Java is one of the most popular programming languages for enterprise-level applications. One of its strengths is its ability to connect different layers and components of an application, making it easier to maintain and modify in the future. However, this connection requires the use of a lot of data transfer objects (DTOs), which can become cumbersome and time-consuming to create and maintain. This is where the Java modelmapper class comes in handy.
The Java modelmapper class is an open-source library that allows developers to map DTOs to domain entities and vice versa. It is easy to use and can help reduce the amount of time and code required for these mappings. This article will provide a brief introduction to the modelmapper class and provide some code examples to show how it can be used.
What is ModelMapper?
ModelMapper is a Java library that automates the mapping between DTOs and domain entities. It provides a simple and flexible API that allows developers to define custom mapping rules, and it uses reflection to automatically map fields with the same name and type between objects. This means that you don't need to manually populate every field of your DTO or entity. You can simply define the mapping rules once and let ModelMapper do the rest.
In addition to basic mapping, ModelMapper also supports complex mappings, such as nested objects, collections, and inheritance. It also supports different mapping strategies, such as field-level access and method-level access.
The ModelMapper class is thread-safe and can be used in multi-threaded environments without issue. It is licensed under the Apache 2.0 license and is available on Maven Central.
How to Use ModelMapper
Let's take a look at some code examples to see how easy it is to use ModelMapper.
Example 1: Basic Mapping
Suppose we have a DTO class called EmployeeDTO that contains some basic information about an employee, such as their name, email, and phone number.
public class EmployeeDTO {
private String name;
private String email;
private String phone;
// getters and setters
}
Now, let's say we want to map this DTO to a domain entity class called Employee.
public class Employee {
private String name;
private String email;
private String phone;
private Date hireDate;
// getters and setters
}
To map the DTO to the entity, we can create an instance of the ModelMapper class and call its map() method, passing in the source object (the DTO) and the destination type (the entity).
ModelMapper mapper = new ModelMapper();
EmployeeDTO employeeDTO = new EmployeeDTO();
// populate employeeDTO
Employee employee = mapper.map(employeeDTO, Employee.class);
That's it! ModelMapper will automatically map the fields with the same name and type between the DTO and the entity. In this case, it will map the name, email, and phone fields.
Example 2: Custom Mapping Rules
Suppose we want to map a DTO class called OrderDTO to a domain entity class called Order. The DTO contains a customer name field, while the entity contains separate firstName and lastName fields.
public class OrderDTO {
private String customerName;
private List
// getters and setters
}
public class Order {
private String firstName;
private String lastName;
private List
// getters and setters
}
To map the customerName field to the separate firstName and lastName fields, we can define a custom mapping rule using ModelMapper's TypeMap class.
ModelMapper mapper = new ModelMapper();
TypeMap<OrderDTO, Order> typeMap = mapper.createTypeMap(OrderDTO.class, Order.class);
typeMap.addMappings(m -> m.map(OrderDTO::getCustomerName, Order::setFirstName));
typeMap.addMappings(m -> m.map(src -> "", Order::setLastName)); // set the last name to empty string
// map the DTO to the entity
OrderDTO orderDTO = new OrderDTO();
// populate orderDTO
Order order = mapper.map(orderDTO, Order.class);
In this example, we create a TypeMap object for the OrderDTO and Order classes and add two mapping rules. The first rule maps the customerName field to the firstName field using a method reference. The second rule sets the lastName field to an empty string, since we don't have that information in the DTO.
Example 3: Complex Mapping
ModelMapper can also handle complex mappings, such as nested objects, collections, and inheritance. Let's look at an example of mapping a DTO class that contains a collection of child objects to a domain entity.
Suppose we have a DTO class called ParentDTO that contains a collection of ChildDTO objects.
public class ParentDTO {
private List
// getters and setters
}
public class ChildDTO {
private String name;
private int age;
// getters and setters
}
We also have a domain entity class called Parent that contains a list of Child objects.
public class Parent {
private List
// getters and setters
}
public class Child {
private String name;
private int age;
// getters and setters
}
To map the ParentDTO to the Parent entity, we can simply create a TypeMap object and call the map() method for each ChildDTO in the children list.
ModelMapper mapper = new ModelMapper();
TypeMap<ChildDTO, Child> childTypeMap = mapper.createTypeMap(ChildDTO.class, Child.class);
TypeMap<ParentDTO, Parent> parentTypeMap = mapper.createTypeMap(ParentDTO.class, Parent.class);
parentTypeMap.addMappings(m -> m.map(src -> src.getChildren().stream().map(childDto -> childTypeMap.map(childDto)), Parent::setChildren));
// map the DTO to the entity
ParentDTO parentDTO = new ParentDTO();
// populate parentDTO
Parent parent = mapper.map(parentDTO, Parent.class);
In this example, we create a TypeMap object for the ChildDTO and Child classes, and another TypeMap object for the ParentDTO and Parent classes. We define a mapping rule for the children list using a lambda expression that maps each ChildDTO to a Child object using the childTypeMap. Finally, we map the ParentDTO to the Parent entity using the TypeMap object we just created.
