Kotlin's use of the no Arg compiler plug-in in gradle

1、 Preface

Recently in use Kotlin+Spring Boot Write a backend project , Entity classes habitually use Kotlin Medium data class, however Spring Requires a parameterless constructor , Otherwise you might throw it java.sql.SQLDataException. To make data class Can generate a parameterless constructor , There are two ways to do ：

1. to data class Each parameter in the constructor of is assigned a default value . such as ：

data class User(
    @TableId(value = "id", type = IdType.AUTO)
    var id: Int?=-1,
    var userName: String?=null,  // user name 
    var age: Int?=null,  // Age 
    var password: String?=null,  // password 
    var name: String?=null,  // full name 
    var email: String?=null   // mailbox 
) : Serializable

2. Use the parameterless compiler plug-in no-arg. Let's take a look at this method .

2、 Specific steps

2.1 Add plug-in dependencies

First of all, it needs to be carried out at the beginning of the project build.gradle Add no-arg Plug in dependency , Version follows Kotlin Consistent versions of ：

plugins {
   	……
    id "org.jetbrains.kotlin.plugin.noarg" version "1.3.41"
}

I use it plugins In the form of , If you're using buildscript Blocks can be added in this way ：

buildscript {
    dependencies {
        classpath "org.jetbrains.kotlin:kotlin-noarg:1.3.41"
    }
}

apply plugin: "kotlin-noarg"

2.2 Specify the nonparametric annotation list

Tell the truth , This step is not easy to understand when reading official documents , Here I only describe my experience after my own practice . First create an annotation class , We can define the class name as NoArg：

annotation class NoArg

Then the most critical step came , Back to engineering build.gradle file , Add a list of nonparametric comments ：

noArg {
    annotation("com.lindroid.projectname.annotation.NoArg")
}

annotation The path in is what we created NoArg The package directory where the annotation class is located . The path must be written well , Don't make mistakes ！ At this point, the parameterless plug-in has been configured . We can do it in data class Add @NoArg annotation , In this way, the compiler can generate a parameterless constructor for it . An example is as follows ：

@NoArg
data class User(
    @TableId(value = "id", type = IdType.AUTO)
    var id: Int?,
    var userName: String?,  // user name 
    var age: Int?,  // Age 
    var password: String?,  // password 
    var name: String?,  // full name 
    var email: String?   // mailbox 
) : Serializable

2.3 kotlin-jpa Nonparametric annotation in

If you have added kotlin-jpa plug-in unit , Basically, there is no need to add a parameterless plug-in alone .kotlin-jpa The plug-in without parameters is packaged , When you use @Entity、@Embeddable And @MappedSuperclass These notes , By default, no Parameter annotation is supported .

3、 Reference article

Kotlin Official documents