自定義mybatis持久層框架

1.1 分析JDBC操作問題

public static void main(String[] args) {
 Connection connection = null;
 PreparedStatement preparedStatement = null;
 ResultSet resultSet = null;
 try {
 // 加載數據庫驅動
 Class.forName("com.mysql.jdbc.Driver");
 // 通過驅動管理類獲取數據庫鏈接
 connection =
DriverManager.getConnection("jdbc:mysql://localhost:3306/mybatis?
characterEncoding=utf-8", "root", "root");
 // 定義sql語句？表示佔位符
 String sql = "select * from user where username = ?";
 // 獲取預處理statement
 preparedStatement = connection.prepareStatement(sql);
 // 設置參數，第⼀個參數爲sql語句中參數的序號(從1開始)，第⼆個參數爲設置的參數值
preparedStatement.setString(1, "tom");
 // 向數據庫發出sql執⾏查詢，查詢出結果集
 resultSet = preparedStatement.executeQuery();
 // 遍歷查詢結果集
 while (resultSet.next()) {
 int id = resultSet.getInt("id");
 String username = resultSet.getString("username");
 // 封裝User
 user.setId(id);
 user.setUsername(username);
 }
 System.out.println(user);
 }
 } catch (Exception e) {
 e.printStackTrace();
 } finally {
 // 釋放資源
 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問題總結：

原始jdbc開發存在的問題如下：

1、 數據庫連接創建、釋放頻繁造成系統資源浪費，從⽽影響系統性能。

2、 Sql語句在代碼中硬編碼，造成代碼不易維護，實際應⽤中sql變化的可能較⼤，sql變動需要改變

java代碼。

3、 使⽤preparedStatement向佔有位符號傳參數存在硬編碼，因爲sql語句的where條件不⼀定，可能

多也可能少，修改sql還要修改代碼，系統不易維護。

4、 對結果集解析存在硬編碼(查詢列名)，sql變化導致解析代碼變化，系統不易維護，如果能將數據 庫

記錄封裝成pojo對象解析⽐較⽅便

 

1.2 問題解決思路

①使⽤數據庫連接池初始化連接資源

②將sql語句抽取到xml配置⽂件中

③使⽤反射、內省等底層技術，⾃動將實體與表進⾏屬性與字段的⾃動映射

1.3 ⾃定義框架設計

使⽤端：

提供核⼼配置⽂件：

sqlMapConfig.xml : 存放數據源信息，引⼊mapper.xml

Mapper.xml : sql語句的配置⽂件信息

框架端：

1.讀取配置⽂件

讀取完成以後以流的形式存在，我們不能將讀取到的配置信息以流的形式存放在內存中，不好操作，可

以創建javaBean來存儲

（1）Configuration : 存放數據庫基本信息、Map<唯⼀標識，Mapper> 唯⼀標識：namespace + "."

+ id

（2）MappedStatement：sql語句、statement類型、輸⼊參數java類型、輸出參數java類型

2.解析配置⽂件

創建sqlSessionFactoryBuilder類：

⽅法：sqlSessionFactory build()：

第⼀：使⽤dom4j解析配置⽂件，將解析出來的內容封裝到Configuration和MappedStatement中

第⼆：創建SqlSessionFactory的實現類DefaultSqlSession

3.創建SqlSessionFactory：

⽅法：openSession() : 獲取sqlSession接⼝的實現類實例對象

4.創建sqlSession接⼝及實現類：主要封裝crud⽅法

⽅法：selectList(String statementId,Object param)：查詢所有

selectOne(String statementId,Object param)：查詢單個

具體實現：封裝JDBC完成對數據庫表的查詢操作

涉及到的設計模式：

Builder構建者設計模式、⼯⼚模式、代理模式

 

1.4 ⾃定義框架實現

在使⽤端項⽬中創建配置配置⽂件

創建 sqlMapConfig.xml〈configuration〉

<!--數據庫連接信息-->
<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.xml"></mapper>
</configuration>
mapper.xml
<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實體

public class User {
//主鍵標識
private Integer id;
//⽤戶名
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;
}
@Override
public String toString() {
return "User{" +
"id=" + id + ", username='" + username + '\'' + '}';
}
}

 

再創建⼀個Maven⼦⼯程並且導⼊需要⽤到的依賴座標

<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 {
//數據源
private DataSource dataSource;
//map集合： key:statementId value:MappedStatement
private 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 {
//id
private Integer id;
//sql語句
private String sql;
//輸⼊參數
private Class<?> paramterType;
//輸出參數
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) throws
DocumentException, PropertyVetoException, ClassNotFoundException {
//1.解析配置⽂件，封裝Configuration XMLConfigerBuilder
xmlConfigerBuilder = new
XMLConfigerBuilder(configuration);
Configuration configuration =
xmlConfigerBuilder.parseConfiguration(inputStream);
//2.創建 sqlSessionFactory
SqlSessionFactory sqlSessionFactory = new
DefaultSqlSessionFactory(configuration);
return sqlSessionFactory;
}
XMLConfigerBuilder
public class XMLConfigerBuilder { private Configuration configuration;
public XMLConfigerBuilder(Configuration configuration) {
this.configuration = new Configuration();
}
public Configuration parseConfiguration(InputStream inputStream) throws
DocumentException, 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);
}
//連接池
ComboPooledDataSource comboPooledDataSource = new
ComboPooledDataSource();
 
