springboot maven java 项目引入 kotlin 支持

缘起

在b站看到了一个短视频，介绍了 springboot maven java 项目引入 kotlin，感觉挺有意思，而且一直想对 kotlin 语言进行一些深入的学习，所以就蠢蠢欲动

前提准备

试验项目的话，就使用 mfi-server，一个非常简单的 springboot web 服务,用于MFi 获取 token。现在是由maven构建，咱们先试验加入 kotlin

实施

改造 POM 文件

maven 引入 kotlin 支持，第一步: (翻资料) 改造POM文件

原本的POM 文件如下:

<?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 https://maven.apache.org/xsd/maven-4.0.0.xsd">
    <modelVersion>4.0.0</modelVersion>
    <parent>
        <groupId>org.springframework.boot</groupId>
        <artifactId>spring-boot-starter-parent</artifactId>
        <version>3.0.6</version>
        <relativePath/> <!-- lookup parent from repository -->
    </parent>
    <groupId>dev.fromnowon</groupId>
    <artifactId>mfi-server</artifactId>
    <version>0.0.1-SNAPSHOT</version>
    <name>mfi-server</name>
    <description>mfi-server</description>
    <properties>
        <java.version>17</java.version>
    </properties>
    <dependencies>
        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter-web</artifactId>
        </dependency>
        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter-validation</artifactId>
        </dependency>
        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-configuration-processor</artifactId>
            <optional>true</optional>
        </dependency>
        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter-test</artifactId>
            <scope>test</scope>
        </dependency>
        <dependency>
            <groupId>org.springframework.retry</groupId>
            <artifactId>spring-retry</artifactId>
        </dependency>
        <dependency>
            <groupId>org.springframework</groupId>
            <artifactId>spring-aspects</artifactId>
        </dependency>
        <dependency>
            <groupId>org.projectlombok</groupId>
            <artifactId>lombok</artifactId>
            <optional>true</optional>
        </dependency>
        <dependency>
            <groupId>com.fasterxml.jackson.dataformat</groupId>
            <artifactId>jackson-dataformat-csv</artifactId>
        </dependency>
        <dependency>
            <scope>compile</scope>
            <groupId>org.apache.poi</groupId>
            <artifactId>poi-ooxml</artifactId>
            <version>5.2.2</version>
        </dependency>
    </dependencies>

    <build>
        <plugins>
            <plugin>
                <groupId>org.springframework.boot</groupId>
                <artifactId>spring-boot-maven-plugin</artifactId>
                <configuration>
                    <excludes>
                        <exclude>
                            <groupId>org.projectlombok</groupId>
                            <artifactId>lombok</artifactId>
                        </exclude>
                    </excludes>
                </configuration>
            </plugin>
        </plugins>
    </build>

</project>

还是看一下资料吧。。。

kotlin: compile-kotlin-and-java-sources

另外可以看一下平台-JVM部分:

spring framework 中对于 kotlin 语言的支持： spring framework kotlin

其中有几个重要的点:

• 关于 jackson-module-kotlin 依赖:

• spring 项目中需要额外关注一下: Spring Projects in Kotlin、Spring support、Kotlin Support
  里面提到了很重要的插件: kotlin-maven-allopen 和 kotlin-maven-noarg

照猫画虎,改造后的POM如下:

<?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 https://maven.apache.org/xsd/maven-4.0.0.xsd">
    <modelVersion>4.0.0</modelVersion>
    <parent>
        <groupId>org.springframework.boot</groupId>
        <artifactId>spring-boot-starter-parent</artifactId>
        <version>3.0.6</version>
        <relativePath/> <!-- lookup parent from repository -->
    </parent>
    <groupId>dev.fromnowon</groupId>
    <artifactId>mfi-server</artifactId>
    <version>0.0.1-SNAPSHOT</version>
    <name>mfi-server</name>
    <description>mfi-server</description>
    <properties>
        <java.version>17</java.version>
        <kotlin.version>1.9.0</kotlin.version>
    </properties>
    <dependencies>
        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter-web</artifactId>
        </dependency>
        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter-validation</artifactId>
        </dependency>
        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-configuration-processor</artifactId>
            <optional>true</optional>
        </dependency>
        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter-test</artifactId>
            <scope>test</scope>
        </dependency>
        <dependency>
            <groupId>org.springframework.retry</groupId>
            <artifactId>spring-retry</artifactId>
        </dependency>
        <dependency>
            <groupId>org.springframework</groupId>
            <artifactId>spring-aspects</artifactId>
        </dependency>
        <dependency>
            <groupId>org.projectlombok</groupId>
            <artifactId>lombok</artifactId>
            <optional>true</optional>
        </dependency>
        <dependency>
            <groupId>com.fasterxml.jackson.dataformat</groupId>
            <artifactId>jackson-dataformat-csv</artifactId>
        </dependency>
        <dependency>
            <scope>compile</scope>
            <groupId>org.apache.poi</groupId>
            <artifactId>poi-ooxml</artifactId>
            <version>5.2.2</version>
        </dependency>
        <dependency>
            <groupId>org.jetbrains.kotlin</groupId>
            <artifactId>kotlin-stdlib</artifactId>
            <version>${kotlin.version}</version>
        </dependency>
        <dependency>
            <groupId>org.jetbrains.kotlin</groupId>
            <artifactId>kotlin-reflect</artifactId>
            <version>${kotlin.version}</version>
        </dependency>
        <dependency>
            <groupId>com.fasterxml.jackson.module</groupId>
            <artifactId>jackson-module-kotlin</artifactId>
        </dependency>
    </dependencies>

