<
---
@Target 表示注解的一个作用域
ElementType.CONSTRUCTOR 构造方法声明
ElementType.FIELD 字段声明
ElementType.LOCAL_VARIABLE 局部变量声明
ElementType.METHOD 方法声明
ElementType.PACKAGE 包声明
ElementType.PARAMETER 参数声明
ElementType.TYPE 类声明
---
@Retention 生命周期
RetentionPolicy.SOURCE 只在源码显示，编译时会丢弃
RetentionPolicy.CLASS 编译时会记录到class中，运行时忽略
RetentionPolicy.RUNTIME 运行时存在，可以通过反射读取
---
@Inherited 标识性的元注解 标识允许子类注解来继承它, **注解继承只会继承到类，不会继承到里面的方法。**
---
@Documented 生成javadoc时，会包含注解
---
####使用自定义注解
语法：
@<注解名>(<成员名1>=<成员值1>,<成员名2>=<成员值3>,...)
```
package com.lgd.anno.define;
/**
* Created by liguodong on 2016/1/27.
*/
@Desciption(desc = "I have class double eyeColor.",author = "wintfru",age = 22)
public class EyeColor {
@Desciption(desc = "I have method double eyeColor.",author = "wintfru",age = 22)
public String eyeColor(){
return "red";
}
}
```
**测试**
```
package com.lgd.anno.define;
import java.lang.annotation.Annotation;
import java.lang.reflect.Method;
/**
* Created by liguodong on 2016/1/27.
*/
public class ParseAnnoMain {
public static void main(String[] args) {
try {
//1.使用类加载器加载类
Class c = Class.forName("com.lgd.anno.define.EyeColor");
//2.找到类上面的注解
boolean isExist = c.isAnnotationPresent(Desciption.class);
if(isExist){
//3.拿到注解实例
Desciption d = (Desciption) c.getAnnotation(Desciption.class);
System.out.println(d.desc()+"<--->"+d.author()+"<--->"+d.age());
//4.找到方法上的注解
Method[] ms = c.getMethods();
for(Method m:ms){
boolean isMExist = m.isAnnotationPresent(Desciption.class);
if(isMExist){
Desciption dm = (Desciption) m.getAnnotation(Desciption.class);
System.out.println(dm.desc()+"<--->"+dm.author()+"<--->"+dm.age());
}
}
//另外一种解析方法
for(Method m:ms){
Annotation[] as = m.getAnnotations();
for (Annotation a:as){
if(a instanceof Desciption){
Desciption dm2 = (Desciption)a;
System.out.println(dm2.desc()+"<--->"+dm2.author()+"<--->"+dm2.age());
}
}
}
}
} catch (ClassNotFoundException e) {
e.printStackTrace();
}
}
}
```
运行结果：
`I have class double eyeColor.<--->wintfru<--->22`
`I have method double eyeColor.<--->wintfru<--->22`
`I have method double eyeColor.<--->wintfru<--->22`
###注解实战
**需求：**
1.有一张用户表，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。
2.方便的对每个字段或字段的组合条件进行检索，并打印出SQL。
3.使用方式简单。
```
package com.lgd.application;
import java.lang.annotation.ElementType;
import java.lang.annotation.Retention;
import java.lang.annotation.RetentionPolicy;
import java.lang.annotation.Target;
/**
* Created by liguodong on 2016/1/27.
*/
@Target({ElementType.TYPE})
@Retention(RetentionPolicy.RUNTIME)
public @interface Table {
String value();
}
```
```
package com.lgd.application;
import java.lang.annotation.ElementType;
import java.lang.annotation.Retention;
import java.lang.annotation.RetentionPolicy;
import java.lang.annotation.Target;
/**
* Created by liguodong on 2016/1/27.
*/
@Target({ElementType.FIELD})
@Retention(RetentionPolicy.RUNTIME)
public @interface Column {
String value();
}
```
```
package com.lgd.application;
/**
* Created by liguodong on 2016/1/27.
*/
@Table("user")
public class FilterUser {
@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;
}
}
```
```
package com.lgd.application;
/**
* Created by liguodong on 2016/1/28.
