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About Sezin Karli

Mathematics Engineer & Computer Scientist with a passion for software development. Avid learner for new technologies. Currently working as Senior Software Engineer at Sahibinden.com.

Rocking with mongodb on spring boot

I’m a fan of Spring Boot and here’s my mongodb example project on Spring Boot. Most of the mongodb example projects are so basic that you won’t go far with them. You can search for plain Spring Data examples but they can get much complex than you’d like. So here’s mine.
Here’s the pom I’ll use.

<!--?xml version="1.0" encoding="UTF-8"?-->
<project xmlns="http://maven.apache.org/POM/4.0.0" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:schemalocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd">


    <!-- Inherit defaults from Spring Boot -->



    <!-- Needed for fat jar -->

            <name>Spring Snapshots</name>


The only dependency I need is “spring-boot-starter-data-mongodb” which contains all necessary dependencies for a spring boot mongodb project. Next is the model for my collection. Document annotation points to my collection named “products”. It is need only if your model name does not match your collection name. You can see a field annotation which maps the field name in the collection to the model’s field name.

@Document(collection = "products")
public class Product {
    private String id;
    private String sku;

    @Field(value = "material_name")
    private String materialName;

    private Double price;
    private Integer availability;

    public String getId() {
        return id;

    public void setId(String id) {
        this.id = id;

    public String getSku() {
        return sku;

    public void setSku(String sku) {
        this.sku = sku;

    public String getMaterialName() {
        return materialName;

    public void setMaterialName(String materialName) {
        this.materialName = materialName;

    public Double getPrice() {
        return price;

    public void setPrice(Double price) {
        this.price = price;

    public Integer getAvailability() {
        return availability;

    public void setAvailability(Integer availability) {
        this.availability = availability;

    public String toString() {
        return "Product{" +
                "id='" + id + '\'' +
                ", sku='" + sku + '\'' +
                ", materialName='" + materialName + '\'' +
                ", price=" + price +
                ", availability=" + availability +

Not we will need a DAO layer to manipulate my data. MongoRepository is the interface I should implement if I want to use autogenerated find methods in my DAO layer and I want that. Every field of my model can be queried with these autogenerated methods. For a complete list of method name syntax check here. My query below will take a sku name and search my collection for this name and return the matching ones.

public interface ProductRepository extends MongoRepository < Product, String >{
    public List < Product > findBySku(String sku);

Now I’ll introduce a Service which will call my DAO interface. But wait a minute, I didn’t implement this interface and wrote necessary code for fetching the models right? Yep, these methods are autogenerated and I don’t need an implementation for this interface.

public class ProductService {
    private ProductRepository repository;

    public List < Product > getSku(String sku){
        return repository.findBySku(sku);

Next, lets launch our Boot example. Here’s our main class:

public class BootMongoDB implements CommandLineRunner {

    private ProductService productService;

    private static final Logger logger = LoggerFactory.getLogger(BootMongoDB.class);

    public void run(String... args) throws Exception {
        List < Product > sku = productService.getSku("NEX.6");
        logger.info("result of getSku is {}", sku);

    public static void main(String[] args) throws Exception {
        SpringApplication.run(BootMongoDB.class, args);

If you have a connection to a mongodb instance and a sku matching to the name you searched than you should see one or more Products as a result. What we did was quite basic. What if I want more complex queries? For instance if I want a specific sku with an availability equal to “1”? I can’t do it without using some @Query magic. So I’m updating my DAO class.

public interface ProductRepository extends MongoRepository < Product, String >{
    public List < Product > findBySku(String sku);

    @Query(value = "{sku: ?0, availability : 1}")
    public List < Product > findBySkuOnlyAvailables(String sku);

I provided a direct query for mongodb where sku in the signature of my method will be inserted to “?0” in the query and will be sent to mongodb. You can update your Service and then your main method to see if it works. You may not like writing queries which are not much readable if you’re not very familiar with mongodb’s syntax. Then this is the time for adding custom DAO classes. It’s not possible to add and use methods other than the autogenerated ones to ProductRepository. So we will add few classes and have a nice featured methods. Our repository class was named “ProductRepository”. We will add a new interface named “ProductRepositoryCustom” and a new method which will find available skus for the given name (twin of findBySkuOnlyAvailables method).

public interface ProductRepositoryCustom {
    public List < Product > findBySkuOnlyAvailablesCustom(String sku);

Then provide an implementation for this. Below you see that we inject ProductRepositoryCustom’s mongotemplate and do stuff with it. We create two criteria. First one is for the sku name and the second one is for availability.

public class ProductRepositoryImpl implements ProductRepositoryCustom {
    private MongoTemplate mongoTemplate;

    public List < Product > findBySkuOnlyAvailablesCustom(String sku) {
        Criteria criteria = Criteria.where("sku").is(sku).
        return mongoTemplate.find(Query.query(criteria), Product.class);

The last step for custom implemetation is the update of ProductRepository class. As you can see below the only update I need is the addition of my ProductRepositoryCustom so we can link both of them together. All this naming can sound a little stupid. But notice that although the name of your custom interface is not important, a change in the name of the implementation will result in the throw of an exception:

Invocation of init method failed; nested exception is org.springframework.data.mapping.PropertyReferenceException: No property only found for type String! Traversed path: Product.sku.

To fix this make sure that the name of your implementation class is “ProductRepositoryImpl” which is the concatenation of the name of the interface that extends MongoRepository and “Impl”.

public interface ProductRepository extends MongoRepository < Product, String>, ProductRepositoryCustom

If we add our new method to our Service layer:

public class ProductService {
    private ProductRepository repository;

    public List < Product > getSku(String sku){
        return repository.findBySku(sku);

    public List < Product > getAvailableSkuCustom(String sku){
        return repository.findBySkuOnlyAvailablesCustom(sku);

Then update our main class’ run method:

public void run(String... args) throws Exception {
        List < Product > sku = productService.getSku("NEX.6");
        logger.info("result of getSku is {}", sku);

        List < Product > availableSkuCustom = productService.getAvailableSkuCustom("NEX.6");
        logger.info("result of availableSkuCustom is {}", availableSkuCustom);

Again you must see something in the log! You can check the whole project on github.

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  1. How do you specifi the database name or URL?

    • If you use test database on your localhost there’s no need to specify.
      But if you don’t you add a single line to your application properties under resources.


      you can set your url such as this.

  2. I want to set read preference to my 3-member replica set. How to configure it using spring.data.mongodb.uri from java driver. I want to set “secondary preferred” read preference.

    • Direct from documentation:

      You can set spring.data.mongodb.uri property to change the URL and configure additional settings such as the replica set:

      spring.data.mongodb.uri=mongodb://user:[email protected]:12345,mongo2.example.com:23456/test

  3. When we store _id it is stored as ObjectId(“57ea86657b91bd2998ba3ffc”) rather than a plain String . Is there a way we can make it store a String.

  4. How do I store Mongodb values into an array list in java? ex; manually enter 20 names into Mongodb, now I want to create a forloop for each name in mongodb using java.
    For(name:AllName) {
    //do something

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