代码链接：codegen-maven-plugin
在使用MyBatis时，需要根据库表结构编写一些通用的Mapper interface、XML、Entity，这些重复操作可以通过代码生成器自动生成，大大提高开发效率。
目前，代码生成分为两种方式：
- 模版引擎：如
velocity - 代码直接生成：如
javapoet
本文使用 javapoet直接生成Java代码，使用jdom2生成XML文件。
Maven 插件
自定义Maven插件
可参考Plugin Developers Centre
Maven内置以下3个生命周期，每个生命周期（Lifecycle）有一个或多个阶段（Phase），每个阶段可以注册多个Plugin。
- default : handles your project deployment
- clean : handles project cleaning
- site : handles the creation of your project’s web site
其中，default生成周期常用，包含以下阶段，按顺序执行：
validate- validate the project is correct and all necessary information is availablecompile- compile the source code of the projecttest- test the compiled source code using a suitable unit testing framework. These tests should not require the code be packaged or deployedpackage- take the compiled code and package it in its distributable format, such as a JAR.verify- run any checks on results of integration tests to ensure quality criteria are metinstall- install the package into the local repository, for use as a dependency in other projects locallydeploy- done in the build environment, copies the final package to the remote repository for sharing with other developers and projects.
如果单独执行某个Phase，会执行改Phase之前所有的Phases。
自定义插件套路如下：
// 选定默认Phase，可在<build>中覆盖
@Mojo(name = "codegen", defaultPhase = LifecyclePhase.GENERATE_SOURCES)
public class SQLTableGenMojo extends AbstractMojo {@Parameter(defaultValue = "${project}", required = true, readonly = true)private MavenProject project;@Parameter(property = "skip", defaultValue = "false")private boolean skip;// 自定义xml项@Parameter(property = "absoluteFilePath", required = true, readonly = true)private String absoluteFilePath;@Overridepublic void execute() throws MojoExecutionException, MojoFailureException {if (skip) {getLog().info("codegen is skipped!");return;}if (StringUtils.isBlank(absoluteFilePath) || !Files.exists(Paths.get(absoluteFilePath))) {// 异常throw new MojoExecutionException("Failed to generate code: config file does not exist");}// 日志通过getLog()获取getLog().info("codegen-maven-plugin for " + project.getName() + " starting!");doExecute(project.getBasedir().getAbsolutePath(),absoluteFilePath);}public void doExecute(String baseAbsoluteDir,String filePath) throws MojoExecutionException {// ...}}
javapoet生成Java源代码
javapoet通过Fluent api的方式构建代码：
ClassName criterion = ClassName.get(configProperties.getMapperInterfaceGenPkg(),"Criterion");TypeSpec criterion = TypeSpec.classBuilder("Criterion")// 加annotation(也可以使用AnnotationSpec构建).addAnnotation(Data.class)// List生成方式使用ParameterizedTypeName// private List<Criterion> criteria .addField(FieldSpec.builder(ParameterizedTypeName.get(ClassName.get(List.class),criterion),"criteria",Modifier.PRIVATE).build())// private Object value;.addField(FieldSpec.builder(Object.class, "value", Modifier.PRIVATE).build())// private boolean noValue;.addField(FieldSpec.builder(TypeName.BOOLEAN, "noValue", Modifier.PRIVATE).build())// 添加构造器.addMethod(MethodSpec.constructorBuilder().addModifiers(Modifier.PUBLIC).addParameter(ParameterSpec.builder(String.class, "condition").build()).addParameter(ParameterSpec.builder(Object.class, "value").build())// addStatement最后不加分号.addStatement("System.out.println(123);\n this(condition, value, null)").build())// private void addCriterion(String property){...}.addMethod(MethodSpec.methodBuilder("addCriterion").addModifiers(Modifier.PRIVATE).returns(TypeName.VOID).addParameter(String.class,"property")// $T表示类型占位符// $L for Literals// $S for Strings// $T for Types// $N for Names.addStatement(" if (value == null) {\n"+ " throw new $T(\"Value for condition cannot be null \");\n"+ "}\n"+ "criteria.add(new $T(condition,value));",RuntimeException.class,criterion).build())).build();
JDom2生成XML
Document xml = new Document();DocType mybatisDocType = new DocType("mapper", "-//mybatis.org//DTD Mapper 3.0//EN","http://mybatis.org/dtd/mybatis-3-mapper.dtd");xml.setDocType(mybatisDocType);Comment comment = new Comment("Auto generated by codegen-maven-plugin @author:baotingyu " + LocalDateTime.now());xml.addContent(comment);Element mapper = new Element("mapper");// <mapper namespace="xxx">mapper.setAttribute("namespace", configProperties.getMapperInterfaceGenPkg()+"."+xmlName);xml.addContent(mapper);