*/
@Table("department")
public class FilterDepartment {
@Column("id")
private int id;
@Column("name")
private String name;
@Column("leader")
private String leader;
@Column("amount")
private int amount;
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 getLeader() {
return leader;
}
public void setLeader(String leader) {
this.leader = leader;
}
public int getAmount() {
return amount;
}
public void setAmount(int amount) {
this.amount = amount;
}
}
```
```
package com.lgd.application;
import org.apache.commons.logging.Log;
import org.apache.commons.logging.LogFactory;
import java.lang.reflect.Field;
import java.lang.reflect.Method;
import java.util.regex.Matcher;
import java.util.regex.Pattern;
/**
* Created by liguodong on 2016/1/27.
*/
public class Main {
//匹配邮箱
//([a-zA-Z0-9_\.\-])+\@(([a-zA-Z0-9\-])+\.)+([a-zA-Z0-9]{2,5})+
private static String regex = "([a-zA-Z0-9_\\.\\-])+\\@(([a-zA-Z0-9\\-])+\\.)+([a-zA-Z0-9]{2,5})+";
private static Log log = LogFactory.getLog(Main.class);
public static void main(String[] args) {
FilterUser f1 = new FilterUser();
f1.setId(10); //查询id为10的用户
FilterUser f2 = new FilterUser();
f2.setUsername("wintfru"); //查询用户名为wintfru的用户
f2.setAge(22);
f2.setEmail("liguodong@163.com");
//查询邮箱为其中任意一个的用户
FilterUser f3 = new FilterUser();
f3.setEmail("liguodong@163.com; 66668888@qq.com; thinkpad@sina.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);
FilterDepartment fd1 = new FilterDepartment();
fd1.setName("项目研发部");
fd1.setAmount(10);;
String sql4 = query(fd1);
System.out.println(sql4);
}
public static String query(Object filter){
StringBuilder sb = new StringBuilder();
//1.获取到class
Class c = filter.getClass();
//2.获取到table的名字
boolean exists = c.isAnnotationPresent(Table.class);
if(!exists){
return null;
}
Table table = (Table)c.getAnnotation(Table.class);
String tableName = table.value(); //表名
sb.append("select * from ").append(tableName).append(" where 1=1");
//3.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 columnName = column.value(); //字段名 注解上面的值
log.info("columnName:"+columnName);
log.info("fieldName:"+field.getName());
//4.2 拿到字段的值
String fieldName = field.getName(); //属性值
String getMethodName = "get" +
fieldName.substring(0,1).toUpperCase() +
fieldName.substring(1);
Object fieldValue = null;
try {
Method getMethod = c.getMethod(getMethodName);
//通过反射调用
fieldValue = getMethod.invoke(filter,null);
} catch (Exception e) {
e.printStackTrace();
}
if(fieldValue == null || (fieldValue instanceof Integer && (Integer)fieldValue ==0)) {
continue;
}
//4.3 拼装sql
sb.append(" and ").append(fieldName);
if (fieldValue instanceof String){
Pattern pattern = Pattern.compile(regex);
Matcher matcher = pattern.matcher((String)fieldValue);
if(!matcher.find()) {
sb.append(" = ").append("'").append(fieldValue).append("'");
}
else{
sb.append(" in ( ");
String temp = matcher.group();
sb.append("'").append(temp).append("'");
while (matcher.find()){
temp = matcher.group();
sb.append(", ").append("'").append(temp).append("'");
}
sb.append(" )");
}
}else if(fieldValue instanceof Integer){
sb.append(" = ").append(fieldValue);
}
}
return sb.toString();
}
}
```
运行结果：
`select * from user where 1=1 and id = 10`
`select * from user where 1=1 and username = 'wintfru' and age = 22 and email in ( 'liguodong@163.com' )`
`select * from user where 1=1 and email in ( 'liguodong@163.com', '66668888@qq.com', 'thinkpad@sina.com' )`
`select * from department where 1=1 and name = '项目研发部' and amount = 10`
**项目源码地址：**
`https://github.com/liguodongIOT/JavaFrames/tree/master/AnnocationProject`
]]>