自定义mybatis持久层框架

1.1 分析JDBC操作问题

public static void main(String[] args) { Connection connection = null; PreparedStatement preparedStatement = null; ResultSet resultSet = null; try { // 加载数据库驱动 Class.forName("com.mysql.jdbc.Driver"); // 通过驱动管理类获取数据库链接 connection =DriverManager.getConnection("jdbc:mysql://localhost:3306/mybatis?characterEncoding=utf-8", "root", "root"); // 定义sql语句？表示占位符 String sql = "select * from user where username = ?"; // 获取预处理statement preparedStatement = connection.prepareStatement(sql); // 设置参数，第⼀个参数为sql语句中参数的序号(从1开始)，第⼆个参数为设置的参数值preparedStatement.setString(1, "tom"); // 向数据库发出sql执⾏查询，查询出结果集 resultSet = preparedStatement.executeQuery(); // 遍历查询结果集 while (resultSet.next()) { int id = resultSet.getInt("id"); String username = resultSet.getString("username"); // 封装User user.setId(id); user.setUsername(username); } System.out.println(user); } } catch (Exception e) { e.printStackTrace(); } finally { // 释放资源 if (resultSet != null) { try { resultSet.close(); } catch (SQLException e) { e.printStackTrace();if (preparedStatement != null) {try {preparedStatement.close();} catch (SQLException e) {e.printStackTrace();}}if (connection != null) {try {connection.close();} catch (SQLException e) {e.printStackTrace();}}}

 

JDBC问题总结：
原始jdbc开发存在的问题如下：
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。
2、 Sql语句在代码中硬编码，造成代码不易维护，实际应⽤中sql变化的可能较⼤，sql变动需要改变
java代码。
3、 使⽤preparedStatement向占有位符号传参数存在硬编码，因为sql语句的where条件不⼀定，可能
多也可能少，修改sql还要修改代码，系统不易维护。
4、 对结果集解析存在硬编码(查询列名)，sql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
 
1.2 问题解决思路
①使⽤数据库连接池初始化连接资源
②将sql语句抽取到③使⽤反射、内省等底层技术，⾃动将实体与表进⾏属性与字段的⾃动映射
1.3 ⾃定义框架设计
使⽤端：
提供核⼼配置⽂件：
sqlMapConfig.Mapper.框架端：
1.读取配置⽂件
读取完成以后以流的形式存在，我们不能将读取到的配置信息以流的形式存放在内存中，不好操作，可
以创建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
2.解析配置⽂件
创建sqlSessionFactoryBuilder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DefaultSqlSession
3.创建SqlSessionFactory：
⽅法：openSession() : 获取sqlSession接⼝的实现类实例对象
4.创建sqlSession接⼝及实现类：主要封装crud⽅法
⽅法：selectList(String statementId,Object param)：查询所有
selectOne(String statementId,Object param)：查询单个
具体实现：封装JDBC完成对数据库表的查询操作
涉及到的设计模式：
Builder构建者设计模式、⼯⼚模式、代理模式
 
1.4 ⾃定义框架实现
在使⽤端项⽬中创建配置配置⽂件
创建 sqlMapConfig.

<!--数据库连接信息--><property name="driverClass" value="com.mysql.jdbc.Driver"></property><property name="jdbcUrl" value="jdbc:mysql:///zdy_mybatis"></property><property name="user" value="root"></property><property name="password" value="root"></property><! --引⼊sql配置信息--><mapper resource="mapper.mapper.<mapper namespace="User"><select id="selectOne" paramterType="com.lagou.pojo.User"resultType="com.lagou.pojo.User">select * from user where id = #{id} and username =#{username}</select> <select id="selectList" resultType="com.lagou.pojo.User">select * from user</select></mapper>

 

User实体

public class User {//主键标识private Integer id;//⽤户名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;}@Overridepublic String toString() {return "User{" +"id=" + id + ", username='" + username + '\'' + '}';}}

 

