1. 分析jdbc操作问题
1.1 数据库连接创建、释放频繁造成系统资源浪费,从而影响系统性能。
1.2 Sq|语句在代码中硬编码, 造成代码不易维护,实际应用中sq|变化的可能较大,sq|变动需要改变java代码。
1.3 使用preparedStatement向 占有位符号传参数存在硬编码,因为sq|语句的where条件不一 定,可能多也可能少,修改sq|还要修改代码,系统不易维护。
1.4 对结果集解析存在硬编码(查询列名),sq|变化导 致解析代码变化,系统不易维护,如果能将数据库记录封装成pojo对象解析比较方便
2.问题解决思路
2.1 数据库频繁创建连接、释放资源:连接池
2.2 sq|语句及参数硬编码:配置文件
2.3手动解析封装返回结果集:反射、内省
3.自定义框架设计
3.1 提供核心配置文件
3.2 sqlMapConfig.xml:存放数据源信息,引入mapper.xml
3.3 Mapper .xml: sql语句的配置文件信息
3.4 实现步骤:
3.4.1.读取配置文件
3.4.2 创建javaBean来存储
-(1) Configuration: 存放数据库基本信息、Map<唯一标识,Mapper> 唯一标识: namespace+"."+id
-(2) MappedStatement: sql语句、statement类型 、输入参数java类型、输出参数java类型
3.4.3 解析配置文件
3.4.3.1 创建SqISessionFactroyBuilder类: 方法: SqlSessionFactory build():
第一:使用dom4j解析配置文件,将解析出来的内容封装到Configuration和MappedStatement中
第二:创建SqlSessionFactory的实现类DefaultSqISession
3.4.4 创建SqlSessionFactory: 方法: openSession(): 获取sqlSession接口的实 现类实例对象
3.4.5 创建SqISession接口及实现类:主要封装CRUD方法 具体实现:封装JDBC完成对数据库表的查询操作
4.自定义持久层框架的实现:
创建sqlMapConfig.xml 文件
<!--数据库配置信息-->
<property name="driverClass" value="com.mysql.jdbc.Driver">
<property name="jdbcUrl" value="jdbc:mysql://192.168.0.125/learn">
<property name="username" value="root">
<property name="password" value="root">
<!--存放mapper.xml的全路径-->
<mapper resource="UserMapper.xml">
</configuration>
创建 mapper.xml
<mapper namespace="com.learn.dao.IUserDao">
<!--sql的唯一标识由namespace和id组成 statementId-->
<select id="findAll" resultType="com.learn.pojo.User">
select * from user
</select>
<!-- 多参数传递 使用面向对象 以对象传递-->
<select id="findByCondition" resultType="com.learn.pojo.User" paramterType="com.learn.pojo.User">
select * from user where id = #{id} and username = #{username}
</select>
</mapper>
创建 user 实体
package com.learn.pojo;
/**
* @Author liu
* @Title: User
* @ProjectName IPersistence_test
* @Description: //TODO
* @date 2020/6/19 15:33
*/
public class User {
private Integer id;
private String username;
public Integer getId() {
return id;
}
public void setId(Integer id) {
this.id = id;
}
public String getUsername() {
return username;
}
public void setUsername(String username) {
this.username = username;
}
}
创建maven子模块导入相关依赖
<!--设置jdk编译版本-->
<properties>
<project.build.sourceEncoding>UTF-8</project.build.sourceEncoding>
<maven.compiler.encoding>UTF-8</maven.compiler.encoding>
<java.version>1.8</java.version>
<maven.compiler.source>1.8</maven.compiler.source>
<maven.compiler.target>1.8</maven.compiler.target>
</properties>
<dependencies>
<dependency>
<groupId>mysql</groupId>
<artifactId>mysql-connector-java</artifactId>
<version>5.1.17</version>
</dependency>
<dependency>
<groupId>c3p0</groupId>
<artifactId>c3p0</artifactId>
<version>0.9.1.2</version>
</dependency>
<dependency>
<groupId>log4j</groupId>
<artifactId>log4j</artifactId>
<version>1.2.12</version>
</dependency>
<dependency>
<groupId>junit</groupId>
<artifactId>junit</artifactId>
<version>4.10</version>
</dependency>
<dependency>
<groupId>dom4j</groupId>
<artifactId>dom4j</artifactId>
<version>1.6.1</version>
</dependency>
<dependency>
<groupId>jaxen</groupId>
<artifactId>jaxen</artifactId>
<version>1.1.6</version>
</dependency>
</dependencies>
创建configuration类,此类用来存储datasource以及mapper.xml的配置信息
package com.learn.pojo;
import javax.sql.DataSource;
import java.util.HashMap;
import java.util.Map;
/**
* @Author liu
* @Title: Configuration
* @ProjectName IPersistence_test
* @Description: //TODO
* @date 2020/6/19 12:46
*/
public class Configuration {
private DataSource dataSource;
/**
* key: statementId sql唯一标识 由xml文件中的namespace和id组成
*/
Map<String,MappedStatement> mappedStatementMap = new HashMap<>();
public DataSource getDataSource() {
return dataSource;
}
public void setDataSource(DataSource dataSource) {
