整理了近期学习java注解的部分代码 ，借助java注解模拟Hibenernate ORM模型建立对象与sql语句的映射
Table 注解的创建
package com.imooc.test;
import java.lang.annotation.ElementType;
import java.lang.annotation.Retention;
import java.lang.annotation.RetentionPolicy;
import java.lang.annotation.Target;
import javax.lang.model.element.Element;
//用作类的注解，生命周期为运行时 一个值
@Target({ElementType.TYPE})
@Retention(RetentionPolicy.RUNTIME)
public @interface Table {
String value();
}字段 注解的创建
package com.imooc.test;
import java.lang.annotation.ElementType;
import java.lang.annotation.Retention;
import java.lang.annotation.RetentionPolicy;
import java.lang.annotation.Target;
/*
* 作用域为字段 运行时使用
* */
@Target({ElementType.FIELD})
@Retention(RetentionPolicy.RUNTIME)
public @interface Column {
String value();
}用户表（类）
package com.imooc.test;
@Table("user")
public class Filter {
@Column("id")
private int id;
@Column("user_name")
private String userName;
@Column("user_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;
}
}测试类的创建
package com.imooc.test;
@Table("Coder ")
public class Coder {
@Column("id")
private int id;
@Column("name")
private String userName;
@Column("age")
private int age;
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 int getAge() {
return age;
}
public void setAge(int age) {
this.age = age;
}
}sql语句的生成过程
package com.imooc.test;
import java.lang.reflect.Field;
import java.lang.reflect.InvocationTargetException;
import java.lang.reflect.Method;
public class Test {
public static void main(String[] args) {
// 代码如何与数据库做映射
Filter f1 = new Filter();
f1.setId(10);
Filter f2 = new Filter();
f2.setUserName("lucy");
Filter f3 = new Filter();
f3.setEmail("su@outlook.com,li@qq.com,hehe@163.com");
Coder c1 = new Coder();
c1.setUserName("ruanjianlin");
String sql1 = query(f1);
String sql2 = query(f2);
String sql3 = query(f3);
String sql4 = query(c1);
System.out.println(sql1);
System.out.println(sql2);
System.out.println(sql3);
System.out.println(sql4);
}
private static String query(Object f) {
// TODO Auto-generated method stub
StringBuilder sb = new StringBuilder();
// 1.获取Class通过类的类类型得到类的详细信息
Class c = f.getClass();
// Java Package.isAnnotationPresent()方法用法实例教程。方法返回true，如果指定类型的注释存在于此元素上,
// 否则返回false
// 2.获取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 ");
// 3遍历所有字段
Field[] fArray = c.getDeclaredFields();
for (Field field : fArray) {
// 4拿到每个字段对应的sql
// 4.1字段名
boolean fExists = field.isAnnotationPresent(Column.class);// 是否存在
// 判断是否存在字段
if (!fExists) {
continue;
}
Column column = field.getAnnotation(Column.class);
String columnName = column.value();
Object fieldValue = null;
String filedName = field.getName();
// 4.2拿到字段值（先获取字段的get方法）
String getMethodName = "get"
+ filedName.substring(0, 1).toUpperCase()
+ filedName.substring(1);
try {
Method getMethod = c.getMethod(getMethodName);// 取得该值
// 反射渠道得到字段值
fieldValue = getMethod.invoke(f);
} catch (SecurityException e) {
// TODO Auto-generated catch block
e.printStackTrace();
} catch (NoSuchMethodException e) {
// TODO Auto-generated catch block
e.printStackTrace();
} catch (IllegalArgumentException e) {
// TODO Auto-generated catch block
e.printStackTrace();
} catch (IllegalAccessException e) {
// TODO Auto-generated catch block
e.printStackTrace();
} catch (InvocationTargetException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
if (fieldValue == null
|| (fieldValue instanceof Integer && (Integer) fieldValue == 0)) {
continue;
}
//4.3拼装sql
sb.append("and ").append(columnName);
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("‘,");
}
sb.deleteCharAt(sb.length() - 1);
sb.append(")");
} else {
sb.append("= ‘").append(fieldValue).append("‘");
}
} else {
sb.append("=").append(fieldValue.toString());
}
}
return sb.toString();
}
}
本文出自 “ruanjianlin” 博客，请务必保留此出处http://ruanjianlin.blog.51cto.com/11146685/1900584
Java注解项目实战即模拟Hibenernate生成sql语句
原文：http://ruanjianlin.blog.51cto.com/11146685/1900584