再创建⼀个Maven⼦⼯程并且导⼊需要⽤到的依赖坐标

<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>

 

Configuration

public class Configuration {//数据源private DataSource dataSource;//map集合： key:statementId value:MappedStatementprivate Map<String,MappedStatement> mappedStatementMap = new HashMap<String,MappedStatement>();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;}}

 

MappedStatement

public class MappedStatement {//idprivate Integer id;//sql语句private String sql;//输⼊参数private Class<?> paramterType;//输出参数private Class<?> resultType;public Integer getId() {return id;}public void setId(Integer id) {this.id = id;}public String getSql() {return sql;}public void setSql(String sql) {this.sql = sql; }public Class<?> getParamterType() {return paramterType;}public void setParamterType(Class<?> paramterType) {this.paramterType = paramterType;}public Class<?> getResultType() {return resultType;}public void setResultType(Class<?> resultType) {this.resultType = resultType;}}

 

Resources

public class Resources {　　public static InputStream getResourceAsSteam(String path){ 
　　InputStream resourceAsStream = Resources.class.getClassLoader.getResourceAsStream(path);　　return resourceAsStream;　　}}

 

SqlSessionFactoryBuilder

public class SqlSessionFactoryBuilder {private Configuration configuration;public SqlSessionFactoryBuilder() {this.configuration = new Configuration();}public SqlSessionFactory build(InputStream inputStream) throwsDocumentException, PropertyVetoException, ClassNotFoundException {//1.解析配置⽂件，封装Configuration new=//2.创建 sqlSessionFactorySqlSessionFactory sqlSessionFactory = newDefaultSqlSessionFactory(configuration);return sqlSessionFactory;}public class private Configuration configuration;public this.configuration = new Configuration();}public Configuration parseConfiguration(InputStream inputStream) throwsDocumentException, PropertyVetoException, ClassNotFoundException {Document document = new SAXReader().read(inputStream);//<configuation>Element rootElement = document.getRootElement();List<Element> propertyElements =rootElement.selectNodes("//property");Properties properties = new Properties();for (Element propertyElement : propertyElements) {String name = propertyElement.attributeValue("name");String value = propertyElement.attributeValue("value");properties.setProperty(name,value);}//连接池ComboPooledDataSource comboPooledDataSource = newComboPooledDataSource(); comboPooledDataSource.setDriverClass(properties.getProperty("driverClass"));comboPooledDataSource.setJdbcUrl(properties.getProperty("jdbcUrl"));comboPooledDataSource.setUser(properties.getProperty("username"));comboPooledDataSource.setPassword(properties.getProperty("password"));//填充 configurationconfiguration.setDataSource(comboPooledDataSource);//mapper 部分List<Element> mapperElements = rootElement.selectNodes("//mapper");= newfor (Element mapperElement : mapperElements) {String mapperPath = mapperElement.attributeValue("resource");InputStream resourceAsSteam =Resources.getResourceAsSteam(mapperPath);return configuration;}public class private Configuration configuration;public this.configuration = configuration;}public void parse(InputStream inputStream) throws DocumentException,ClassNotFoundException {Document document = new SAXReader().read(inputStream);Element rootElement = document.getRootElement();String namespace = rootElement.attributeValue("namespace");List<Element> select = rootElement.selectNodes("select");for (Element element : select) { //id的值String id = element.attributeValue("id");String paramterType = element.attributeValue("paramterType");String resultType = element.attributeValue("resultType"); //输⼊参数classClass<?> paramterTypeClass = getClassType(paramterType);//返回结果classClass<?> resultTypeClass = getClassType(resultType);//statementIdString key = namespace + "." + id;//sql语句String textTrim = element.getTextTrim();//封装 mappedStatementMappedStatement mappedStatement = new MappedStatement();mappedStatement.setId(id);mappedStatement.setParamterType(paramterTypeClass);mappedStatement.setResultType(resultTypeClass);mappedStatement.setSql(textTrim);//填充 configurationconfiguration.getMappedStatementMap().put(key, mappedStatement);private Class<?> getClassType (String paramterType) throwsClassNotFoundException {Class<?> aClass = Class.forName(paramterType);return aClass;}}sqlSessionFactory 接⼝及D efaultSqlSessionFactory 实现类public interface SqlSessionFactory {public SqlSession openSession();}public class DefaultSqlSessionFactory implements SqlSessionFactory {private Configuration configuration;public DefaultSqlSessionFactory(Configuration configuration) {this.configuration = configuration;}public SqlSession openSession(){return new DefaultSqlSession(configuration);}}sqlSession 接⼝及 DefaultSqlSession 实现类public interface SqlSession {public <E> List<E> selectList(String statementId, Object... param)Exception;public <T> T selectOne(String statementId,Object... params) throwsException;public void close() throws SQLException;}public class DefaultSqlSession implements SqlSession {private Configuration configuration;public DefaultSqlSession(Configuration configuration) {this.configuration = configuration;//处理器对象private Executor simpleExcutor = new SimpleExecutor();public <E > List < E > selectList(String statementId, Object...param)throws Exception {MappedStatement mappedStatement =configuration.getMappedStatementMap().get(statementId);List<E> query = simpleExcutor.query(configuration,mappedStatement, param);return query;}//selectOne 中调⽤ selectListpublic <T > T selectOne(String statementId, Object...params) throwsException {List<Object> objects = selectList(statementId, params);if (objects.size() == 1) {return (T) objects.get(0);} else {throw new RuntimeException("返回结果过多");} }public void close () throws SQLException {simpleExcutor.close();}}