this.dataSource = dataSource;
}
public Map<String, MappedStatement> getMappedStatementMap() {
return mappedStatementMap;
}
public void setMappedStatementMap(Map<String, MappedStatement> mappedStatementMap) {
this.mappedStatementMap = mappedStatementMap;
}
}
创建MappedStatement类,此类用来存储mapper.xml的相关信息
package com.learn.pojo;
/**
* @Author liu
* @Title: MappedStatement
* @ProjectName IPersistence_test
* @Description: //TODO
* @date 2020/6/19 12:42
*/
public class MappedStatement {
/**
* 1.id标识
* 2.返回值类型
* 3.参数类型
* sql语句
*/
private String id;
private String resultType;
private String paramterType;
private String sql;
public String getId() {
return id;
}
public void setId(String id) {
this.id = id;
}
public String getResultType() {
return resultType;
}
public void setResultType(String resultType) {
this.resultType = resultType;
}
public String getParamterType() {
return paramterType;
}
public void setParamterType(String paramterType) {
this.paramterType = paramterType;
}
public String getSql() {
return sql;
}
public void setSql(String sql) {
this.sql = sql;
}
}
创建Resources类,此类用来根据配置文件的路径,将配置文件加载成字节输入流,存储在内存中。
package com.learn.io;
import java.io.InputStream;
/**
* @Author liu
* @Title: Resources
* @ProjectName IPersistence_test
* @Description: //TODO
* @date 2020/6/19 12:28
*/
public class Resources {
/**
* 根据配置文件的路径,将配置文件加载成字节输入流,存储在内存中
* @param path 配置文件的路径
* @return
*/
public static InputStream getResourceAsSteam(String path) {
InputStream inputStream = Resources.class.getClassLoader().getResourceAsStream(path);
return inputStream;
}
}
创建SqlSessionFactoryBuilder
package com.learn.sqlsession;
import com.learn.config.XMLConfigBuilder;
import com.learn.pojo.Configuration;
import org.dom4j.DocumentException;
import java.beans.PropertyVetoException;
import java.io.InputStream;
/**
* @Author liu
* @Title: SqlSessionFactoryBuilder
* @ProjectName IPersistence_test
* @Description: //TODO
* @date 2020/6/19 12:53
*/
public class SqlSessionFactoryBuilder {
/**
* 1.使用dom4j解析配置文件,将解析出来的内容封装到configuration中
* 2.创建sqlSessionFactory对象
*
* @param inputStream
* @return
*/
public SqlSessionFactory build(InputStream inputStream) throws DocumentException, PropertyVetoException {
//1.dom4j解析进行封装
XMLConfigBuilder xmlConfigBuilder = new XMLConfigBuilder();
Configuration configuration = xmlConfigBuilder.parseConfig(inputStream);
//2.创建sqlSessionFactory对象: 工厂类:生产sqlSession:会话对象 sqlSession封装 crud方法
DefaultSqlSessionFactory defaultSqlSessionFactory = new DefaultSqlSessionFactory(configuration);
return defaultSqlSessionFactory;
}
}
创建XMLConfigerBuilder类
package com.learn.config;
import com.learn.io.Resources;
import com.learn.pojo.Configuration;
import com.mchange.v2.c3p0.ComboPooledDataSource;
import org.dom4j.Attribute;
import org.dom4j.Document;
import org.dom4j.DocumentException;
import org.dom4j.Element;
import org.dom4j.io.SAXReader;
import java.beans.PropertyVetoException;
import java.io.InputStream;
import java.util.List;
import java.util.Properties;
/**
* @Author liu
* @Title: XMLConfigBuilder
* @ProjectName IPersistence_test
* @Description: //TODO
* @date 2020/6/19 12:58
*/
public class XMLConfigBuilder {
private Configuration configuration;
public XMLConfigBuilder() {
this.configuration = new Configuration();
}
/**
* 该方法就是使用dom4j对配置文件进行解析,封装configuration
*
* @param inputStream
* @return
*/
public Configuration parseConfig(InputStream inputStream) throws DocumentException, PropertyVetoException {
Document document = new SAXReader().read(inputStream);
// 获取根对象 拿到configuration
Element rootElement = document.getRootElement();
List<Element> list = rootElement.selectNodes("//property");
