利用注解进行sql反射代码示例

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

表名注解

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

字段注解

 @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;
     }
 }

一个表单类

 @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;
     }

 }

另一个表单类

 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();

     }
 }

测试类

 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

输出结果