[recommend an entity class conversion tool mapstruct, which is powerful and easy to use]

1. What is? MapStruct

1.1 JavaBean Trouble

For code JavaBean Conversion between , It's been bothering me for a long time . When I was developing, I saw a lot of business code JavaBean Mutual transformation between , Very influential perception , But it has to exist . One way I thought about it later was through reflection , Or write a lot of converters .

The first method of reflection is really convenient , But now whether it's BeanUtils, BeanCopier When using reflection, it will affect the performance . Although we can cache reflection information to improve performance . But words like this , You need the same type and name to map , A lot of times , Because different teams use different terms , Still need a lot of manual set/get And so on .

The second is that it will be a waste of time , And when you add new fields, you also need to modify the methods . however , Because there's no need to reflect , Its performance is very high . recommend ：Java Advanced video resources

1.2 MapStruct Change

MapSturct It's a generation type security , High performance and independent JavaBean The annotation processor that maps the code （annotation processor）.

• Annotation processor
• Can generate JavaBean The mapping code between
• Type safety , High performance , No dependency

2.MapStruct introduction

2.1 Add dependency

2.2 po class

2.3 dto class

2.4 Create adapters

2.5 The test method

2.6 Running effect

2.7 View compiled class

The bottom layer is completed by automatic value assignment

3.MapStruct Advantage analysis

3.1 High performance

This is relative to reflection , Reflection needs to read bytecode content , It will cost a lot . And by MapStruct To generate code , It's similar to hand writing . Speed can be guaranteed .

3.2 Easy to use

If it's completely mapped , It's certainly not as easy to use as reflection . Use similar BeanUtils These tools are done in one sentence . however , If a special match is needed （ Special type conversion , Many to one conversion, etc ）, It's relatively simple .

Basically , When you use it , We just need to declare an interface , Write the corresponding method under the interface , You can use it . Of course , If there are special circumstances , It's something that needs extra treatment . recommend ：Java Advanced video resources

3.3 Code independent

The generated code is opposite , No runtime dependencies .

3.4 Easy to debug

In the code we generated , We can do it easily debug.

4.MapStruct Use cases

4.1 Property names are the same

When implementing a class , If the attribute names are the same , The corresponding transformation will be carried out . In this way , We can quickly write the transformation method .（ Introductory cases ）

4.2 Property names are different

Property names are different , When it's time for mutual transformation , Then we can go through @Mapping  Annotation to translate .

• source Docking that needs to be converted , It's usually a reference
• target Butt joint of conversion , Usually out of reference
• ignore Ignore , Default false Don't ignore , It needs to be ignored and set to true
• defaultValue The default value is
• expressions Some simple transformation relations can be constructed through expressions . Although the design wants to be compatible with many languages , But at present, it can only write Java Code .

@Mappings({
            @Mapping(source = "birthdate", target = "birth"),// Inconsistent attribute name mapping 
            @Mapping(target = "birthformat", expression = "java(org.apache.commons.lang3.time.DateFormatUtils.format(person.getBirthdate(),\"yyyy-MM-dd HH:mm:ss\"))"),// Custom attributes can be accessed through java Code mapping 
    })
public PersonVo PersonToPersonVo(Person person);

Here is a demonstration of how to use TimeAndFormat Yes time and format operation , Here you must specify what you want to use Java The full package name of the class , Otherwise, I don't know which one you use when compiling Java class , Will report a mistake .

4.3 Convert non base type properties

If subUser And subUserDto If the field name is the same, you can configure it directly ( object type , Include list)

4.4 Mapper Use custom transformation in

occasionally , For some types , It can't be handled in the form of a code generator . that , You need a custom method to transform . Now , We can be at the interface （ Same interface , There are other calls in the future Mapper Methods ） The default method is defined in （Java8 And after ）.

There can only be one default The method of decoration

4.5 One more turn

We need to transform multiple objects into one scene in the actual business .MapStruct Of course, it also supports the operation of "multi to one" . recommend ：Java Advanced video resources

4.5.1 Follow the principles

• When more than one object , One of them is null, Will return directly to null
• Like a one-to-one conversion , Property automatically matches by name . therefore , Those with the same name and type do not need special treatment
• When there are more than one original object , When there is an attribute with the same name , Need to pass through @Mapping Note to specify , To avoid ambiguity （ No error will be reported ）. As above name

Properties can also be assigned directly from the parameters passed in

4.6 to update Bean object

occasionally , We don't want to go back to a new Bean object , Instead, I want to update some properties of the incoming object . This is often used in practice .

4.7 map mapping

4.8 Multi level nesting

Only need mapper You can define relevant type conversion methods in the interface ,list Type also applies

4.8.1 The way 1

4.8.2 The way 2

adopt uses Configure type conversion

5. obtain mapper

5.1 adopt Mapper The factory gets

We all passed  Mappers.getMapper(xxx.class)  In a way that corresponds to Mapper Acquisition . This method is through Mapper The factory gets .

If this is the way , The Convention is to define an instance of the interface itself within the interface INSTANCE, In order to obtain the corresponding instance conveniently .

So when it's called , We don't need to instantiate objects repeatedly . It's like this

Target target = SourceMapper.INSTANCE.source2target(source);

5.2 Use dependency injection

about Web Development , Dependency injection should be familiar .MapSturct It also supports the use of dependency injection , It is also recommended to use dependency injection .

@Mapper(componentModel = "spring")

5.3 Dependency injection strategy

You can choose to inject... By constructing methods or attributes , The default is property injection .

Use like this

@Mapper(componentModel = "cdi" injectionStrategy = InjectionStrategy.CONSTRUCTOR)

5.4 Custom type conversion

occasionally , There may be such a problem in object transformation , The type in the source object is Boolean type , And the target object type is String type , This can be done by @Mapper Of uses Property to implement ：

It should be noted that , If you use something like spring Such an environment ,Mapper introduce uses Class instances will be automatically injected , So this class should also be included in Spring Containers