spring boot 之使用mapstruct

　　最近在阅读swagger源码，当看到 springfox.documentation.swagger2.mappers.ModelMapper 类时，无意中看到该类上面使用的 org.mapstruct.Mapper 注解时，对这个注解一时竟想不出个所意然来。便打开百度搜索了一番，有关这个注解的文章不是很多，从这些文章中了解到，这个注解跟JSR 269 有关，下面列出这个注解相关的文章链接。

---

 相关的文章链接：

1. mapstruct官网 http://mapstruct.org/
2. mapstruct github网址：https://github.com/mapstruct/mapstruct
3. JSR 269: Pluggable Annotation Processing API  https://jcp.org/en/jsr/detail?id=269
4. 插入式注解处理API(Pluggable Annotation Processing API)  https://blog.csdn.net/yczz/article/details/34116189
5. MapStruct实体间转换快速入门  https://blog.csdn.net/lx_yoyo/article/details/75061614

　　当看完上面的几篇的文章之后，对这个注解到底起何作用，仍然是一知半解。于是参照上面列表中的 MapStruct实体间转换快速入门 ，当我把工程建好，copy完相关的代码之后，根据文章的提示，执行mvn install（mvn compile）命令之后，没有出现文章中提到的在 target\generated-sources\annotations 会自动生成PeopleMapperImpl.Java 源文件，反到是控制台打印出的日志信息提示编译失败，错误信息如下所示：

[INFO] -------------------------------------------------------------
[ERROR] COMPILATION ERROR :
[INFO] -------------------------------------------------------------
[ERROR] /F:/java.ws.01/springboot-example/example4/src/main/java/com/github/torlight/sbex/PeopleMapper.java:[21,15] No property named "age" exists in source parameter(s). Did you mean "null"?
[ERROR] /F:/java.ws.01/springboot-example/example4/src/main/java/com/github/torlight/sbex/PeopleMapper.java:[32,10] No property named "user.name" exists in source parameter(s). Did you mean "null"?
[INFO] 2 errors
[INFO] -------------------------------------------------------------
[INFO] ------------------------------------------------------------------------
[INFO] BUILD FAILURE
[INFO] ------------------------------------------------------------------------
[INFO] Total time: 5.951 s
[INFO] Finished at: 2018-08-19T10:52:59+08:00
[INFO] Final Memory: 26M/282M
[INFO] ------------------------------------------------------------------------
[ERROR] Failed to execute goal org.apache.maven.plugins:maven-compiler-plugin:3.5.1:compile (default-compile) on project example4: Compilation failure: Compilation failure:
[ERROR] /F:/java.ws.01/springboot-example/example4/src/main/java/com/github/torlight/sbex/PeopleMapper.java:[21,15] No property named "age" exists in source parameter(s). Did you mean "null"?
[ERROR] /F:/java.ws.01/springboot-example/example4/src/main/java/com/github/torlight/sbex/PeopleMapper.java:[32,10] No property named "user.name" exists in source parameter(s). Did you mean "null"?
[ERROR] -> [Help 1]
org.apache.maven.lifecycle.LifecycleExecutionException: Failed to execute goal org.apache.maven.plugins:maven-compiler-plugin:3.5.1:compile (default-compile) on project example4: Compilation failure
    at org.apache.maven.lifecycle.internal.MojoExecutor.execute(MojoExecutor.java:212)
    at org.apache.maven.lifecycle.internal.MojoExecutor.execute(MojoExecutor.java:153)
    at org.apache.maven.lifecycle.internal.MojoExecutor.execute(MojoExecutor.java:145)
    at org.apache.maven.lifecycle.internal.LifecycleModuleBuilder.buildProject(LifecycleModuleBuilder.java:116)
    at org.apache.maven.lifecycle.internal.LifecycleModuleBuilder.buildProject(LifecycleModuleBuilder.java:80)
    at org.apache.maven.lifecycle.internal.builder.singlethreaded.SingleThreadedBuilder.build(SingleThreadedBuilder.java:51)
    at org.apache.maven.lifecycle.internal.LifecycleStarter.execute(LifecycleStarter.java:128)
    at org.apache.maven.DefaultMaven.doExecute(DefaultMaven.java:307)
    at org.apache.maven.DefaultMaven.doExecute(DefaultMaven.java:193)
    at org.apache.maven.DefaultMaven.execute(DefaultMaven.java:106)
    at org.apache.maven.cli.MavenCli.execute(MavenCli.java:862)
    at org.apache.maven.cli.MavenCli.doMain(MavenCli.java:286)
    at org.apache.maven.cli.MavenCli.main(MavenCli.java:197)
    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.codehaus.plexus.classworlds.launcher.Launcher.launchEnhanced(Launcher.java:289)
    at org.codehaus.plexus.classworlds.launcher.Launcher.launch(Launcher.java:229)
    at org.codehaus.plexus.classworlds.launcher.Launcher.mainWithExitCode(Launcher.java:415)
    at org.codehaus.plexus.classworlds.launcher.Launcher.main(Launcher.java:356)
Caused by: org.apache.maven.plugin.compiler.CompilationFailureException: Compilation failure
    at org.apache.maven.plugin.compiler.AbstractCompilerMojo.execute(AbstractCompilerMojo.java:972)
    at org.apache.maven.plugin.compiler.CompilerMojo.execute(CompilerMojo.java:129)
    at org.apache.maven.plugin.DefaultBuildPluginManager.executeMojo(DefaultBuildPluginManager.java:134)
    at org.apache.maven.lifecycle.internal.MojoExecutor.execute(MojoExecutor.java:208)
    ... 20 more
[ERROR]
[ERROR]
[ERROR] For more information about the errors and possible solutions, please read the following articles:
[ERROR] [Help 1] http://cwiki.apache.org/confluence/display/MAVEN/MojoFailureException