 

Executor

public interface Executor {<E> List<E> query(Configuration configuration, MappedStatementmappedStatement,Object[] param) throws Exception;void close() throws SQLException;}

 

SimpleExecutor

public class SimpleExecutor implements Executor {private Connection connection = null;public <E> List<E> query(Configuration configuration, MappedStatementmappedStatement, Object[] param) throws SQLException, NoSuchFieldException,IllegalAccessException, InstantiationException, IntrospectionException,InvocationTargetException {//获取连接connection = configuration.getDataSource().getConnection();// select * from user where id = #{id} and username = #{username}String sql = mappedStatement.getSql();//对sql进⾏处理BoundSql boundsql = getBoundSql(sql);// select * from where id = ? and username = ?String finalSql = boundsql.getSqlText();//获取传⼊参数类型Class<?> paramterType = mappedStatement.getParamterType();//获取预编译preparedStatement对象PreparedStatement preparedStatement =connection.prepareStatement(finalSql);List<ParameterMapping> parameterMappingList =boundsql.getParameterMappingList();for (int i = 0; i < parameterMappingList.size(); i++) {ParameterMapping parameterMapping = parameterMappingList.get(i);String name = parameterMapping.getName();//反射Field declaredField = paramterType.getDeclaredField(name);declaredField.setAccessible(true);//参数的值Object o = declaredField.get(param[0]); //给占位符赋值preparedStatement.setObject(i + 1, o);}ResultSet resultSet = preparedStatement.executeQuery();Class<?> resultType = mappedStatement.getResultType();ArrayList<E> results = new ArrayList<E>();while (resultSet.next()) {ResultSetMetaData metaData = resultSet.getMetaData();(E) resultType.newInstance();int columnCount = metaData.getColumnCount();for (int i = 1; i <= columnCount; i++) {//属性名String columnName = metaData.getColumnName(i);//属性值Object value = resultSet.getObject(columnName);//创建属性描述器，为属性⽣成读写⽅法PropertyDescriptor propertyDescriptor = newPropertyDescriptor(columnName, resultType);//获取写⽅法Method writeMethod = propertyDescriptor.getWriteMethod();//向类中写⼊值writeMethod.invoke(o, value);}results.add(o);}return results;}@Overridepublic void close() throws SQLException {connection.close();}private BoundSql getBoundSql(String sql) {//标记处理类：主要是配合通⽤标记解析器GenericTokenParser类完成对配置⽂件等的解析⼯作，其中TokenHandler主要完成处理ParameterMappingTokenHandler parameterMappingTokenHandler = newParameterMappingTokenHandler();//GenericTokenParser :通⽤的标记解析器，完成了代码⽚段中的占位符的解析，然后再根据给定的标记处理器(TokenHandler)来进⾏表达式的处理//三个参数：分别为openToken (开始标记)、closeToken (结束标记)、handler (标记处 理器)GenericTokenParser genericTokenParser = new GenericTokenParser("# {","}", parameterMappingTokenHandler);String parse = genericTokenParser.parse(sql);List<ParameterMapping> parameterMappings =parameterMappingTokenHandler.getParameterMappings();BoundSql boundSql = new BoundSql(parse, parameterMappings);return boundSql;BoundSql

