利用注解进行sql反射代码示例

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

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

@Table("user")
public class Filter {
    @Column("id")
    private int id;
    @Column("username")
    private String userName;
    @Column("nickname")
    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;
    }
}

@Table("deapartment")
public class Filter2 {
    @Column("id")
    private int id;
    @Column("name")
    private String name;
    @Column("amount")
    private String amount;
    @Column("age")
    private int age;
    @Column("city")
    private String city;
    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 getAmount() {
        return amount;
    }
    public void setAmount(String amount) {
        this.amount = amount;
    }
    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 class Test {
    public static void main(String[] args) {
        Filter f1 = new Filter();
        f1.setId(10);
        Filter f2 = new Filter();
        f2.setAge(45);
        f2.setCity("china");
        f2.setUserName("lucy");
        Filter f3 = new Filter();
        f3.setEmail("liu@sh.com,dahod@1223.com");
        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.setId(02);
        filter2.setAge(15);
        filter2.setAmount("14");
        filter2.setName("小明");    
        System.out.println(query(filter2));
    }
    @SuppressWarnings("unused")
    private static String query(Object f){
        StringBuffer sb = new StringBuffer();
        //1.获取到class
        Class c = f.getClass();
        //2.获取到table的名字
        boolean exsits = c.isAnnotationPresent(Table.class);
        if(!exsits){
            return null;
        }
        Table t = (Table) c.getAnnotation(Table.class);
        String tableName = t.value();
        sb.append("select *from ").append(tableName).append(" where 1=1");
        //3.变量所有的字段
        Field[] farray = c.getDeclaredFields();
        for(Field field :farray){
            //4.0处理每个字段对应的名字
            //4.1拿到字段名
            boolean fExist = field.isAnnotationPresent(Column.class);
            if(!fExist){
                continue;
            }
            Column column = field.getAnnotation(Column.class);
            String coiumnName = column.value();
            //4.2拿到字段的值
            String filedName = field.getName();
            String getMethodName = "get"+filedName.substring(0,1).toUpperCase()+filedName.substring(1);
            Object fieldValue = null;
            try {
                Method getMethod = c.getMethod(getMethodName);
                fieldValue =getMethod.invoke(f);
            } 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);
            if(fieldValue instanceof String){
                if(((String)fieldValue).contains(",")){
                    String [] values = ((String)fieldValue).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(fieldValue).append("'");
                }
            }else if(fieldValue instanceof Integer){
                sb.append("=").append(fieldValue);
            }
            //sb.append(" and ").append(filedName).append("=").append(fieldValue);
        }
        return sb.toString();
        
        
    }
}

select *from user where 1=1 and id=10
select *from user where 1=1 and userName='lucy' and age=45 and city='china'
select *from user where 1=1 and email in('liu@sh.com','dahod@1223.com')
select *from deapartment where 1=1 and id=2 and name='小明' and amount='14' and age=15