Properties properties = new Properties();
for (Element element : list) {
String name = element.attributeValue("name");
String value = element.attributeValue("value");
properties.setProperty(name, value);
}
ComboPooledDataSource comboPooledDataSource = new ComboPooledDataSource();
comboPooledDataSource.setDriverClass(properties.getProperty("driverClass"));
comboPooledDataSource.setJdbcUrl(properties.getProperty("jdbcUrl"));
comboPooledDataSource.setUser(properties.getProperty("username"));
comboPooledDataSource.setPassword(properties.getProperty("password"));
configuration.setDataSource(comboPooledDataSource);
//mapper.xml 解析: 1.拿到路径 2.根据路径拿到字节输入流 3.dom4j 进行解析
List<Element> mapperList = rootElement.selectNodes("//mapper");
for (Element element : mapperList) {
String mapperPath = element.attributeValue("resource");
InputStream resourceAsSteam = Resources.getResourceAsSteam(mapperPath);
XMLMapperBuilder xmlMapperBuilder = new XMLMapperBuilder(configuration);
xmlMapperBuilder.parse(resourceAsSteam);
}
return configuration;
}
}
创建XMLMapperBuilder类,此类用来解析业务表的xml文件
package com.learn.config;
import com.learn.pojo.Configuration;
import com.learn.pojo.MappedStatement;
import org.dom4j.Document;
import org.dom4j.DocumentException;
import org.dom4j.Element;
import org.dom4j.io.SAXReader;
import java.io.InputStream;
import java.util.List;
/**
* @Author liu
* @Title: XMLMapperBuilder
* @ProjectName IPersistence_test
* @Description: //TODO
* @date 2020/6/19 14:13
*/
public class XMLMapperBuilder {
private Configuration configuration;
public XMLMapperBuilder(Configuration configuration) {
this.configuration = configuration;
}
public void parse(InputStream inputStream) throws DocumentException {
Document document = new SAXReader().read(inputStream);
Element rootElement = document.getRootElement();
String namespace = rootElement.attributeValue("namespace");
//此处只解析了查询操作,其余crud操作举一反三
List<Element> list = rootElement.selectNodes("//select");
for (Element element : list) {
String id = element.attributeValue("id");
String resultType = element.attributeValue("resultType");
String paramterType = element.attributeValue("paramterType");
String sqlText = element.getTextTrim();
MappedStatement mappedStatement = new MappedStatement();
mappedStatement.setId(id);
mappedStatement.setResultType(resultType);
mappedStatement.setParamterType(paramterType);
mappedStatement.setSql(sqlText);
String key = namespace + "." + id;
configuration.getMappedStatementMap().put(key, mappedStatement);
}
}
}
创建sqlSessionFactory݊工厂
package com.learn.sqlsession;
/**
* @Author liu
* @Title: SqlSessionFactory
* @ProjectName IPersistence_test
* @Description: //TODO
* @date 2020/6/19 12:56
*/
public interface SqlSessionFactory {
public SqlSession openSession();
}
创建DefaultSqlSessionFactory
package com.learn.sqlsession;
import com.learn.pojo.Configuration;
/**
* @Author liu
* @Title: DefaultSqlSessionFactory
* @ProjectName IPersistence_test
* @Description: //TODO
* @date 2020/6/19 15:16
*/
public class DefaultSqlSessionFactory implements SqlSessionFactory {
private Configuration configuration;
public DefaultSqlSessionFactory(Configuration configuration) {
this.configuration = configuration;
}
@Override
public SqlSession openSession() {
return new DefaultSqlSession(configuration);
}
}
sqlSession݊接口DefaultSqlSession实现类
package com.learn.sqlsession;
import java.util.List;
/**
* @Author liu
* @Title: SqlSession
* @ProjectName IPersistence_test
* @Description: //TODO
* @date 2020/6/19 15:20
*/
public interface SqlSession {
/**
* 查询所有
* @param <E>
* @param statementId
* @param params
* @return
*/
public <E> List<E> selectList(String statementId,Object... params) throws Exception;