 

1.5 ⾃定义框架优化
通过上述我们的⾃定义框架，我们解决了JDBC操作数据库带来的⼀些问题：例如频繁创建释放数据库连
接，硬编码，⼿动封装返回结果集等问题，但是现在我们继续来分析刚刚完成的⾃定义框架代码，有没
有什么问题？
问题如下：
dao的实现类中存在重复的代码，整个操作的过程模板重复(创建sqlsession,调⽤sqlsession⽅
法，关闭 sqlsession)
dao的实现类中存在硬编码，调⽤sqlsession的⽅法时，参数statement的id硬编码
}
}
public class BoundSql {
//解析过后的sql语句
private String sqlText;
//解析出来的参数
private List<ParameterMapping> parameterMappingList = new
ArrayList<ParameterMapping>();
public BoundSql(String sqlText, List<ParameterMapping>
parameterMappingList) {
this.sqlText = sqlText;
this.parameterMappingList = parameterMappingList;
}
public String getSqlText() {
return sqlText;
}
public void setSqlText(String sqlText) {
this.sqlText = sqlText;
}
public List<ParameterMapping> getParameterMappingList() {
return parameterMappingList;
}
public void setParameterMappingList(List<ParameterMapping>
parameterMappingList) {
this.parameterMappingList = parameterMappingList;
}
}解决：使⽤代理模式来创建接⼝的代理对象
@Test
public void test2() throws Exception {
InputStream resourceAsSteam = Resources.getResourceAsSteam(path：
"sqlMapConfig.SqlSessionFactory build = new
SqlSessionFactoryBuilder().build(resourceAsSteam);
SqlSession sqlSession = build.openSession();
User user = new User();
user.setld(l);
user.setUsername("tom");
//代理对象
UserMapper userMapper = sqlSession.getMappper(UserMapper.class);
User userl = userMapper.selectOne(user);
System・out.println(userl);
}
在sqlSession中添加⽅法
public interface SqlSession {
public <T> T getMappper(Class<?> mapperClass);
实现类
@Override
public <T> T getMappper(Class<?> mapperClass) {
T o = (T) Proxy.newProxyInstance(mapperClass.getClassLoader(), new
Class[] {mapperClass}, new InvocationHandler() {
@Override
public Object invoke(Object proxy, Method method, Object[] args)
throws Throwable {
// selectOne
String methodName = method.getName();
// className:namespace
String className = method.getDeclaringClass().getName();
//statementid
String key = className+"."+methodName;
MappedStatement mappedStatement =
configuration.getMappedStatementMap().get(key);
Type genericReturnType = method.getGenericReturnType();
ArrayList arrayList = new ArrayList<> ();
//判断是否实现泛型类型参数化
if(genericReturnType instanceof ParameterizedType){
return selectList(key,args);
return selectOne(key,args);
}
});
 

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1.1分析JDBC操作问题publicstaticvoidmain(String[]args){Connectionconnection=null;PreparedStatementpreparedStatement=null;ResultSetresultSet=null;try{//加载数据库驱动Class.forName("com.mysql.jdbc.Driver");
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