定义描述用户表的注解：

package dao;import java.lang.annotation.ElementType;import java.lang.annotation.Retention;import java.lang.annotation.RetentionPolicy;import java.lang.annotation.Target;// 作用域@Target({ ElementType.TYPE })@Retention(RetentionPolicy.RUNTIME)public @interface Table {    String value();}

 定义描述用户属性的注解：

1 package dao; 2  3 import java.lang.annotation.ElementType; 4 import java.lang.annotation.Retention; 5 import java.lang.annotation.RetentionPolicy; 6 import java.lang.annotation.Target; 7 13 // 作用域14 @Target({ ElementType.FIELD })15 @Retention(RetentionPolicy.RUNTIME)16 public @interface Column {17     String value();18 }

定义映射Bean类User：

1 package dao; 2  3 /** 4  *  5  * 用户表，字段包括：用户ID、用户名、昵称、年龄、性别、所在城市、邮箱、手机号： 6  *  7  * @author 8  */ 9 @Table("user")10 public class User {11     @Column("id")12     private int id;13 14     @Column("user_name")15     private String userName;16 17     @Column("nick_name")18     private String nickName;19 20     @Column("age")21     private int age;22 23     @Column("city")24     private String city;25 26     @Column("email")27     private String email;28 29     @Column("mobile")30     private String mobile;31 32     public int getId() {33         return id;34     }35 36     public void setId(int id) {37         this.id = id;38     }39 40     public String getUserName() {41         return userName;42     }43 44     public void setUserName(String userName) {45         this.userName = userName;46     }47 48     public String getNickName() {49         return nickName;50     }51 52     public void setNickName(String nickName) {53         this.nickName = nickName;54     }55 56     public int getAge() {57         return age;58     }59 60     public void setAge(int age) {61         this.age = age;62     }63 64     public String getCity() {65         return city;66     }67 68     public void setCity(String city) {69         this.city = city;70     }71 72     public String getEmail() {73         return email;74     }75 76     public void setEmail(String email) {77         this.email = email;78     }79 80     public String getMobile() {81         return mobile;82     }83 84     public void setMobile(String mobile) {85         this.mobile = mobile;86     }87 }

根据参数动态返回查询语句：

1 package dao; 2  3 import java.lang.reflect.Field; 4 import java.lang.reflect.Method; 5  6 /** 7  * 根据参数动态返回查询语句 8  *  9  * @author10  */11 public class ReturnQuery {12 13     public static String query(User u1) {14         StringBuilder str = new StringBuilder();15         // 1.获取一个类class16         Class c = u1.getClass();17         // 2.获取Table的名字18         boolean exists = c.isAnnotationPresent(Table.class);19         if (!exists) {20             return null;21         }22         Table t = (Table) c.getAnnotation(Table.class);23         String tableName = t.value();24         str.append("select * from ").append(tableName).append("where 1=1");25         // 3.遍历所有的 字段26         Field fArray[] = c.getDeclaredFields();27         for (Field field : fArray) {28             // 4.处理每个字段对应的sql29             // 4.1取到字段名30             boolean fExists = field.isAnnotationPresent(Column.class);// 判断是否包含Column类型的注解31             if (!fExists) {32                 continue;33             }34             Column column = field.getAnnotation(Column.class);35             String columnName = column.value();36             // 4.2取到字段的值37             String fieldName = field.getName();38             // 获取相应字段的getXXX()方法39             String getMethodName = "get" + fieldName.substring(0, 1).toUpperCase() + fieldName.substring(1);40             Object fieldValue=null;41             try {42                 Method getMethod = c.getMethod(getMethodName);43                 fieldValue = getMethod.invoke(u1);44             } catch (Exception e) {45                 e.printStackTrace();46             }47             //4.3拼接Sql48             if (fieldValue==null||fieldValue instanceof Integer &&(Integer)fieldValue==0) {49                 continue;50             }51             str.append(" and ").append(fieldName);52             if (fieldValue instanceof String) {53                 if (((String) fieldValue).contains(",")) {54                     String[] values=((String) fieldValue).split(",");55                     str.append(" in (");56                     for (String s : values) {57                         str.append("'").append(s).append("'").append(",");58                     }59                     str.deleteCharAt(str.length()-1);60                     str.append(")");61                 }else{62                     str.append("=").append("'").append(fieldValue).append("' ");63                 }64             }else {65                 str.append("=").append(fieldValue);66             }67         }68         return str.toString();69     }70 71 }

测试类：

1 package dao; 2  3 public class Test { 4     public static void main(String[] args) { 5         User u1 = new User(); 6         u1.setId(10); // 查询id 7  8         User u2 = new User(); 9         u2.setUserName("JSFei"); // 模糊查询用户名10         u2.setAge(21);11 12         User u3 = new User();13         u3.setEmail("123@163.com,123@qq.com"); // 查询邮箱有任意一个的用户14         15         String sql1 = ReturnQuery.query(u1);    16         String sql2 = ReturnQuery.query(u2);    17         String sql3 = ReturnQuery.query(u3);18           19         System.out.println(sql1);  20         System.out.println(sql2);  21         System.out.println(sql3);  22     }23 }

输出结果：

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