Java代码生成器的制作流程详解

${true ? 'checked': ''}

<#list fields as field>
 private ${field.fieldType} ${field.fieldName};
</#list>

<dependency>
 <groupId>org.freemarker</groupId>
 <artifactId>freemarker</artifactId>
 <version>2.3.28</version>
</dependency>

public class JavaProperties {
 // 包名
 private final String pkg;
 // 类名
 private final String entityName;
 // 属性集合 需要改写 equals hash 保证名字可不重复 类型可重复
 private final Set<Field> fields = new LinkedHashSet<>();
 // 导入类的不重复集合
 private final Set<String> imports = new LinkedHashSet<>();


 public JavaProperties(String entityName, String pkg) {
  this.entityName = entityName;
  this.pkg = pkg;
 }

 public void addField(Class<?> type, String fieldName) {
  // 处理 java.lang
  final String pattern = "java.lang";
  String fieldType = type.getName();
  if (!fieldType.startsWith(pattern)) {
   // 处理导包
   imports.add(fieldType);
  }
  Field field = new Field();
  // 处理成员属性的格式
  int i = fieldType.lastIndexOf(".");
  field.setFieldType(fieldType.substring(i + 1));
  field.setFieldName(fieldName);
  fields.add(field);
 }

 public String getPkg() {
  return pkg;
 }


 public String getEntityName() {
  return entityName;
 }


 public Set<Field> getFields() {
  return fields;
 }

 public Set<String> getImports() {
  return imports;
 }

 
 /**
  * 成员属性封装对象.
  */
 public static class Field {
  // 成员属性类型
  private String fieldType;
  // 成员属性名称
  private String fieldName;

  public String getFieldType() {
   return fieldType;
  }

  public void setFieldType(String fieldType) {
   this.fieldType = fieldType;
  }

  public String getFieldName() {
   return fieldName;
  }

  public void setFieldName(String fieldName) {
   this.fieldName = fieldName;
  }
  
  /** 
   * 一个类的成员属性 一个名称只能出现一次 
   * 我们可以通过覆写equals hash 方法 然后放入Set
   * 
   * @param o 另一个成员属性
   * @return 比较结果
   */
  @Override
  public boolean equals(Object o) {
   if (this == o) return true;
   if (o == null || getClass() != o.getClass()) return false;
   Field field = (Field) o;
   return Objects.equals(fieldName, field.fieldName);
  }

  @Override
  public int hashCode() {
   return Objects.hash(fieldType, fieldName);
  }
 }

}

package ${pkg};

<#list imports as impt>
import ${impt};
</#list>

/**
 * the ${entityName} type
 * @author felord.cn
 */
public class ${entityName} {

<#list fields as field>
 private ${field.fieldType} ${field.fieldName};
</#list>

}

/**
 * 简单的代码生成器.
 *
 * @param rootPath  maven 的 java 目录
 * @param templatePath 模板存放的文件夹
 * @param templateName 模板的名称
 * @param javaProperties 需要渲染对象的封装
 * @throws IOException  the io exception
 * @throws TemplateException the template exception
 */
public static void autoCodingJavaEntity(String rootPath,
           String templatePath,
           String templateName,
           JavaProperties javaProperties) throws IOException, TemplateException {

 // freemarker 配置
 Configuration configuration = new Configuration(Configuration.DEFAULT_INCOMPATIBLE_IMPROVEMENTS);

 configuration.setDefaultEncoding("UTF-8");
 // 指定模板的路径
 configuration.setDirectoryForTemplateLoading(new File(templatePath));
 // 根据模板名称获取路径下的模板
 Template template = configuration.getTemplate(templateName);
 // 处理路径问题
 final String ext = ".java";
 String javaName = javaProperties.getEntityName().concat(ext);
 String packageName = javaProperties.getPkg();
 
 String out = rootPath.concat(Stream.of(packageName.split("\\."))
   .collect(Collectors.joining("/", "/", "/" + javaName)));
 
  // 定义一个输出流来导出代码文件
 OutputStreamWriter outputStreamWriter = new OutputStreamWriter(new FileOutputStream(out));
  // freemarker 引擎将动态数据绑定的模板并导出为文件
 template.process(javaProperties, outputStreamWriter);

}

// 路径根据自己项目的特点调整
String rootPath = "C:\\Users\\felord\\IdeaProjects\\codegenerator\\src\\main\\java";
String packageName = "cn.felord.code";
String templatePath = "C:\\Users\\felord\\IdeaProjects\\codegenerator\\src\\main\\resources\\templates";
String templateName = "entity.ftl";


JavaProperties userEntity = new JavaProperties("UserEntity", packageName);

userEntity.addField(String.class, "username");
userEntity.addField(LocalDate.class, "birthday");
userEntity.addField(LocalDateTime.class, "addTime");
userEntity.addField(Integer.class, "gender");
userEntity.addField(Integer.class, "age");


autoCodingJavaEntity(rootPath, templatePath, templateName, userEntity);