java编程基础：注解(annotationprocessingtool)注解处理器利用注解解读类属性生成xml文件

import java.lang.annotation.ElementType;
import java.lang.annotation.Retention;
import java.lang.annotation.RetentionPolicy;
import java.lang.annotation.Target;

/**
 * @ClassName Presistent
 * @projectName: object1
 * @author: Zhangmingda
 * @description： 该注解用来修饰数据库一个表
 * date: 2021/5/19.
 */
@Target(ElementType.TYPE)   //只能修饰类、接口(包括注解类型)或枚举定义
@Retention(RetentionPolicy.SOURCE) //注解只保留在源代码中，编译器直接丢弃这种注解
public @interface Presistent {
    String table();
}

import java.lang.annotation.ElementType;
import java.lang.annotation.Retention;
import java.lang.annotation.RetentionPolicy;
import java.lang.annotation.Target;

/**
 * @ClassName Id
 * @projectName: object1
 * @author: Zhangmingda
 * @description： 用来修饰字段是否为ID字段，以及特征属性
 * date: 2021/5/19.
 */
@Target(ElementType.FIELD)  //只能修饰变量(属性)
@Retention(RetentionPolicy.SOURCE)  // 只保留在源代码中，编译的时候丢弃
public @interface Id {
    String column();
    String type();
    String generator();
}

import java.lang.annotation.ElementType;
import java.lang.annotation.Retention;
import java.lang.annotation.RetentionPolicy;
import java.lang.annotation.Target;

/**
 * @ClassName Property
 * @projectName: object1
 * @author: Zhangmingda
 * @description： 用来修饰普通字段性质
 * date: 2021/5/19.
 */
@Target(ElementType.FIELD) //只能修饰变量，属性
@Retention(RetentionPolicy.SOURCE) // 保留在源代码中，编译时丢弃
public @interface Property {
    String column();
    String type();
}

import javax.annotation.processing.AbstractProcessor;
import javax.annotation.processing.RoundEnvironment;
import javax.annotation.processing.SupportedAnnotationTypes;
import javax.annotation.processing.SupportedSourceVersion;
import javax.lang.model.SourceVersion;
import javax.lang.model.element.Element;
import javax.lang.model.element.ElementKind;
import javax.lang.model.element.Name;
import javax.lang.model.element.TypeElement;
import java.io.BufferedWriter;
import java.io.FileWriter;
import java.io.IOException;
import java.util.List;
import java.util.Set;

/**
 * @ClassName Apt
 * @projectName: object1
 * @author: Zhangmingda
 * @description： 注解处理工具类继承AbstractProcessor
 * date: 2021/5/19.
 */

@SupportedSourceVersion(SourceVersion.RELEASE_11) //支持的最新java版本
@SupportedAnnotationTypes({"Presistent","Property","Id"}) //可以处理的注解类型
public class Apt extends AbstractProcessor {
    /**
     * 该方法在命令行 java -processor Apt (本类类名)  User.java时会自动执行
     * @param set
     * @param roundEnvironment
     * @return
     */
    @Override
    public boolean process(Set<? extends TypeElement> set, RoundEnvironment roundEnvironment) {
        //获取Presistent注解修饰的类
        Set<? extends Element>  elements = roundEnvironment.getElementsAnnotatedWith(Presistent.class);
        //遍历被修饰的类名，注解进行处理
        for (Element element: elements){
            //获取javax.lang.model.element.Name类名
            Name className = element.getSimpleName();
            //获取注解对象
            Presistent presistent = element.getAnnotation(Presistent.class);
            /**
             * 创建我们对应的xml文件
             */
            try (BufferedWriter bw = new BufferedWriter(new FileWriter(className + "hbm.xml"))){
                System.out.println();
                //初始字符串初始化
                StringBuilder stringBuilder = new StringBuilder("<?xml version=\"1.0\"?>\n<!DOCTYPE hibernate-mapping PUBLIC\n\t\"-//Hibernate/Hibernate Mapping DTD 3.0//EN\"\n\t\"http://www.hibernate.org/dtd/hibernate-mapping-3.0.dtd\">\n");
                stringBuilder.append("<hibernate-mapping>\n");
                //表格维度数据
                stringBuilder.append("\t<class name=\"" + className + "\" table=\"" + presistent.table() + "\">\n");

                //字段维度//获取所有直接包含的元素
                List<? extends Element> fElements = element.getEnclosedElements();
                //对所有元素判断是否被对应注解修饰，所有修饰的都处理
                for (Element fElement: fElements){

                    //获取元素种类，如果判断为成员变量，做处理
                    if (fElement.getKind() == ElementKind.FIELD){

                        //获取成员变量上的注解
                        //判断否是ID注解修饰
                        Id id = fElement.getAnnotation(Id.class);
                        Property property = fElement.getAnnotation(Property.class);
                        if (id != null){
                            System.out.println(id);
                            System.out.println(fElement.getSimpleName());
                            stringBuilder.append("\t\t<id name=\"" + fElement.getSimpleName() + "\" column=\"" + id.column() + "\" type=\"" + id.type() + "\">\n");
                            stringBuilder.append("\t\t\t<generator class=\"" + id.generator() + "\"/>\n");
                            stringBuilder.append("\t\t</id>\n");
                        }
                        if (property != null){
                            System.out.println(property);
                            System.out.println(fElement.getSimpleName());
                            stringBuilder.append("\t\t<property name=\"" + fElement.getSimpleName() + "\" column=\"" + property.column() + "\" type=\"" + property.type() + "\"/>\n");
                        }
                    }
                }

                //表格维度结束
                stringBuilder.append("\t</class>\n");
                stringBuilder.append("</hibernate-mapping>");
                //写入文件
                bw.write(stringBuilder.toString());
            } catch (IOException e) {
                e.printStackTrace();
            }
        }
        return false;
    }
}

/**
 * @ClassName User
 * @projectName: object1
 * @author: Zhangmingda
 * @description： 用于生成XML文本的对象，只获取经过修饰符修饰的对象
 * date: 2021/5/19.
 */
@Presistent(table = "user")
public class User {
    @Id(column = "id", type = "int", generator = "auto")
    private int id;

    @Property(column = "name", type = "varchar")
    private String name;

    @Property(column = "age", type = "varchar")
    private String age;

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

    public int getId() {
        return id;
    }

    public void setId(int id) {
        this.id = id;
    }

    public String getName() {
        return name;
    }

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

    public String getAge() {
        return age;
    }

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

<?xml version="1.0"?>
<!DOCTYPE hibernate-mapping PUBLIC
    "-//Hibernate/Hibernate Mapping DTD 3.0//EN"
    "http://www.hibernate.org/dtd/hibernate-mapping-3.0.dtd">
<hibernate-mapping>
    <class name="User" table="user">
        <id name="id" column="id" type="int">
            <generator class="auto"/>
        </id>
        <property name="name" column="name" type="varchar"/>
        <property name="age" column="age" type="varchar"/>
    </class>
</hibernate-mapping>