auth.EnvironmentVariableCredentialsProvider;
+import com.amazonaws.regions.Regions;
+import com.amazonaws.services.s3.AmazonS3;
+import com.amazonaws.services.s3.AmazonS3ClientBuilder;
+
+public class AWSS3ObjectIntegrationTest {
+
+    private static final String BUCKET = "your-bucket";
+    private static final String KEY_THAT_EXIST = "your-key-that-exist";
+    private AWSS3ObjectUtils s3ObjectUtils;
+
+    @Before
+    public void setUp() {
+        AmazonS3 client = AmazonS3ClientBuilder.standard()
+            .withRegion(Regions.DEFAULT_REGION)
+            .withCredentials(new EnvironmentVariableCredentialsProvider())
+            .build();
+
+        s3ObjectUtils = new AWSS3ObjectUtils(client);
+    }
+
+    @Test
+    public void whenVerifyIfObjectExistByDefaultMethod_thenCorrect() {
+        assertTrue(s3ObjectUtils.doesObjectExistByDefaultMethod(BUCKET, KEY_THAT_EXIST), "Key: " + KEY_THAT_EXIST + " doesn't exist");
+
+    }
+
+    @Test
+    public void whenVerifyIfObjectExistByListObjects_thenCorrect() {
+        assertTrue(s3ObjectUtils.doesObjectExistByListObjects(BUCKET, KEY_THAT_EXIST), "Key: " + KEY_THAT_EXIST + " doesn't exist");
+    }
+
+    @Test
+    public void whenVerifyIfObjectExistByMetaData_thenCorrect() {
+        assertTrue(s3ObjectUtils.doesObjectExistByMetaData(BUCKET, KEY_THAT_EXIST), "Key: " + KEY_THAT_EXIST + " doesn't exist");
+    }
+}