Conclusion
The Java modelmapper class is a powerful library that can save developers time and effort when mapping DTOs to entities and vice versa. It provides a simple and flexible API that can handle basic and complex mapping scenarios, and it is licensed under the Apache 2.0 license.
In this article, we have provided a brief introduction to ModelMapper and some code examples to show how it can be used in different scenarios. We encourage you to explore ModelMapper further and see how it can help simplify your code and improve the maintainability of your Java applications.
let's dive deeper into some of the topics we covered earlier.
Custom Mapping Rules
Custom mapping rules allow developers to define more complex mapping scenarios that modelmapper can't handle automatically. In the example we provided earlier, we mapped a DTO class called OrderDTO to a domain entity class called Order. The DTO contained a customerName field, while the entity contained separate firstName and lastName fields. To map the customerName field to the separate firstName and lastName fields, we defined a custom mapping rule using ModelMapper's TypeMap class.
Custom mapping rules can be defined in different ways. One way is to use lambda expressions that take the source object as input and return the destination object. Another way is to use method references that map a specific field or property in the source object to a specific field or property in the destination object. The TypeMap class provides a flexible API that can handle a wide range of mapping scenarios.
Complex Mappings
ModelMapper can handle complex mapping scenarios, such as nested objects, collections, and inheritance. In the example we provided earlier, we mapped a DTO class called ParentDTO that contained a collection of ChildDTO objects to a domain entity class called Parent that contained a list of Child objects. To map the ParentDTO to the Parent entity, we created a TypeMap object and called the map() method for each ChildDTO in the children list.
In more complex scenarios, ModelMapper can use recursion to map nested objects and collections. For example, if a DTO class contains a collection of objects that themselves contain nested objects or collections, ModelMapper will automatically map those objects and collections as well.
Configuring ModelMapper
ModelMapper is highly configurable and provides a wide range of options for controlling its behavior. For example, developers can customize the mapping strategy (field-level access or method-level access), specify custom type converters, and define naming conventions for properties and fields.
To configure ModelMapper, developers can use a Configuration object and its various methods to set property and field matching strategies, configure lifecycle callbacks, and customize type conversion. They can also use the addMappings() method to specify custom mapping rules and apply other customization options.
Best Practices
When using ModelMapper, it's important to follow some best practices to ensure that the mappings are accurate, maintainable, and efficient. Here are some best practices to keep in mind:
-
Define clear and consistent naming conventions for properties and fields in your DTO and entity classes to make the mapping process easier and more predictable.
-
Use custom mapping rules sparingly, and only when necessary to handle complex mapping scenarios that ModelMapper can't handle automatically.
-
Avoid using ModelMapper to perform transformations or business logic beyond simple mapping. Instead, use it to simplify the mapping process and reduce boilerplate code.
-
Review and test your mappings regularly to make sure they are accurate and maintainable, especially as your application grows and changes over time.
Conclusion
The Java modelmapper class is a powerful library that can save developers a lot of time and effort when mapping DTOs to entities and vice versa. It provides a simple and flexible API that can handle basic and complex mapping scenarios, and it's highly configurable and customizable.
By following best practices and using ModelMapper effectively, developers can simplify the mapping process and improve the maintainability and efficiency of their Java applications. We hope this article has provided a helpful introduction to ModelMapper and some good tips for getting the most out of it.
Popular questions
Q1. What is the Java modelmapper class?
A1. The Java modelmapper class is an open-source library that allows developers to map DTOs to domain entities and vice versa. It automates the mapping process and reduces the amount of time and code required for these mappings.
Q2. How can custom mapping rules be defined using ModelMapper?
A2. Custom mapping rules can be defined using lambda expressions that take the source object as input and return the destination object. Another way is to use method references that map a specific field or property in the source object to a specific field or property in the destination object. The TypeMap class provides a flexible API that can handle a wide range of mapping scenarios.
Q3. What are some best practices for using ModelMapper?
A3. Some best practices for using ModelMapper include defining clear and consistent naming conventions, using custom mapping rules sparingly, avoiding using ModelMapper for transformations or business logic beyond simple mapping, and reviewing and testing mappings regularly.
Q4. How can complex mapping scenarios be handled using ModelMapper?
A4. ModelMapper can handle complex mapping scenarios, such as nested objects, collections, and inheritance. It can use recursion to map nested objects and collections automatically.
Q5. How is ModelMapper configured?
A5. ModelMapper is highly configurable and provides a wide range of options for controlling its behavior. Developers can use a Configuration object and its various methods to set property and field matching strategies, configure lifecycle callbacks, and customize type conversion. They can also use the addMappings() method to specify custom mapping rules and apply other customization options.
Tag
Mapping
