使用Java注解实现拼接sql语句的功能

雨点打透心脏的1/2处 2022-07-24 05:21 1242阅读 0赞

使用到的两个注解类：

<span style="font-size:18px;">package dao;
    
    import java.lang.annotation.ElementType;
    import java.lang.annotation.Retention;
    import java.lang.annotation.RetentionPolicy;
    import java.lang.annotation.Target;
    
    /**
     * Created by raid on 2016/5/14.
     */
    @Target({ElementType.TYPE})
    @Retention(RetentionPolicy.RUNTIME)
    public @interface Table {
        String value();
    }
    </span>

package dao;
    
    import java.lang.annotation.ElementType;
    import java.lang.annotation.Retention;
    import java.lang.annotation.RetentionPolicy;
    import java.lang.annotation.Target;
    
    /**
     * Created by raid on 2016/5/14.
     */
    @Target({ElementType.FIELD})
    @Retention(RetentionPolicy.RUNTIME)
    public @interface Column {
        String value();
    }

package dao;
    
    /**
     * Created by raid on 2016/5/14.
     */
    @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;
        }
    }

demo类：

package dao;
    
    import java.lang.reflect.Field;
    import java.lang.reflect.Method;
    
    /**
     * Created by raid on 2016/5/14.
     */
    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();
            f2.setUserName("lucy");
    
            Filter f3 = new Filter();
            f3.setEmail("123@12.com,456@45.com,789@78.com");//查询邮箱为其中任意一个
    
            String sql1 = query(f1);
            String sql2 = query(f2);
            String sql3 = query(f3);
    
            System.out.println(sql1);;
            System.out.println(sql2);;
            System.out.println(sql3);;
        }
    
        private static String query(Filter f) {
            StringBuilder sb = new StringBuilder();
            //1.获取到class
            Class c = f.getClass();
            //2.获取到table的名字
            boolean exists = c.isAnnotationPresent(Table.class);
            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");
    
            //2.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 columName = column.value();
                //4.2拿到字段值
                String fieldName = field.getName();
                String getMethodName = "get" + fieldName.substring(0,1).toUpperCase() + fieldName.substring(1);
                Object fieldValue = null;
                try {
                    Method getMethod = c.getMethod(getMethodName);
                    fieldValue = getMethod.invoke(f);
                } catch (Exception e) {
                    e.printStackTrace();
                }
                //4.3拼装sql
                if (fieldValue == null || (fieldValue instanceof Integer && (Integer)fieldValue == 0)) {
                    continue;
                }
                if (fieldValue instanceof String) {
                    if (((String)fieldValue).contains(",")) {
                        String[] values = ((String)fieldValue).split(",");
                        fieldValue = " in(";
                        for (String v : values) {
                            fieldValue += "'" + v + "'" + ",";
                        }
                        fieldValue = ((String)fieldValue).substring(0, ((String) fieldValue).length()-1) + ")";
                    } else {
                        fieldValue = "'" + fieldValue + "'";
                    }
    
                }
    
                sb.append(" and ").append(fieldName).append("=").append(fieldValue);
            }
    
            return sb.toString();
        }
    
    }