自己动手写泛型dao
在经过一系列的问题得到解决之后，泛型dao终于写出来了。泛型dao相比于以前写的dao最大的好处就是，大大提高了代码的复用性，以往我们要对数据库中表中的数据进行操作的时候，每张表都需要写一个dao来操作，当表非常多的时候，代码量就会很大，还有就是这些代码大部分都是重复的，获取数据库连接、sql预处理，返回结果集，最后关闭数据库连接，获取数据库连接和关闭资源可以放在一个数据库工具类中很简单，剩下的对数据进行操作的方法，由于我们事先不知道要对那张表进行操作，所以就需要利用一些特殊的手段来获取，动态的获取，利用反射这个特性，我们可以很容易的获得我们想要得到的信息。
在前面有一篇文章讲了反射获取类中信息的例子： 通过反射获取属性名和属性类型 这篇文章就是在这里遇到的问题
还有就是在存储获得到的数据时候，需要用到有序的键值对在：有序的Map集合--LinkedHashMap 中说明了
下面开始正题：
代码结构：
在例子中用到了c3p0和读取properties配置文件连接数据库，构建数据库连接池，在第一个方法中写了注释，剩下的方法都是类似的
注意：代码中有get和getset方法分别是拼接get方法和set方法的方法……还有获得属性信息的getField方法都在代码的最后面
package com_basedao;
import java.util.List;
/**
* Created with IDEA
* author:DuzhenTong
* Date:2017/11/8
* Time:19:40
*/
public interface BaseDao<T> {
void update(T t, String password, int id);
void insert(T t);
void delete(T t, int id);
List selectAll(T t);
List selectOne(T t,int id);
}
package com_daoImp;
import com_basedao.BaseDao;
import com_util.JdbcUtil;
import java.lang.reflect.Field;
import java.lang.reflect.InvocationTargetException;
import java.lang.reflect.Method;
import java.sql.Connection;
import java.sql.PreparedStatement;
import java.sql.ResultSet;
import java.sql.SQLException;
import java.util.*;
/**
* Created with IDEA
* author:DuzhenTong
* Date:2017/11/8
* Time:19:46
*/
public class BaseDaoImp<T> implements BaseDao<T>{
private Connection connection;
private PreparedStatement preparedStatement;
private ResultSet resultSet;
private String sql;
private List<Object> list = null;
//LinkedHashMap是一个有顺序的map集合
private static Map<String, String> map = new LinkedHashMap<String, String>();
/**
* 查询表中所有数据
* @param t
* @return
*/
@Override
public List<Object> selectAll(T t) {
//初始化字符串
StringBuffer stringBuffer = new StringBuffer("select * from ");
//创建对象的容器list集合
list = new ArrayList<Object>();
//获取类的类
Class clazz =t.getClass();
//获取到类的名字处理拼接sql语句
sql = stringBuffer.append(clazz.getSimpleName()).toString().toLowerCase();
try {
connection = JdbcUtil.getInstance().getConnection();
preparedStatement = connection.prepareStatement(sql);
resultSet = preparedStatement.executeQuery();
while (resultSet.next()) {
//利用反射获得对象
Object object = clazz.newInstance();
getField(object);
int i = 1;
//遍历map集合
for (Map.Entry<String, String> entry : map.entrySet()) {
if ("int".equals(entry.getValue())) {
//利用发射获取实体类中的set方法
Method method = clazz.getMethod(getSet(entry.getKey()), int.class);
//执行方法
method.invoke(object, resultSet.getInt(i));
//从结果集中想要获取列值需要一个计数器如果查到的是本列加一
i++;
}
if ("String".equals(entry.getValue())) {
Method method = clazz.getMethod(getSet(entry.getKey()), String.class);
method.invoke(object, resultSet.getString(i));
i++;
}
}
list.add(object);
}
} catch (SQLException e) {
e.printStackTrace();
} catch (IllegalAccessException e) {
e.printStackTrace();
} catch (InstantiationException e) {
e.printStackTrace();
} catch (NoSuchMethodException e) {
e.printStackTrace();
} catch (InvocationTargetException e) {
e.printStackTrace();
}finally {
JdbcUtil.releaseResources(connection,preparedStatement,resultSet);
}
return list;
}
/**
* 根据id查询
* @param t
* @param id
* @return
*/
@Override
public List<Object> selectOne(T t,int id) {
StringBuffer stringBuffer = new StringBuffer("select * from ");
list = new ArrayList<Object>();
Class clazz = t.getClass();
sql = stringBuffer.append(clazz.getSimpleName()+" where id=?").toString().toLowerCase();
try {
connection = JdbcUtil.getInstance().getConnection();
preparedStatement = connection.prepareStatement(sql);
preparedStatement.setInt(1,id);
resultSet = preparedStatement.executeQuery();
while (resultSet.next()) {
Object object = clazz.newInstance();
getField(t);
int i = 1;