/**
* 根据条件查询单个
* @param statementId
* @param params
* @param <T>
* @return
*/
public <T> T selectOne(String statementId,Object... params) throws Exception;
/**
* 为dao接口生成代理实现类
* @param mapperClass
* @param <T>
* @return
*/
public <T> T getMapper(Class<?> mapperClass);
}
package com.learn.sqlsession;
import com.learn.pojo.Configuration;
import com.learn.pojo.MappedStatement;
import java.lang.reflect.*;
import java.util.List;
/**
* @Author liu
* @Title: DefaultSqlSession
* @ProjectName IPersistence_test
* @Description: //TODO
* @date 2020/6/19 15:21
*/
public class DefaultSqlSession implements SqlSession {
private Configuration configuration;
public DefaultSqlSession(Configuration configuration) {
this.configuration = configuration;
}
@Override
public <E> List<E> selectList(String statementId, Object... params) throws Exception {
//完成对jdbc的封装,完成对simpleExecutor里的query方法的调用
SimpleExecutor simpleExecutor = new SimpleExecutor();
MappedStatement mappedStatement = configuration.getMappedStatementMap().get(statementId);
List<E> list = simpleExecutor.query(configuration, mappedStatement, params);
return list;
}
@Override
public <T> T selectOne(String statementId, Object... params) throws Exception {
List<T> t = selectList(statementId, params);
if (t.size() == 1) {
return t.get(0);
} else {
throw new RuntimeException("查询结果为空或者返回结果过多");
}
}
@Override
public <T> T getMapper(Class<?> mapperClass) {
//使用jdk动态代理 来为dao接口生成代理对象并返回
Object proxyInstance = Proxy.newProxyInstance(DefaultSqlSession.class.getClassLoader(), new Class[]{mapperClass}, new InvocationHandler() {
@Override
public Object invoke(Object proxy, Method method, Object[] args) throws Throwable {
//底层都还是去执行jdbc代码 根据不同情况调用不同的crud方法
//准备参数 1.statmentId :sql语句的唯一标识: namespace.id
String methodName = method.getName();
String className = method.getDeclaringClass().getName();
String statmentId = className + "." + methodName;
//准备参数2 : params:args
//获取被调用方法的返回值类型
Type genericReturnType = method.getGenericReturnType();
if (genericReturnType instanceof ParameterizedType) {
List<Object> objects = selectList(statmentId, args);
return objects;
}
return selectOne(statmentId, args);
}
});
return (T) proxyInstance;
}
}
创建Executor
package com.learn.sqlsession;
import com.learn.pojo.Configuration;
import com.learn.pojo.MappedStatement;
import java.sql.SQLException;
import java.util.List;
/**
* @Author liu
* @Title: Executor
* @ProjectName IPersistence_test
* @Description: 封装jdbc
* @date 2020/6/19 15:42
*/
public interface Executor {
/**
* 查询接口
* 对jdbc进行封装
* @param configuration
* @param mappedStatement
* @param params
* @param <E>
* @return
*/
public <E> List<E> query(Configuration configuration, MappedStatement mappedStatement,Object... params) throws SQLException, Exception;
}
创建SimpleExecutor
package com.learn.sqlsession;
import com.learn.config.BoundSql;
import com.learn.pojo.Configuration;
import com.learn.pojo.MappedStatement;
import com.learn.utils.GenericTokenParser;
import com.learn.utils.ParameterMapping;
import com.learn.utils.ParameterMappingTokenHandler;
import java.beans.PropertyDescriptor;
import java.lang.reflect.Field;
import java.lang.reflect.Method;
import java.sql.Connection;
import java.sql.PreparedStatement;
import java.sql.ResultSet;
import java.sql.ResultSetMetaData;
import java.util.ArrayList;
import java.util.List;
/**
* @Author liu
* @Title: SimpleExecutor
* @ProjectName IPersistence_test
* @Description: //TODO
* @date 2020/6/19 15:46
*/
public class SimpleExecutor implements Executor {
@Override
public <E> List<E> query(Configuration configuration, MappedStatement mappedStatement, Object... params) throws Exception {
