【沉浸式解决问题】Caused by: java.lang.ClassNotFoundException: freemarker.template.Configuration

一、问题描述

在使用Mybatis-Plus的代码生成器时报错：

Caused by: java.lang.ClassNotFoundException: freemarker.template.Configuration

---

二、场景还原

1. MybatisPlusGenerator.java

import com.baomidou.mybatisplus.generator.FastAutoGenerator;
import com.baomidou.mybatisplus.generator.config.OutputFile;
import com.baomidou.mybatisplus.generator.engine.FreemarkerTemplateEngine;
import com.baomidou.mybatisplus.generator.model.ClassAnnotationAttributes;
import org.apache.ibatis.annotations.Mapper;

import java.util.*;

public class MybatisPlusGenerator {

    /**
     * Spring Boot项目生成全部表示例，有调整可以自己修改
     */
    public static void generator() {
        FastAutoGenerator.create("jdbc:mysql://127.0.0.1:3306/test?useUnicode=true&useSSL=false&characterEncoding=utf8","root","root")
                .globalConfig(builder -> {
                    builder.outputDir((System.getProperty("user.dir")+"/src/main/java"))
                            .disableOpenDir()
                            .author("baomidou")
                            .enableSwagger();
                })
                .packageConfig(builder -> {
                    builder.parent("com.baomidou")
                            .pathInfo(Collections.singletonMap(OutputFile.xml, System.getProperty("user.dir")+"/src/main/resources/mapper"));
                })
                .strategyConfig(builder -> {
                    builder.enableSkipView()
                            .entityBuilder().enableLombok(new ClassAnnotationAttributes("@Data","lombok.Data"))
                            .mapperBuilder().mapperAnnotation(Mapper.class);
                })
                .templateEngine(new FreemarkerTemplateEngine())
                .execute();

    }

    public static void main(String[] args) {
         generator()
    }
}

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三、原因分析

原因十分的简单，哈哈哈，就是mybaits-plus虽然引入了各模板引擎的依赖，但是设置了不传递，pom文件如下，可以看到所有的依赖都设置了<optional>true</optional>：

  <dependencies>
    <dependency>
      <groupId>com.baomidou</groupId>
      <artifactId>mybatis-plus-spring</artifactId>
      <version>3.5.12</version>
      <scope>compile</scope>
      <optional>true</optional>
    </dependency>
    <dependency>
      <groupId>org.apache.velocity</groupId>
      <artifactId>velocity-engine-core</artifactId>
      <version>2.4.1</version>
      <scope>compile</scope>
      <optional>true</optional>
    </dependency>
    <dependency>
      <groupId>org.freemarker</groupId>
      <artifactId>freemarker</artifactId>
      <version>2.3.33</version>
      <scope>compile</scope>
      <optional>true</optional>
    </dependency>
    <dependency>
      <groupId>com.ibeetl</groupId>
      <artifactId>beetl</artifactId>
      <version>3.17.0.RELEASE</version>
      <scope>compile</scope>
      <optional>true</optional>
    </dependency>
    <dependency>
      <groupId>com.jfinal</groupId>
      <artifactId>enjoy</artifactId>
      <version>5.2.2</version>
      <scope>compile</scope>
      <optional>true</optional>
    </dependency>
    <dependency>
      <groupId>io.swagger</groupId>
      <artifactId>swagger-annotations</artifactId>
      <version>1.6.14</version>
      <scope>compile</scope>
      <optional>true</optional>
    </dependency>
    <dependency>
      <groupId>io.springfox</groupId>
      <artifactId>springfox-swagger2</artifactId>
      <version>3.0.0</version>
      <scope>compile</scope>
      <optional>true</optional>
    </dependency>
    <dependency>
      <groupId>org.jetbrains.kotlin</groupId>
      <artifactId>kotlin-stdlib-jdk8</artifactId>
      <version>2.1.0</version>
      <scope>compile</scope>
      <optional>true</optional>
    </dependency>
  </dependencies>

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四、解决方案

再次显示声明freemarker的依赖就可以

		<dependency>
			<groupId>com.baomidou</groupId>
			<artifactId>mybatis-plus-generator</artifactId>
			<version>3.5.12</version>
		</dependency>
		<dependency>
			<groupId>org.freemarker</groupId>
			<artifactId>freemarker</artifactId>
			<scope>compile</scope>
		</dependency>