REST APIs with Java, Spring Boot, and MongoDB

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git clone https://github.com/mongodb-developer/java-spring-boot-mongodb-starter

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package com.mongodb.starter;
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import [...]
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import static org.bson.codecs.configuration.CodecRegistries.fromProviders;
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import static org.bson.codecs.configuration.CodecRegistries.fromRegistries;
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@Configuration
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public class MongoDBConfiguration {
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    @Value("${spring.data.mongodb.uri}")
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    private String connectionString;
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    @Bean
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    public MongoClient mongoClient() {
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        CodecRegistry pojoCodecRegistry = fromProviders(PojoCodecProvider.builder().automatic(true).build());
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        CodecRegistry codecRegistry = fromRegistries(MongoClientSettings.getDefaultCodecRegistry(), pojoCodecRegistry);
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        return MongoClients.create(MongoClientSettings.builder()
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                                                      .applyConnectionString(new ConnectionString(connectionString))
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                                                      .codecRegistry(codecRegistry)
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                                                      .build());
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    }
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}

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private static final TransactionOptions txnOptions = TransactionOptions.builder()
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    .readPreference(ReadPreference.primary())
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    .readConcern(ReadConcern.MAJORITY)
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    .writeConcern(WriteConcern.MAJORITY)
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    .build();
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@Override
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public List<PersonEntity> saveAll(List<PersonEntity> personEntities) {
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    try (ClientSession clientSession = client.startSession()) {
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        return clientSession.withTransaction(() -> {
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            personEntities.forEach(p -> p.setId(new ObjectId()));
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            personCollection.insertMany(clientSession, personEntities);
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            return personEntities;
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        }, txnOptions);
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    }
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}

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@ExceptionHandler(RuntimeException.class)
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public final ResponseEntity<Exception> handleAllExceptions(RuntimeException e) {
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    logger.error("Internal server error.", e);
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    return new ResponseEntity<>(e, HttpStatus.INTERNAL_SERVER_ERROR);
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}

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@Override
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public double getAverageAge() {
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    List<Bson> pipeline = List.of(group(new BsonNull(), avg("averageAge", "$age")), project(excludeId()));
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    return personCollection.aggregate(pipeline, AverageAgeDTO.class).first().averageAge();
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}

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private MongoCollection<PersonEntity> personCollection;
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@PostConstruct
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void init() {
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    personCollection = client.getDatabase("test").getCollection("persons", PersonEntity.class);
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}

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<dependency>
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    <groupId>org.springdoc</groupId>
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    <artifactId>springdoc-openapi-starter-webmvc-ui</artifactId>
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    <version>2.2.0</version>
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</dependency>