mapstruct的基本使用

你好呀，我是小邹。

今天给大家分享一下mapstruct的基本使用。

前言

MapStruct是一个Java注释处理器，用于生成类型安全的bean映射类。

您要做的就是定义一个映射器接口，该接口声明任何必需的映射方法。在编译期间，MapStruct将生成此接口的实现。此实现使用简单的Java方法调用在源对象和目标对象之间进行映射，即没有反射或类似内容。

与手动编写映射代码相比，MapStruct通过生成繁琐且易于出错的代码来节省时间。遵循配置方法上的约定，MapStruct使用合理的默认值，但在配置或实现特殊行为时不加理会。
与动态映射框架相比，MapStruct具有以下优点：

• 通过使用普通方法调用（settter/getter）而不是反射来快速执行

• 编译时类型安全性：只能映射相互映射的对象和属性，不能将order实体意外映射到customer DTO等。

• 如果有如下问题，编译时会抛出异常

  • 映射不完整（并非所有目标属性都被映射）
  • 映射不正确（找不到正确的映射方法或类型转换）

• 可以通过freemarker定制化开发

需求

我的个人博客评论功能初期是通过如下代码实现的：

/**
     * 发表评论
     */
    @ResponseBody
    @PostMapping(value = {"comments"})
    public void comments(HttpServletRequest request, @RequestBody @RequestParam("blogid") Integer blogId,
                         @RequestBody @RequestParam("blogUrl") String blogUrl,
                         @RequestBody @RequestParam("content") String content,
                         @RequestBody @RequestParam("nickname") String nickname,
                         @RequestBody @RequestParam("email") String email,
                         @RequestBody @RequestParam("avatar") String avatar,
                         @RequestBody @RequestParam("parentId") Integer parentId,
                         @RequestBody @RequestParam("parentName") String parentName,
                         @RequestBody @RequestParam("parentCommentId") Integer parentCommentId) throws Exception {
        String ip = IpUtils.getIpAddr(request);
        String province = IpUtils.getIpPossession(ip);
        Comments comments = new Comments();
        comments.setContent(content);
        comments.setEmail(email);
        comments.setCreateTime(new Date());
        comments.setBlogId(blogId);
        comments.setBlogUrl(blogUrl);
        comments.setProvince(province);
        comments.setIp(ip);
        comments.setUpdateTime(new Date());
        //数值越大则优先展示
        if (parentId == -1) {
            comments.setSort(1);
        } else {
            comments.setSort(Integer.parseInt(String.valueOf(System.currentTimeMillis() / 990)));
        }
        //未审核的评论默认不可见
        //暂时可见
        comments.setIsVisible(CommentStatus.VISIBLE.getStatus());
        //设置父节点id，-1为首节点
        comments.setParentId(parentId);
        comments.setParentName(parentName);
        comments.setNickname(nickname);
        comments.setAvatar(avatar);
        commentService.save(comments, parentCommentId);
}
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上面的代码有什么毛病吗？没有！

但是看起来很臃肿，实现的一点也不优雅。今天就用mapstruct改造一下代码。

代码

引入相关依赖

<dependency>
    <groupId>org.mapstructgroupId>
    <artifactId>mapstruct-jdk8artifactId>
    <version>1.2.0.CR1version>
dependency>

<dependency>
    <groupId>org.mapstructgroupId>
    <artifactId>mapstruct-processorartifactId>
    <version>1.2.0.CR1version>
dependency>
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创建CommentInfoConverter接口

package com.zou.blog.convert;

import com.zou.blog.model.domain.Comments;
import com.zou.blog.model.enums.CommentStatus;
import com.zou.blog.util.IpUtils;
import org.mapstruct.Mapper;

import javax.servlet.http.HttpServletRequest;
import java.util.Date;

/**
 * @author: 邹祥发
 * @date: 2022/9/8 13:46
 */
@Mapper(componentModel = "spring")
public interface CommentInfoConverter {
    default Comments map(HttpServletRequest request) throws Exception {
        String ip = IpUtils.getIpAddr(request);
        String province = IpUtils.getIpPossession(ip);
        Comments comments = new Comments();
        comments.setContent(request.getParameter("content"));
        comments.setEmail(request.getParameter("email"));
        comments.setCreateTime(new Date());
        comments.setBlogId(Integer.valueOf(request.getParameter("blogid")));
        comments.setBlogUrl(request.getParameter("blogUrl"));
        comments.setProvince(province);
        comments.setIp(ip);
        comments.setUpdateTime(new Date());
        int parentId = Integer.parseInt(request.getParameter("parentId"));
        //数值越大则优先展示
        if (parentId == -1) {
            comments.setSort(1);
        } else {
            comments.setSort(Integer.parseInt(String.valueOf(System.currentTimeMillis() / 990)));
        }
        //未审核的评论默认不可见
        //暂时可见
        comments.setIsVisible(CommentStatus.VISIBLE.getStatus());
        //设置父节点id，-1为首节点
        comments.setParentId(parentId);
        comments.setParentName(request.getParameter("parentName"));
        comments.setNickname(request.getParameter("nickname"));
        comments.setAvatar(request.getParameter("avatar"));

        return comments;
    }
}
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controller层（这样看起来是不是优雅多了😄）

  @Resource
  private CommentInfoConverter commentInfoConverter;		

