首先新建2个注解类

package cc.openkit.kitTest;

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 cc.openkit.kitTest;

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();
}

对象类

package cc.openkit.kitTest;

@Table("user")
public class Filter {
@Column("id")
private int id;

@Column("user_name")
private String userName;

@Column("nick_name")
private String nickName;

@Column("age")
private int age;

@Column("city")
private String city;

@Column("email")
private String email;

@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 String getNickName() {
return nickName;
}

public void setNickName(String nickName) {
this.nickName = nickName;
}

public int getAge() {
return age;
}

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

public String getCity() {
return city;
}

public void setCity(String city) {
this.city = city;
}

public String getEmail() {
return email;
}

public void setEmail(String email) {
this.email = email;
}

public String getMobile() {
return mobile;
}

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

获取注解

package cc.openkit.kitTest;

import java.lang.annotation.Annotation;
import java.lang.reflect.Field;
import java.lang.reflect.Method;

public class Test {
    public static void main(String[] args) {
        Filter f1 = new Filter();
        f1.setId(10);// 查询id为10的用户

        Filter f2 = new Filter();
        f1.setUserName("lucy");// 根据用户查询

        Filter f3 = new Filter();
        f1.setEmail("liu@sina.com,zh@163.com,222@qq.com");// 查询邮箱为其中任意一个的用户

        String sql1 = query(f1);
        String sql2 = query(f2);
        String sql3 = query(f3);

        System.out.println(sql1);
        System.out.println(sql2);
        System.out.println(sql3);

        Filter2 filter2 = new Filter2();
        filter2.setName("你好");
        System.out.println(query(filter2));
    }

    private static String query(Object f) {

        StringBuffer sb = new StringBuffer();
        // 1. 获取到Class
        Class c = f.getClass();
        // 2. 获取table的名字
        boolean exists = c.isAnnotationPresent(Table.class); // 判断传来的是不是Table对象
        if(!exists){
            return null;
        }
        Table t = (Table) c.getAnnotation(Table.class);
        String tableName = t.value();
        sb.append("select * from ").append(tableName).append(" where 1=1");

        // 遍历所有的字段
        Field[] fArray = c.getDeclaredFields();
        for(Field field : fArray){
            // 4. 处理每一个字段对应的sql
            // 4.1. 拿到字段名
            boolean fExists = field.isAnnotationPresent(Column.class);
            // 如果不存在不需要处理
           if(!fExists){
               continue;
           }
           // 否则去除值
           Column column = field.getAnnotation(Column.class);
           String columnName = column.value();
           // 4.2. 拿到字段的值
           // 反射调用get取出字段名
           String filedName = field.getName();
           String getMethodName = "get"+filedName.substring(0,1).toUpperCase()+filedName.substring(1);

           Object filedValue = null;
           try {
               Method getMethod = c.getMethod(getMethodName);
               filedValue = getMethod.invoke(f); 
           } catch (Exception e) {
               e.printStackTrace();
           }

           // 4.3. 拼接sql
           if(filedValue==null ||
               (filedValue instanceof Integer && (Integer)filedValue==0)){
               // 判断如果是 String 类型 == null，或者Int 类型==0，就不做处理
               continue;
           }
           sb.append(" and ").append(filedName);
           if(filedValue instanceof String){
               // 如果email
               if(((String) filedValue).contains(",")){
                   String[] values = ((String) filedValue).split(",");
                   sb.append(" in(");
                   for(String v:values){
                   sb.append("'").append(v).append("'").append(",");
               }
               sb.deleteCharAt(sb.length()-1);
               sb.append(")");
            }else{
               sb.append("=").append("'").append(filedValue).append("'");
            }
        }else if(filedValue instanceof Integer){
            sb.append("=").append(filedValue);
        }
    }
        return String.valueOf(sb);
    }
}