java反射获取注解并拼接sql语句

先建两个注解 分别为 Table 和 Column

package com.hk.test;

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

@Target({ElementType.TYPE})
@Retention(RetentionPolicy.RUNTIME)
public @interface Table {
    String value();
}

package com.hk.test;

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

@Target({ElementType.FIELD})
@Retention(RetentionPolicy.RUNTIME)
public @interface Column {
    String value();
}

然后新建一个 bean 类 Filter.java （本类可根据自己需求更改，只要样式不变就好）

package com.hk.test;
@Table("user")
public class Filter {
    @Column("id")
    private int id;
    @Column("user_name")
    private String userName;
    @Column("age")
    private int age;
    @Column("email")
    private String email;
    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 getAge() {
        return age;
    }
    public void setAge(int age) {
        this.age = age;
    }
    public String getEmail() {
        return email;
    }
    public void setEmail(String email) {
        this.email = email;
    }

}

然后测试类

package com.hk.test;

import java.lang.reflect.Field;
import java.lang.reflect.Method;
/**
 *
 * @author hk_z
 * @deprecated 对类进行反射 获取注解和字段名 拼接成sql语句
 * @version 0.1
 */
public class Test {
    public static void main(String[] args) {
        Filter f1 = new Filter();
        f1.setId(10);

        Filter f2 = new Filter();
        f2.setUserName("lucy"); //模糊查询

        Filter f3 = new Filter();
        f3.setEmail("[email protected],[email protected]"); //任意其一

        String sql1 =query(f1);
        System.out.println(sql1);
        String sql2 =query(f2);
        System.out.println(sql2);
        String sql3 =query(f3);
        System.out.println(sql3);
    }

    private static String query(Filter f1) {
        // TODO Auto-generated method stub
        StringBuilder sb =new StringBuilder();
        //1.获取到class
        Class c = f1.getClass();
        //2.获取到table 的名字
        boolean exists = c.isAnnotationPresent(Table.class); //class 中有没有table的注解
        if(!exists){
            return null;
        }
        Table t= (Table)c.getAnnotation(Table.class);
        String tableName = t.value(); //表名
        sb.append("select * from ").append(tableName).append(" where 1 = 1");
        //3.遍历所有的字段
        Field[] fArray = c.getDeclaredFields();
        for(Field field:fArray){
            //4.处理每个字段对应的sql
            //4.1 拿到字段名
            boolean fExists = field.isAnnotationPresent(Column.class);
            if(!fExists){
                continue;
            }
            Column column = field.getAnnotation(Column.class);
            String columnName = column.value();  //表里面字段的名字
            //4.2拿到字段的值
            String filedName = field.getName(); //变量的名字
            String getMethodName = "get"+filedName.substring(0,1).toUpperCase()+filedName.substring(1);
            Object fieldValue = null;
            //拼装get方法 获取返回值 ；
            try {
                Method getMethod = c.getMethod(getMethodName); //反射
                fieldValue = getMethod.invoke(f1);     //反射调用    

            } catch (Exception e) {
                // TODO Auto-generated catch block
                e.printStackTrace();
            }
            //4.3 拼装sql
            if(fieldValue == null||(fieldValue instanceof Integer &&(Integer)fieldValue==0))
            {
                continue;
            }
            sb.append(" and ").append(filedName);
            String [] val=null;
            if(fieldValue instanceof String){ //字串型并且有逗号 进行拆分
                if(((String)fieldValue).contains(",")){
                    val = ((String) fieldValue).split(",");
                    sb.append(" in(");
                    for(String v:val){
                        sb.append("‘").append(v).append("‘").append(",");
                    }
                    sb.deleteCharAt(sb.length()-1);
                    sb.append(")");
                    }
                else{
                    sb.append(" = ").append("‘").append(fieldValue).append("‘");
                }
            }
            else if(fieldValue instanceof Integer){
            sb.append(" = ").append(fieldValue);
            }

        }
        return sb.toString();
    }
}