comboPooledDataSource.setDriverClass(properties.getProperty("driverClass"));
comboPooledDataSource.setJdbcUrl(properties.getProperty("jdbcUrl"));
comboPooledDataSource.setUser(properties.getProperty("username"));
comboPooledDataSource.setPassword(properties.getProperty("password"));
//填充 configuration
configuration.setDataSource(comboPooledDataSource);
//mapper 部分
List<Element> mapperElements = rootElement.selectNodes("//mapper");
XMLMapperBuilder xmlMapperBuilder = new
XMLMapperBuilder(configuration);
for (Element mapperElement : mapperElements) {
String mapperPath = mapperElement.attributeValue("resource");
InputStream resourceAsSteam =
Resources.getResourceAsSteam(mapperPath);
xmlMapperBuilder.parse(resourceAsSteam);
}
return configuration;
}
XMLMapperBuilder
public class XMLMapperBuilder {
private Configuration configuration;
public XMLMapperBuilder(Configuration configuration) { 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"); //輸⼊參
數class
Class<?> paramterTypeClass = getClassType(paramterType);
//返回結果class
Class<?> resultTypeClass = getClassType(resultType);
//statementId
String key = namespace + "." + id;
//sql語句
String textTrim = element.getTextTrim();
//封裝 mappedStatement
MappedStatement mappedStatement = new MappedStatement();
mappedStatement.setId(id);
mappedStatement.setParamterType(paramterTypeClass);
mappedStatement.setResultType(resultTypeClass);
mappedStatement.setSql(textTrim);
//填充 configuration
configuration.getMappedStatementMap().put(key, mappedStatement);
private Class<?> getClassType (String paramterType) throws
ClassNotFoundException {
Class<?> aClass = Class.forName(paramterType);
return aClass;
}
}
sqlSessionFactory 接⼝及D efaultSqlSessionFactory 實現類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 實現類
public interface SqlSession {
public <E> List<E> selectList(String statementId, Object... param)
Exception;
public <T> T selectOne(String statementId,Object... params) throws
Exception;
public void close() throws SQLException;
}
public class DefaultSqlSession implements SqlSession {
private Configuration configuration;
public DefaultSqlSession(Configuration configuration) {
this.configuration = configuration;
//處理器對象
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 中調⽤ selectList
public <T > T selectOne(String statementId, Object...params) throws
Exception {
List<Object> objects = selectList(statementId, params);
if (objects.size() == 1) {
return (T) objects.get(0);
} else {
throw new RuntimeException("返回結果過多");
} }
public void close () throws SQLException {
simpleExcutor.close();
}
}

 

Executor

public interface Executor {
<E> List<E> query(Configuration configuration, MappedStatement
mappedStatement,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, MappedStatement
mappedStatement, Object[] param) throws SQLException, NoSuchFieldException,
IllegalAccessException, InstantiationException, IntrospectionException,
InvocationTargetException {
//獲取連接
connection = configuration.getDataSource().getConnection();
// select * from user where id = #{id} and username = #{username}
String sql = mappedStatement.getSql();
//對sql進⾏處理
BoundSql boundsql = getBoundSql(sql);
// select * from where id = ? and username = ?
String finalSql = boundsql.getSqlText();
//獲取傳⼊參數類型
Class<?> paramterType = mappedStatement.getParamterType();
//獲取預編譯preparedStatement對象
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);
//參數的值
Object o = declaredField.get(param[0]); //給佔位符賦值
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++) {
//屬性名
String columnName = metaData.getColumnName(i);
//屬性值
Object value = resultSet.getObject(columnName);
//創建屬性描述器，爲屬性⽣成讀寫⽅法
PropertyDescriptor propertyDescriptor = new
PropertyDescriptor(columnName, resultType);
//獲取寫⽅法
Method writeMethod = propertyDescriptor.getWriteMethod();
//向類中寫⼊值
writeMethod.invoke(o, value);
}
results.add(o);
}
return results;
}
@Override
public void close() throws SQLException {
connection.close();
}
private BoundSql getBoundSql(String sql) {
//標記處理類：主要是配合通⽤標記解析器GenericTokenParser類完成對配置⽂件等的解
析⼯作，其中TokenHandler主要完成處理
ParameterMappingTokenHandler parameterMappingTokenHandler = new
ParameterMappingTokenHandler();
//GenericTokenParser :通⽤的標記解析器，完成了代碼⽚段中的佔位符的解析，然後再根
據給定的標記處理器(TokenHandler)來進⾏表達式的處理
//三個參數：分別爲openToken (開始標記)、closeToken (結束標記)、handler (標記
處 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 ⾃定義框架優化

通過上述我們的⾃定義框架，我們解決了JDBC操作數據庫帶來的⼀些問題：例如頻繁創建釋放數據庫連

接，硬編碼，⼿動封裝返回結果集等問題，但是現在我們繼續來分析剛剛完成的⾃定義框架代碼，有沒

有什麼問題？

問題如下：

dao的實現類中存在重複的代碼，整個操作的過程模板重複(創建sqlsession,調⽤sqlsession⽅

法，關閉 sqlsession)

dao的實現類中存在硬編碼，調⽤sqlsession的⽅法時，參數statement的id硬編碼

}

}

public class BoundSql {

//解析過後的sql語句

private String sqlText;

//解析出來的參數

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;

}

}解決：使⽤代理模式來創建接⼝的代理對象

@Test

public void test2() throws Exception {

InputStream resourceAsSteam = Resources.getResourceAsSteam(path：

"sqlMapConfig.xml")

SqlSessionFactory build = new

SqlSessionFactoryBuilder().build(resourceAsSteam);

SqlSession sqlSession = build.openSession();

User user = new User();

user.setld(l);

user.setUsername("tom");

//代理對象

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);

實現類

@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<> ();

//判斷是否實現泛型類型參數化

if(genericReturnType instanceof ParameterizedType){

return selectList(key,args);

return selectOne(key,args);

}

});