使用JAVA反射的利与弊_JAVA_编程开发_程序员俱乐部

class="java" name="code">package com.qin.model;

public class Dog {
	
	private int id;
	private String name;
	private String type;
	private String color;
	private int weight;
	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 getType() {
		return type;
	}
	public void setType(String type) {
		this.type = type;
	}
	public String getColor() {
		return color;
	}
	public void setColor(String color) {
		this.color = color;
	}
	public int getWeight() {
		return weight;
	}
	public void setWeight(int weight) {
		this.weight = weight;
	}
 public Dog() {
	// TODO Auto-generated constructor stub
}
public Dog(int id, String name, String type, String color, int weight) {
	super();
	this.id = id;
	this.name = name;
	this.type = type;
	this.color = color;
	this.weight = weight;
}
@Override
public String toString() {
	return "Dog [id=" + id + ", name=" + name + ", type=" + type + ", color="
			+ color + ", weight=" + weight + "]";
}


 
	
}

package com.qin.model;

public class Person {
	
	private int id;
	private String name;
	private int age;
	private String address;
	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 int getAge() {
		return age;
	}
	public void setAge(int age) {
		this.age = age;
	}
	public String getAddress() {
		return address;
	}
	public void setAddress(String address) {
		this.address = address;
	}
	
	public Person() {
		// TODO Auto-generated constructor stub
	}
	public Person(int id, String name, int age, String address) {
		super();
		this.id = id;
		this.name = name;
		this.age = age;
		this.address = address;
	}
	@Override
	public String toString() {
		return "Person [id=" + id + ", name=" + name + ", age=" + age
				+ ", address=" + address + "]";
	}
	
	

}

package com.qin.db;

import java.sql.Connection;
import java.sql.DriverManager;
import java.sql.PreparedStatement;
import java.sql.ResultSet;
/**
 * 数据库连接的
 * 测试类
 * @author qindongliang
 * 
 * 
 * **/
public class ConnectionFactory {
	
	public static Connection getCon()throws Exception{
		Class.forName("com.mysql.jdbc.Driver");
		//加上字符串编码指定，防止乱码
		Connection connection = DriverManager.getConnection("jdbc:mysql://localhost:3306/rate?characterEncoding=utf8", "root", "qin");
		return connection;
	}
	
	
	public static void main(String[] args) throws Exception {
		
		Class.forName("com.mysql.jdbc.Driver");
		Connection connection = DriverManager.getConnection("jdbc:mysql://localhost:3306/rate", "root", "qin");
		System.out.println(connection);
		connection.close();
		
		
	}

}

package com.qin.commons;

import java.lang.reflect.Field;
import java.lang.reflect.Method;
import java.sql.Connection;
import java.sql.PreparedStatement;
import java.sql.ResultSet;
import java.util.ArrayList;
import java.util.List;

import com.qin.db.ConnectionFactory;
import com.qin.model.Dog;
import com.qin.model.Person;
/***
 * 反射自动查询和封装的类
 *@author qindongliang 
 * 
 * */
public class CommonSupport {
	
	
	/**
	 * @param obj需要保存的对象
	 * @param string 保存对象的sql语句
	 * */
	public static String createSqlByObject(Object obj){
		
		 StringBuffer sb=new StringBuffer("insert into ");
		
		//得到对象的类
		Class c=obj.getClass();
		//得到对象中的所有方法
		Method[] ms=c.getMethods();
		
		//得到对象中所有的属性,虽然在这个里面就能获取所有的字段名，但不建议这么用，破坏类的封装性
		Field[]  fs=c.getDeclaredFields();
		//得到对象类的名字
		String cname=c.getName();
		System.out.println("类名字： "+cname);
		//表名字
		String tableName=cname.split("\\.")[cname.split("\\.").length-1];
		System.out.println("表名字： "+tableName);
		//追加表名和（左边的符号
		sb.append(tableName).append(" (");
		//存放列名的集合
		List<String> columns=new ArrayList<String>();
		//存放值的集合
		List values=new ArrayList();
		//遍历方法
		for(Method m:ms){
			 String methodName=m.getName();//获取每一个方法名
			 //只得到具有get方法的属性，getClass除外
			 if(methodName.startsWith("get")&&!methodName.startsWith("getClass")){
				 //System.out.println("属性名："+methodName);
				 String fieldName = methodName.substring(3, methodName.length());
//				 System.out.println("字段名："+fieldName);
				 columns.add(fieldName);//将列名添加到列名的集合里
				 try{
					 Object value=m.invoke(obj, null);
					 //System.out.println("执行方法返回的值："+value);
					 if(value instanceof String){
//						 System.out.println("字符串类型字段值："+value);
						 values.add("'"+value+"'");//加上两个单引号，代表是字符串类型的
					 }else{
//						 System.out.println("数值类型字段值："+value);
						 values.add(value);//数值类型的则直接添加
					 }
					 
