注解（二）模拟实体到数据库表字段的映射

package com.ann.test;

import java.lang.annotation.Documented;
import java.lang.annotation.ElementType;
import java.lang.annotation.Inherited;
import java.lang.annotation.Retention;
import java.lang.annotation.RetentionPolicy;
import java.lang.annotation.Target;
/**
 * 字段自定义注解
 */
@Target({ElementType.FIELD})
@Retention(RetentionPolicy.RUNTIME)
@Inherited
@Documented
public @interface Column {

    String value();
}

package com.ann.test;

import java.lang.annotation.Documented;
import java.lang.annotation.ElementType;
import java.lang.annotation.Inherited;
import java.lang.annotation.Retention;
import java.lang.annotation.RetentionPolicy;
import java.lang.annotation.Target;
/**
 * 表自定义注解
 */
@Target({ElementType.TYPE})
@Retention(RetentionPolicy.RUNTIME)
@Inherited
@Documented
public @interface Table {

    String value();
}

package com.ann.test;
/**
 * 用户实体使用注解
 */
@Table("user")
public class User {
    
    @Column("id")
    private int id;
    
    @Column("userName")
    private String userName;
    
    @Column("sex")
    private int sex;
    
    @Column("mobile")
    private String mobile;

    public int getId() {
        return id;
    }

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

    public String getUserName() {
        return userName;
    }

    public void setUserName(String userName) {
        this.userName = userName;
    }

    public int getSex() {
        return sex;
    }

    public void setSex(int sex) {
        this.sex = sex;
    }


    public String getMobile() {
        return mobile;
    }

    public void setMobile(String mobile) {
        this.mobile = mobile;
    }
    

}

package com.ann.test;
import java.lang.reflect.Field;
import java.lang.reflect.Method;
/**
 * 模拟实体到数据库表字段的测试
 */
public class Test {

    public static void main(String[] args) {
        User u = new User();
        u.setUserName("张三");
        u.setSex(1);
        System.out.println(parseUser(u));
    }
    
    public static String parseUser(User u){
        StringBuffer sb = new StringBuffer();
        sb.append("select * from ");
        try {
            //1.1使用类加载器加载类, 获取表名
            Class c = Class.forName("com.ann.test.User");
            //1.2找到类上的注解，并拿到注解实例
            if(c.isAnnotationPresent(Table.class)){
                Table t = (Table)c.getAnnotation(Table.class);
                String tableName = t.value();
                sb.append(tableName);
            }
            sb.append(" where 1=1");
            //2.获取字段名与值
            Field[] fs = c.getDeclaredFields();
            for(Field f : fs){
                //2.1字段名
                String column = "";
                if(f.isAnnotationPresent(Column.class)){
                    Column fld = (Column)f.getAnnotation(Column.class);
                    column = fld.value();
                }
                //2.2字段值
                String fieldName = f.getName();
                String getMethod = "get"+fieldName.substring(0, 1).toUpperCase()+fieldName.substring(1);
                Method method = c.getMethod(getMethod);
                Object fieldValue = method.invoke(u);
                if(fieldValue instanceof Integer && (Integer)fieldValue == 0){
                    continue;
                }
                if(fieldValue != null){
                    sb.append(" and ").append(column).append("=");
                    if(fieldValue instanceof String){
                        sb.append("'").append(fieldValue).append("'");
                    }else{
                        sb.append(fieldValue);
                    }
                }
            }
            
        } catch (Exception e) {
            e.printStackTrace();
        }
        return sb.toString();
    }
}

 输出结果：

select * from user where 1=1 and userName='张三' and sex=1