　　当出现上面的错误之后，先是在网上找了一下，但没有找到相关的资料，没办法只能靠自己解决了。查看工程的pom.xml文件，有用到maven-compiler-plugin 插件，看到该插件的配置项中mapstruct-processor ，心里也清楚当maven执行maven-compiler-plugin 插件中相关类的方法时，肯定会执行mapstruct-processor 中相关类的方法。可是不清楚具体会先从那个类的方法开始执行。

　　没办法，只能根据上面的异常提示信息，在maven源码工程中一路跟踪下来，发现错误源是当执行SourceReference类的getSourceEntries方法时触发的。No property named "age" exists in source parameter(s). Did you mean "null"?  在被转换的实体中找不到age属性，可是在PeopleEntity 实体中本来就存在age属性。原来报错是因为getSourceEntries方法是通过反射读取实体的get方法来获取属性，然后再进行属性比较，怪不得会报错。当找到报错的原因之后，我把目光停留在源码中的注释 //constructor, getters, setters etc.  原来实体中的getter，setter 方法都被省略了。

 package com.github.torlight.sbex;

 public class PeopleEntity {
     private Integer age;
     private String name;
     private String callNumber;
     private String address;
     private String email;

     public PeopleEntity() {

     }

     public PeopleEntity(Integer age, String name, String callNumber, String address, String email) {
         this.age = age;
         this.name = name;
         this.callNumber = callNumber;
         this.address = address;
         this.email = email;
     }

 　　//constructor, getters, setters etc.

 }

---

修改之后的代码：

 package com.github.torlight.sbex;

 public class PeopleDTO {

     private String phoneNumber;
     private String address;
     private String email;
     private User  user;

     public PeopleDTO() {

     }

     public PeopleDTO(String phoneNumber, String address, String email, User user) {
         this.phoneNumber = phoneNumber;
         this.address = address;
         this.email = email;
         this.user = user;
     }

     public String getPhoneNumber() {
         return phoneNumber;
     }

     public void setPhoneNumber(String phoneNumber) {
         this.phoneNumber = phoneNumber;
     }

     public String getAddress() {
         return address;
     }

     public void setAddress(String address) {
         this.address = address;
     }

     public String getEmail() {
         return email;
     }

     public void setEmail(String email) {
         this.email = email;
     }

     public User getUser() {
         return user;
     }

     public void setUser(User user) {
         this.user = user;
     }

 }

 package com.github.torlight.sbex;

 public class PeopleEntity {
     private Integer age;
     private String name;
     private String callNumber;
     private String address;
     private String email;

     public PeopleEntity() {

     }

     public PeopleEntity(Integer age, String name, String callNumber, String address, String email) {
         this.age = age;
         this.name = name;
         this.callNumber = callNumber;
         this.address = address;
         this.email = email;
     }

     public Integer getAge() {
         return age;
     }

     public void setAge(Integer age) {
         this.age = age;
     }

     public String getName() {
         return name;
     }

     public void setName(String name) {
         this.name = name;
     }

     public String getCallNumber() {
         return callNumber;
     }

     public void setCallNumber(String callNumber) {
         this.callNumber = callNumber;
     }

     public String getAddress() {
         return address;
     }

     public void setAddress(String address) {
         this.address = address;
     }

     public String getEmail() {
         return email;
     }

     public void setEmail(String email) {
         this.email = email;
     }

 }   

package com.github.torlight.sbex;

public class User {
    private Integer age;
    private String name;

    public User() {

    }

    public User(Integer age, String name) {
        this.age = age;
        this.name = name;
    }

    public Integer getAge() {
        return age;
    }

    public void setAge(Integer age) {
        this.age = age;
    }

    public String getName() {
        return name;
    }

    public void setName(String name) {
        this.name = name;
    }
}

　　

---

　　执行mvn install（mvn compile）命令之后，控制台没有提示报错，但在 \target\generated-sources\annotations\ 文件夹下面还是空的，奇怪了？ 先执行mvn clean 然后再执行 mvn install（mvn compile）之后，终于出现了PeopleMapperImpl.java 源文件。要确保 target\class 文件夹下面为空时，执行mvn install（mvn compile）命令才能生成java源文件。

---

示例代码： https://github.com/gittorlight/springboot-example/tree/master/example4