for (Map.Entry<String, String> entry : map.entrySet()) {
if ("int".equals(entry.getValue())) {
Method method = clazz.getMethod(getSet(entry.getKey()), int.class);
method.invoke(object, resultSet.getInt(i));
i++;
}
if ("String".equals(entry.getValue())) {
Method method = clazz.getMethod(getSet(entry.getKey()), String.class);
method.invoke(object, resultSet.getString(i));
i++;
}
}
list.add(object);
}
} catch (SQLException e) {
e.printStackTrace();
} catch (IllegalAccessException e) {
e.printStackTrace();
} catch (InstantiationException e) {
e.printStackTrace();
} catch (NoSuchMethodException e) {
e.printStackTrace();
} catch (InvocationTargetException e) {
e.printStackTrace();
}finally {
JdbcUtil.releaseResources(connection,preparedStatement,resultSet);
}
return list;
}
/**
* 根据id删除记录
* @param t
* @param id
*/
@Override
public void delete(T t, int id){
StringBuffer stringBuffer = new StringBuffer("delete from ");
Class clazz = t.getClass();
String tableName = clazz.getSimpleName().toLowerCase();
sql = stringBuffer.append(tableName + " where id=?").toString();
try {
connection = JdbcUtil.getInstance().getConnection();
preparedStatement = connection.prepareStatement(sql);
preparedStatement.setInt(1, id);
preparedStatement.execute();
} catch (SQLException e) {
e.printStackTrace();
}finally {
JdbcUtil.releaseResources(connection, preparedStatement, null);
}
}
/**
* 修改密码
* @param t
* @param password
* @param id
*/
@Override
public void update(T t, String password, int id) {
Class clazz = t.getClass();
String tableName = clazz.getSimpleName().toLowerCase();
StringBuffer stringBuffer = new StringBuffer("update " + tableName + " set password=? where id=?");
sql = stringBuffer.toString();
try {
connection = JdbcUtil.getInstance().getConnection();
preparedStatement = connection.prepareStatement(sql);
preparedStatement.setString(1, password);
preparedStatement.setInt(2, id);
preparedStatement.execute();
} catch (SQLException e) {
e.printStackTrace();
} finally {
JdbcUtil.releaseResources(connection, preparedStatement, null);
}
}
/**
* 增加记录
* @param t
*/
@Override
public void insert(T t) {
StringBuffer stringBuffer = new StringBuffer("insert into ");
Class clazz = t.getClass();
String table = clazz.getSimpleName().toLowerCase();
try {
Object object = t;
getField(object);
stringBuffer.append(table + " values(");
for (int i = 0; i < map.size(); i++) {
if (i == map.size() - 1) {
stringBuffer.append("?)");
}else {
stringBuffer.append("?,");
}
}
sql = stringBuffer.toString();
connection = JdbcUtil.getInstance().getConnection();
preparedStatement = connection.prepareStatement(sql);
System.out.println(sql);
int i=1;
for (Map.Entry<String, String> entry : map.entrySet()) {
if ("int".equals(entry.getValue())) {
Method method = clazz.getMethod(get(entry.getKey()));
System.out.println(method.invoke(object,null));
preparedStatement.setInt(i,(int)method.invoke(object,null));
i++;
}
if ("String".equals(entry.getValue())) {
Method method = clazz.getMethod(get(entry.getKey()));
preparedStatement.setString(i,(String)method.invoke(object,null));
i++;
}
}
preparedStatement.execute();
} catch (IllegalAccessException e) {
e.printStackTrace();
} catch (SQLException e) {
e.printStackTrace();
} catch (NoSuchMethodException e) {
e.printStackTrace();
} catch (InvocationTargetException e) {
e.printStackTrace();
}finally {
JdbcUtil.releaseResources(connection,preparedStatement,null);
}
}
/**
* 根据属性名拼接set方法字符串
* @param str
* @return
*/
public static String getSet(String str) {
return "set" + str.substring(0, 1).toUpperCase() + str.substring(1);
}
/**
* 拼接get方法
* @param str
* @return
*/