/**
 * 发表评论
 */
 @ResponseBody
 @PostMapping(value = {"comments"})
 public void comments(HttpServletRequest request, @RequestBody @RequestParam("parentCommentId") Integer parentCommentId) throws Exception {
     Comments comments = commentInfoConverter.map(request);
     commentService.save(comments, parentCommentId);
}
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测试

启动报错：

java: Internal error in the mapping processor: java.lang.NullPointerException  	
at org.mapstruct.ap.internal.processor.DefaultVersionInformation.createManifestUrl(DefaultVersionInformation.java:182)  	
at org.mapstruct.ap.internal.processor.DefaultVersionInformation.openManifest(DefaultVersionInformation.java:153)  	
at org.mapstruct.ap.internal.processor.DefaultVersionInformation.getLibraryName(DefaultVersionInformation.java:129)  	
at org.mapstruct.ap.internal.processor.DefaultVersionInformation.getCompiler(DefaultVersionInformation.java:122)  	
at org.mapstruct.ap.internal.processor.DefaultVersionInformation.fromProcessingEnvironment(DefaultVersionInformation.java:95)  	
at org.mapstruct.ap.internal.processor.DefaultModelElementProcessorContext.<init>(DefaultModelElementProcessorContext.java:50)  
at org.mapstruct.ap.MappingProcessor.processMapperElements(MappingProcessor.java:218)  	
at org.mapstruct.ap.MappingProcessor.process(MappingProcessor.java:156)  	
at org.jetbrains.jps.javac.APIWrappers$ProcessorWrapper.process(APIWrappers.java:109)  	
at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)  	
at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)  	
at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)  	
at java.lang.reflect.Method.invoke(Method.java:498)  	
at org.jetbrains.jps.javac.APIWrappers$1.invoke(APIWrappers.java:213)  	
at org.mapstruct.ap.MappingProcessor.process(Unknown Source)  	
at com.sun.tools.javac.processing.JavacProcessingEnvironment.callProcessor(JavacProcessingEnvironment.java:794)  	
at com.sun.tools.javac.processing.JavacProcessingEnvironment.discoverAndRunProcs(JavacProcessingEnvironment.java:705)  
at com.sun.tools.javac.processing.JavacProcessingEnvironment.access$1800(JavacProcessingEnvironment.java:91)  	
at com.sun.tools.javac.processing.JavacProcessingEnvironment$Round.run(JavacProcessingEnvironment.java:1035)  	
at com.sun.tools.javac.processing.JavacProcessingEnvironment.doProcessing(JavacProcessingEnvironment.java:1176)  	
at com.sun.tools.javac.main.JavaCompiler.processAnnotations(JavaCompiler.java:1170)  	
at com.sun.tools.javac.main.JavaCompiler.compile(JavaCompiler.java:856)  	
at com.sun.tools.javac.main.Main.compile(Main.java:523)  	
at com.sun.tools.javac.api.JavacTaskImpl.doCall(JavacTaskImpl.java:129)  	
at com.sun.tools.javac.api.JavacTaskImpl.call(JavacTaskImpl.java:138)  	
at org.jetbrains.jps.javac.JavacMain.compile(JavacMain.java:231)  	
at org.jetbrains.jps.incremental.java.JavaBuilder.compileJava(JavaBuilder.java:501)  	
at org.jetbrains.jps.incremental.java.JavaBuilder.compile(JavaBuilder.java:353)  	
at org.jetbrains.jps.incremental.java.JavaBuilder.doBuild(JavaBuilder.java:277)  	
at org.jetbrains.jps.incremental.java.JavaBuilder.build(JavaBuilder.java:231)  	
at org.jetbrains.jps.incremental.IncProjectBuilder.runModuleLevelBuilders(IncProjectBuilder.java:1441)  	
at org.jetbrains.jps.incremental.IncProjectBuilder.runBuildersForChunk(IncProjectBuilder.java:1100)  	at org.jetbrains.jps.incremental.IncProjectBuilder.buildTargetsChunk(IncProjectBuilder.java:1224)  	at org.jetbrains.jps.incremental.IncProjectBuilder.buildChunkIfAffected(IncProjectBuilder.java:1066)  	at org.jetbrains.jps.incremental.IncProjectBuilder.buildChunks(IncProjectBuilder.java:832)  	at org.jetbrains.jps.incremental.IncProjectBuilder.runBuild(IncProjectBuilder.java:419)  	at org.jetbrains.jps.incremental.IncProjectBuilder.build(IncProjectBuilder.java:183)  	at org.jetbrains.jps.cmdline.BuildRunner.runBuild(BuildRunner.java:132)  	at org.jetbrains.jps.cmdline.BuildSession.runBuild(BuildSession.java:302)  	at org.jetbrains.jps.cmdline.BuildSession.run(BuildSession.java:132)  	at org.jetbrains.jps.cmdline.BuildMain$MyMessageHandler.lambda$channelRead0$0(BuildMain.java:219)  	at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1149)  	at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:624)  	at java.lang.Thread.run(Thread.java:748) 
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问题描述：

在使用MapStruct，idea2022.2版本在build项目的时候出现错误：java: Internal error in the mapping processor: java.lang.NullPointerException

解决方案：
Setting -->Build,Execution,Deployment -->Compiler -->User-local build加上参数：
-Djps.track.ap.dependencies=false

然后就可以正常启动了，评论功能的代码也正常执行。

总结

本篇文章记录了使用mapstruct改造代码的具体步骤，大家可作参考。

作为一名合格的Java工程师，不应该只局限于"功能的实现"，我们更应该追求高性能，优雅整洁的代码！