				 }catch(Exception e){
					 e.printStackTrace();
				 }
				 
			 }
		
		}
		
		
		for(int i=0;i<columns.size();i++){
			String column=columns.get(i);
			Object value=values.get(i);
			System.out.println("列名："+column+" 值：  "+value);
		}
		
		//拼接列名
		for(int i=0;i<columns.size();i++){
			 if(i==columns.size()-1){
				 sb.append(columns.get(i)).append(" ) ");
			 }else{
				 sb.append(columns.get(i)).append(" , ");
			 }
		}
		System.out.println(" 拼接列名后的sql："+sb.toString());
		sb.append(" values ( ");
		//拼接值
		for(int i=0;i<values.size();i++){
			 if(i==values.size()-1){
				 sb.append(values.get(i)).append(" ) ");
			 }else{
				 sb.append(values.get(i)).append(" , ");
			 }
		}
	
		System.out.println(" 拼接值后的sql："+sb.toString());
  
		//返回组装的sql语句
		return sb.toString();
	}
	
	/**
	 * 将对象保存在数据库中
	 * @param obj 保存的对象
	 * **/
	public static void addOne(Object obj){
		try {
			Connection con=ConnectionFactory.getCon();
			String sql=createSqlByObject(obj);
			PreparedStatement ps=con.prepareStatement(sql);
			int result=ps.executeUpdate();
			if(result==1){
				System.out.println("保存成功！");
			}else{
				System.out.println("保存失败！");
			}
			ps.close();
			con.close();
		} catch (Exception e) {
			// TODO Auto-generated catch block
			e.printStackTrace();
		}
		
	}
	
	/**
	 * 根据类名字和一个查询条件
	 * 自动封装一个Bean对象
	 * @param columnName 列名
	 * @param value 列值
	 * @return {@link Object}
	 * 
	 * */
	public static Object getOneObject(String className,String columnName,String value){
		
		String tableName=className.split("\\.")[className.split("\\.").length-1];
		System.out.println("表名字： "+tableName);
		
		//根据类名来创建对象
		Class c=null;
		try{
			c=Class.forName(className);//反射生成一个类实例
		}catch(Exception e){
			e.printStackTrace();
		}
		//拼接sql语句
		StringBuffer sb=new StringBuffer();
		sb.append("select * from ")
		.append(tableName)
		.append(" where ")
		.append(columnName).append(" = ").append("'").append(value).append("'");
		
		String querySql=sb.toString();
		System.out.println("查询的sql语句为:"+querySql);
		
		Object obj=null;
		try{
		Connection con=ConnectionFactory.getCon();//得到一个数据库连接
		PreparedStatement ps=con.prepareStatement(querySql);//预编译语句
		ResultSet rs=ps.executeQuery();//执行查询
		//得到对象的所有的方法
		Method ms[]=c.getMethods();
		
		if(rs.next()){
			//生成一个实例
			obj=c.newInstance();
			
			for(Method m:ms){
				String mName=m.getName();
				if(mName.startsWith("set")){
					//根据方法名字自动提取表中对应的列名
					  String cname = mName.substring(3, mName.length());
					  //打印set的方法名
					 // System.out.println(cname);
					//得到方法的参数类型
					  Class[] params=m.getParameterTypes();
//					  for(Class cp : params){
//						  System.out.println(cp.toString());
//					  }
					  //如果参数是String类型，则从结果集中，按照列名取到的值，进行set
					  //从params[0]的第一个值，能得到该数的参数类型
					  if(params[0]==String.class){//
						  m.invoke(obj, rs.getString(cname));
					  //如果判断出来是int形，则使用int
					  }else if(params[0]==int.class){
						  m.invoke(obj, rs.getInt(cname));
					  }
				}
			}
			
			
			
		}else{
			System.out.println("请注意："+columnName+"="+value+"的条件，没有查询到数据!!");
		}
		rs.close();
		ps.close();
		con.close();
		}catch(Exception e){
			e.printStackTrace();
		}
		
		
		
		return obj;
	}
	
	
	
	
	public static void main(String[] args) throws Exception{
		//====================添加======================
		Dog d=new Dog(21, "小不点", "藏獒", "灰色", 25);
		Person p=new Person(6, "大象hadoop", 10, "家住Apache基金组织");
		 //createSqlByObject(d);
		//addOne(d);给dog表添加一条数据
		//addOne(p);//给person表添加一条数据
		
		//=======================查询=======================
		//强制转换为原始类
//	  Dog d1=(Dog)getOneObject("com.qin.model.Dog", "id", "1");
//	  System.out.println(d1);
		
		Person d1=(Person)getOneObject("com.qin.model.Person", "id", "1");
		//Person d1=(Person)getOneObject("com.qin.model.Person", "name", "王婷");
	    System.out.println(d1);
	  
	  
	}
	 
	

}

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