public static String get(String str) {
return "get" + str.substring(0, 1).toUpperCase() + str.substring(1);
}
public static void getField(Object object) {
Class clazz = object.getClass();
// 获取实体类的所有属性，返回Field数组
Field[] fields = clazz.getDeclaredFields();
for (Field field : fields) {
String type = field.getGenericType().toString();
/*如果是String听会带有class java.lang.String截取再放入map中，其他直接放入
* 把属性名作为键，属性类型作为值*/
if ("class java.lang.String".equals(type)) {
int index = type.lastIndexOf(".");
map.put(field.getName(), type.substring(index + 1));
} else {
map.put(field.getName(), field.getGenericType().toString());
}
}
}
}
数据库工具类：JdbcUtil 用到了单例模式
package com_util;
import com.mchange.v2.c3p0.ComboPooledDataSource;
import java.beans.PropertyVetoException;
import java.io.IOException;
import java.io.InputStream;
import java.sql.Connection;
import java.sql.PreparedStatement;
import java.sql.ResultSet;
import java.sql.SQLException;
import java.util.Properties;
public class JdbcUtil {
private Properties properties = new Properties();
private static String dirverName;
private static String url;
private static String username;
private static String password;
private static ComboPooledDataSource dataSource;
private static JdbcUtil jdbcUtil = new JdbcUtil();
private JdbcUtil() {
try {
InputStream inputStream = JdbcUtil.class.getClassLoader()
.getResourceAsStream("datebase.properties");
// 从输入字节流读取属性列表（键和元素对）
properties.load(inputStream);
// 用此属性列表中指定的键搜索属性，获取驱动，url，username，password
dirverName = properties.getProperty("driverName").trim();
url = properties.getProperty("url").trim();
username = properties.getProperty("username").trim();
password = properties.getProperty("password").trim();
dataSource = new ComboPooledDataSource();
dataSource.setUser(username);
dataSource.setPassword(password);
dataSource.setJdbcUrl(url);
dataSource.setDriverClass(dirverName);
dataSource.setInitialPoolSize(5); //初始化连接数
dataSource.setMinPoolSize(1);//最小连接数
dataSource.setMaxPoolSize(20);//最大连接数
dataSource.setMaxStatements(50);//最长等待时间
dataSource.setMaxIdleTime(60);//最大空闲时间，单位毫秒
} catch (PropertyVetoException e) {
e.printStackTrace();
} catch (IOException e) {
e.printStackTrace();
}
}
public static JdbcUtil getInstance(){
return jdbcUtil;
}
public synchronized Connection getConnection() {
Connection conn = null;
try {
conn=dataSource.getConnection();
} catch (SQLException e) {
e.printStackTrace();
}
return conn;
}
//关闭连接工具方法
public static void releaseResources(Connection connection, PreparedStatement preparedStatement, ResultSet resultSet) {
if (resultSet != null) {
try {
resultSet.close();
} catch (SQLException e) {
e.printStackTrace();
}
}
if (connection != null) {
try {
connection.close();
} catch (SQLException e) {
e.printStackTrace();
}
}
if (preparedStatement != null) {
try {
preparedStatement.close();
} catch (SQLException e) {
e.printStackTrace();
}
}
}
}
实体类：用于测试
package com_domain;
public class Users {
private int id;
private String name;
private String password;
private int aid;
@Override
public String toString() {
return "Users{" +
"id=" + id +
", name='" + name + '\'' +
", password='" + password + '\'' +
", aid=" + aid +
'}';
}
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 getPassword() {
return password;
}
public void setPassword(String password) {
this.password = password;
}
public int getAid() {
return aid;
}
public void setAid(int aid) {
this.aid = aid;
}
}
datebase.properties数据库连接配置文件
driverName=com.mysql.jdbc.Driver url=jdbc:mysql://localhost:3306/test username=root password=root
代码放在了github上，可以下载完整代码（Code_story仓库fanxing文件夹）：https://github.com/Ai-yoo/Code_story.git