    <build>
        <plugins>
            <plugin>
                <groupId>org.springframework.boot</groupId>
                <artifactId>spring-boot-maven-plugin</artifactId>
                <configuration>
                    <excludes>
                        <exclude>
                            <groupId>org.projectlombok</groupId>
                            <artifactId>lombok</artifactId>
                        </exclude>
                    </excludes>
                </configuration>
            </plugin>
            <plugin>
                <groupId>org.jetbrains.kotlin</groupId>
                <artifactId>kotlin-maven-plugin</artifactId>
                <version>${kotlin.version}</version>
                <extensions>true</extensions> <!-- You can set this option
            to automatically take information about lifecycles -->
                <executions>
                    <execution>
                        <id>compile</id>
                        <goals>
                            <goal>compile</goal> <!-- You can skip the <goals> element
                        if you enable extensions for the plugin -->
                        </goals>
                        <configuration>
                            <sourceDirs>
                                <sourceDir>${project.basedir}/src/main/kotlin</sourceDir>
                                <sourceDir>${project.basedir}/src/main/java</sourceDir>
                            </sourceDirs>
                        </configuration>
                    </execution>
                    <execution>
                        <id>test-compile</id>
                        <goals>
                            <goal>test-compile</goal>
                        </goals> <!-- You can skip the <goals> element
                    if you enable extensions for the plugin -->
                        <configuration>
                            <sourceDirs>
                                <sourceDir>${project.basedir}/src/test/kotlin</sourceDir>
                                <sourceDir>${project.basedir}/src/test/java</sourceDir>
                            </sourceDirs>
                        </configuration>
                    </execution>
                </executions>
                <configuration>
                    <compilerPlugins>
                        <!-- Or "spring" for the Spring support -->
                        <plugin>all-open</plugin>

                        <!-- Or "jpa" for JPA support -->
                        <plugin>no-arg</plugin>
                    </compilerPlugins>

                    <pluginOptions>
                        <!-- Each annotation is placed on its own line -->
                        <option>all-open:annotation=com.my.Annotation</option>
                        <option>all-open:annotation=com.their.AnotherAnnotation</option>

                        <option>no-arg:annotation=com.my.Annotation</option>
                        <!-- Call instance initializers in the synthetic constructor -->
                        <!-- <option>no-arg:invokeInitializers=true</option> -->
                    </pluginOptions>
                </configuration>
                <dependencies>
                    <dependency>
                        <groupId>org.jetbrains.kotlin</groupId>
                        <artifactId>kotlin-maven-allopen</artifactId>
                        <version>${kotlin.version}</version>
                    </dependency>
                    <dependency>
                        <groupId>org.jetbrains.kotlin</groupId>
                        <artifactId>kotlin-maven-noarg</artifactId>
                        <version>${kotlin.version}</version>
                    </dependency>
                </dependencies>
            </plugin>
            <plugin>
                <groupId>org.apache.maven.plugins</groupId>
                <artifactId>maven-compiler-plugin</artifactId>
                <version>3.5.1</version>
                <executions>
                    <!-- Replacing default-compile as it is treated specially by Maven -->
                    <execution>
                        <id>default-compile</id>
                        <phase>none</phase>
                    </execution>
                    <!-- Replacing default-testCompile as it is treated specially by Maven -->
                    <execution>
                        <id>default-testCompile</id>
                        <phase>none</phase>
                    </execution>
                    <execution>
                        <id>java-compile</id>
                        <phase>compile</phase>
                        <goals>
                            <goal>compile</goal>
                        </goals>
                    </execution>
                    <execution>
                        <id>java-test-compile</id>
                        <phase>test-compile</phase>
                        <goals>
                            <goal>testCompile</goal>
                        </goals>
                    </execution>
                </executions>
            </plugin>
        </plugins>
    </build>

</project>

代码差异如图:

源代码目录

其实我是更偏向于 src/main/java 和 src/main/kotlin各自分开，也就是 src/main/java 中只用Java语言写，src/main/kotlin 中只用 kotlin 写。

所以让我们建立 kotlin 源代码目录，把软件包搞一下，建个最简单的 kotlin 类试一下:

结尾

其实这里只是一个demo，实际应用中还有很多问题需要去解决。
比如 annotationProcessor,需要使用 kapt,如果只有一种语言的话比较简单，如果是Java、kotlin混编的话，就需要调试配置 annotationProcessor。
还有一些经典的互调用的问题，典型的举个例子，就是做参数校验的时候，在Java类中，可以直接在属性上使用 @NotBlank 等等,但在 Kotlin 中，会发现直接写是不起作用的，需要使用 @get:NotBlank 或者 @field:NotBlank

在后续的文章中，看看把这些坑尽可能的说一下.

因为刚刚接触不久，所以有些东西理解不到根本。如果发现写的有问题还请指出. 感谢阅读:)