注解学习实例(模拟hibernate，table,column注解，拼装SQL)

直接上代码

package com.guoxinet.o2o.annotation;

import java.lang.annotation.Documented;
import java.lang.annotation.ElementType;
import java.lang.annotation.Inherited;
import java.lang.annotation.Retention;
import java.lang.annotation.RetentionPolicy;
import java.lang.annotation.Target;

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

　　

package com.guoxinet.o2o.annotation;

import java.lang.annotation.Documented;
import java.lang.annotation.ElementType;
import java.lang.annotation.Inherited;
import java.lang.annotation.Retention;
import java.lang.annotation.RetentionPolicy;
import java.lang.annotation.Target;

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

　　

package com.guoxinet.o2o.annotation;
@Table("tb_user")
public class User {
    @Column("user_id")
    private int userId;
    
    @Column("user_name")
    private String userName;
    
    @Column("address")
    private String address;
    
    @Column("email")
    private String email;

    public int getUserId() {
        return userId;
    }

    public void setUserId(int userId) {
        this.userId = userId;
    }

    public String getUserName() {
        return userName;
    }

    public void setUserName(String userName) {
        this.userName = userName;
    }

    public String getAddress() {
        return address;
    }

    public void setAddress(String address) {
        this.address = address;
    }

    public String getEmail() {
        return email;
    }

    public void setEmail(String email) {
        this.email = email;
    }

}

package com.guoxinet.o2o.annotation;
@Table("tb_department")
public class DepartMent {
    @Column("department_id")
    private int departmentId;
    
    @Column("name")
    private String name;

    public int getDepartmentId() {
        return departmentId;
    }

    public void setDepartmentId(int departmentId) {
        this.departmentId = departmentId;
    }

    public String getName() {
        return name;
    }

    public void setName(String name) {
        this.name = name;
    }
    
    

}

package com.guoxinet.o2o.annotation;

import java.lang.reflect.Field;
import java.lang.reflect.Method;

public class Client {
    
    public static void main(String[] args) {
        User user = new User();
        user.setUserId(1);
        user.setEmail("3964412@qq.com,yafeng@yahu.com,lifeng@guoxinet.com");
        getSql(user);
        
        DepartMent dm = new DepartMent();
        dm.setDepartmentId(100);
        dm.setName("技术部");
        getSql(dm);
    }
    
    public static String getSql(Object ob){
        StringBuilder sb = new StringBuilder();
        //获取class
        @SuppressWarnings("rawtypes")
        Class c = ob.getClass();
        //获取table的名字
        @SuppressWarnings("unchecked")
        boolean isExist = c.isAnnotationPresent(Table.class);
        if(!isExist){
            return "";
        }
        Table table = (Table)c.getAnnotation(Table.class);
        
        String tableName = table.value();
        sb.append("select * from ").append(tableName).append(" where 1=1 ");
        //遍历属性
        Field[] fArray =c.getDeclaredFields();
        for(Field field: fArray){
            boolean fisExist = field.isAnnotationPresent(Column.class);
            if(!fisExist){
                continue;
            }
            Column column = (Column)field.getAnnotation(Column.class);
            //列名
            String columnName = column.value();
            //得到属性的值
            String methodName = "get" +field.getName().substring(0,1).toUpperCase() + field.getName().substring(1);
            Object fieldValue = null;
            try {
                Method method = c.getMethod(methodName);
                fieldValue = method.invoke(ob);
                if(null == fieldValue || (fieldValue instanceof Integer && 0 == (Integer)fieldValue) ){
                    System.out.println(fieldValue);
                    continue;
                }
                sb.append(" and ").append(columnName);
                if(fieldValue instanceof String){
                    if(((String) fieldValue).contains(",")){
                        String[] sArray = ((String) fieldValue).split(",");
                        sb.append(" in ").append("(");
                        for(String s : sArray){
                            sb.append("'").append(s).append("',");
                        }
                        sb.deleteCharAt(sb.length()-1);
                        sb.append(")");
                    }else{
                        sb.append(" = ");
                        sb.append("'").append(fieldValue).append("'");
                    }
                    
                }else{
                    sb.append(" = ").append(fieldValue);
                }
                
            } catch (Exception e) {
                // TODO Auto-generated catch block
                e.printStackTrace();
            } 
        }
        sb.append(";");
        System.out.println(sb.toString());
        return null;
    }

}