//1.注册驱动 获取数据库连接
Connection connection = configuration.getDataSource().getConnection();
// 2.获取sql语句 转换sql语句为能被jdbc能识别的语句,转换的过程中,还需要对#{}中的值进行解析存储
String sql = mappedStatement.getSql();
BoundSql boundSql = getBoundSql(sql);
// 3.获取与处理对象 preparedStatement
PreparedStatement preparedStatement = connection.prepareStatement(boundSql.getSqlText());
//4. 设置参数
//获取到参数的全路径
String paramterType = mappedStatement.getParamterType();
Class<?> paramterTypeClass = getClassType(paramterType);
List<ParameterMapping> parameterMappings = boundSql.getParameterMappings();
for (int i = 0; i < parameterMappings.size(); i++) {
ParameterMapping parameterMapping = parameterMappings.get(i);
String content = parameterMapping.getContent();
//反射 根据参数名称获取实体属性中的值 然后根据参数获取到params中具体的值
Field declaredField = paramterTypeClass.getDeclaredField(content);
//防止对象是私有的,设置暴力访问
declaredField.setAccessible(true);
Object o = declaredField.get(params[0]);
preparedStatement.setObject(i + 1, o);
}
//5.执行sql
ResultSet resultSet = preparedStatement.executeQuery();
String resultType = mappedStatement.getResultType();
Class<?> resultTypeClass = getClassType(resultType);
ArrayList<Object> objects = new ArrayList<>();
//6.封装返回结果集
while (resultSet.next()) {
Object o = resultTypeClass.newInstance();
//取出元数据 (表)
ResultSetMetaData metaData = resultSet.getMetaData();
//获取到总列数 getColumnCount
for (int i = 1; i <= metaData.getColumnCount(); i++) {
//获取到字段名 columnName下表为1开始
String columnName = metaData.getColumnName(i);
// 获取到字段的值
Object value = resultSet.getObject(columnName);
// 使用反射或者内省 根据数据库表和实体的对应关系完成封装 并生成读写方法
PropertyDescriptor propertyDescriptor = new PropertyDescriptor(columnName, resultTypeClass);
Method writeMethod = propertyDescriptor.getWriteMethod();
writeMethod.invoke(o, value);
}
objects.add(o);
}
return (List<E>) objects;
}
private Class<?> getClassType(String paramterType) throws ClassNotFoundException {
if (paramterType != null) {
Class<?> aClass = Class.forName(paramterType);
return aClass;
}
return null;
}
/**
* 完成对#{} 的解析
* 1.讲#{}使用 ? 进行代替。
* 2.解析出#{} 中的值进行存储
*
* @param sql
* @return
*/
private BoundSql getBoundSql(String sql) {
//标记处理类:配置标记解析器来完成对占位符的解析处理工作
ParameterMappingTokenHandler parameterMappingTokenHandler = new ParameterMappingTokenHandler();
GenericTokenParser genericTokenParser = new GenericTokenParser("#{", "}", parameterMappingTokenHandler);
//解析后的sql
String parseSql = genericTokenParser.parse(sql);
//#{} 中解析出来的参数名称
List<ParameterMapping> parameterMappings = parameterMappingTokenHandler.getParameterMappings();
BoundSql boundSql = new BoundSql(parseSql, parameterMappings);
return boundSql;
}
}
创建BoundSql类,用来存储转换过程中的sql语句,以及#{} 中的参数名称
package com.learn.config;
import com.learn.utils.ParameterMapping;
import java.util.ArrayList;
import java.util.List;
/**
* @Author liu
* @Title: BoundSql
* @ProjectName IPersistence_test
* @Description: 用来存储转换过程中的sql语句,以及#{} 中的参数名称
* @date 2020/6/19 16:02
*/
public class BoundSql {
/**
* 解析过后的sql
*/
private String sqlText;
private List<ParameterMapping> parameterMappings = new ArrayList<>();
public String getSqlText() {
return sqlText;
}
public void setSqlText(String sqlText) {
this.sqlText = sqlText;
}
public List<ParameterMapping> getParameterMappings() {
return parameterMappings;
}
public void setParameterMappings(List<ParameterMapping> parameterMappings) {
this.parameterMappings = parameterMappings;
}
public BoundSql(String sqlText, List<ParameterMapping> parameterMappings) {
this.sqlText = sqlText;
this.parameterMappings = parameterMappings;
}
}
好了我们的自定义持久化框架目前已经搭建完毕,具体目录结构如下图:
源码地址:https://gitee.com/FirstXiaoMaGe/custom-persistence-framework