解析MyBatis源码实现自定义持久层框架
更新时间：2022年05月28日 11:02:58 作者：第二范式
这篇文章主要介绍了手撕MyBatis源码实现自定义持久层框架,涉及到的设计模式有Builder构建者模式、⼯⼚模式、代理模式，本文通过示例代码给大家介绍的非常详细，需要的朋友可以参考下
自定义框架设计
使用端 ：
提供核⼼配置⽂件：
sqlMapConfig.xml : 存放数据源信息，引⼊mapper.xml
Mapper.xml : sql语句的配置⽂件信息
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语句的id、sql语句、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：返回值SqlSessionFactory，方法为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DefaultSqlSessionFactory
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 mappedStatementId,Object... param)：查询所有
selectOne(String mappedStatementId,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构建者模式、⼯⼚模式、代理模式
自定义框架实现
这里只做比较繁琐的查询单条和查询多条的实现，添加、修改、删除的参考自行实现。
使用端
创建sqlMapConfig.xml
<configuration>
<!--数据库配置信息-->
<dataSource>
<property name="driverClass" value="com.mysql.jdbc.Driver"></property>
<property name="jdbcUrl" value="jdbc:mysql:///learning_db"></property>
<property name="username" value="root"></property>
<property name="password" value="123456"></property>
</dataSource>
<!--存放mapper.xml的全路径-->
<mapper resource="UserMapper.xml"></mapper>
</configuration>mapper.xml
<mapper namespace="com.snf.mapper.UserMapper">
<!--sql的唯一标识：namespace.id来组成 ： mappedStatementId-->
<select id="findAll" resultType="com.snf.domain.User" >
select * from user
</select>
<!--
User user = new User()
user.setId(1);
user.setUsername("zhangsan")
-->
<select id="findByCondition" resultType="com.snf.domain.User" parameterType="com.snf.domain.User">
select * from user where id = #{id} and username = #{username}
</select>
</mapper>User实体类
public class User {
private Integer id;
private String username;
public User() {
}
public User(Integer id, String username) {
this.id = id;
this.username = 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 + '\'' +
'}';
}
}框架端
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配置类
public class Configuration {
private DataSource dataSource;
/**
* key:statementId value:封装好的mappedStatement对象
*/
private 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;
}
}MappedStatement类
public class MappedStatement {
//sql语句id
private String id;
//sql语句
private String sql;
//输入参数类型
private String parameterType;
//返回参数类型
private String resultType;
public String getId() {
return id;
}
public void setId(String id) {
this.id = id;
}
public String getSql() {
return sql;
}
public void setSql(String sql) {
this.sql = sql;
}
public String getParameterType() {
return parameterType;
}
public void setParameterType(String parameterType) {
this.parameterType = parameterType;
}
public String getResultType() {
return resultType;
}
public void setResultType(String resultType) {
this.resultType = resultType;
}
}Resources类
public class Resources {
//以流的形式读取配置文件
public static InputStream getResourceAsStream(String path){
InputStream resourceAsStream = Resources.class.getClassLoader().getResourceAsStream(path);
return resourceAsStream;
}
}SqlSessionFactoryBuilder类
public class SqlSessionFactoryBuilder {
public SqlSessionFactory build(InputStream inputStream) throws PropertyVetoException, DocumentException {
//使用dom4j解析配置文件,将解析出来的内容封装到Configuration中
XMLConfigBuilder xmlConfigBuilder = new XMLConfigBuilder();
Configuration configuration = xmlConfigBuilder.parseConfig(inputStream);
//创建sqlSessionFactory工厂对象：生产sqlSession
DefaultSqlSessionFactory defaultSqlSessionFactory = new DefaultSqlSessionFactory(configuration);
return defaultSqlSessionFactory;
}
}XMLConfigBuilder类
public class XMLConfigBuilder {
private Configuration configuration;
public XMLConfigBuilder() {
this.configuration = new Configuration();
}
/**
* 使用dom4j对配置文件进行封装,封装Configuration
*/
public Configuration parseConfig(InputStream inputStream) throws DocumentException, PropertyVetoException {
Document document = new SAXReader().read(inputStream);
Element rootElement = document.getRootElement();
List<Element> list = rootElement.selectNodes("//property");
Properties properties = new Properties();
list.forEach(element -> {
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);
//解析<Mapper>标签
List<Element> mapperList = rootElement.selectNodes("//mapper");
mapperList.stream()
.map(x -> x.attributeValue("resource"))
.map(Resources::getResourceAsStream)
.forEach(resourceAsStream -> {
XmlMapperBuilder xmlMapperBuilder = new XmlMapperBuilder(configuration);
try {
xmlMapperBuilder.parse(resourceAsStream);
} catch (DocumentException e) {
e.printStackTrace();
}
});
return configuration;
}
}XMLMapperBuilder类
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");
List<Element> list = rootElement.selectNodes("//select");
list.forEach(element -> {
String id = element.attributeValue("id");
String parameterType = element.attributeValue("parameterType");
String resultType = element.attributeValue("resultType");
String sqlText = element.getTextTrim();
MappedStatement mappedStatement = new MappedStatement();
mappedStatement.setId(id);
mappedStatement.setParameterType(parameterType);
mappedStatement.setResultType(resultType);
mappedStatement.setSql(sqlText);
String key = namespace.concat(".").concat(id);
configuration.getMappedStatementMap().put(key, mappedStatement);
});
}
}SqlSessionFactory接口及DefaultSqlSessionFactory实现类
public interface SqlSessionFactory {
SqlSession openSession();
}public class DefaultSqlSessionFactory implements SqlSessionFactory {
private Configuration configuration;
public DefaultSqlSessionFactory(Configuration configuration) {
this.configuration = configuration;
}
@Override
public SqlSession openSession() {
return new DefaultSqlSession(configuration);
}
}SqlSession接口及DefaultSqlSession实现类
public interface SqlSession {
//查询所有
<E> List<E> selectList(String mappedStatementId,Object... params) throws IllegalAccessException, IntrospectionException, InstantiationException, NoSuchFieldException, SQLException, InvocationTargetException, ClassNotFoundException;
//根据条件
<T> T selectOne(String mappedStatementId,Object... params) throws IllegalAccessException, ClassNotFoundException, IntrospectionException, InstantiationException, SQLException, InvocationTargetException, NoSuchFieldException;
//为Dao接口生成代理实现类
<T> T getMapper(Class<T> mapperClass);
}public class DefaultSqlSession implements SqlSession {
private Configuration configuration;
public DefaultSqlSession(Configuration configuration) {
this.configuration = configuration;
}
@Override
public <E> List<E> selectList(String mappedStatementId, Object... params) throws IllegalAccessException, IntrospectionException, InstantiationException, NoSuchFieldException, SQLException, InvocationTargetException, ClassNotFoundException {
SimpleExecutor simpleExecutor = new SimpleExecutor();
MappedStatement mappedStatement = configuration.getMappedStatementMap().get(mappedStatementId);
List<Object> objectList = simpleExecutor.query(configuration, mappedStatement, params);
return (List<E>) objectList;
}
@Override
public <T> T selectOne(String mappedStatementId, Object... params) throws IllegalAccessException, ClassNotFoundException, IntrospectionException, InstantiationException, SQLException, InvocationTargetException, NoSuchFieldException {
List<Object> objectList = selectList(mappedStatementId, params);
if (objectList.size() == 1) {
return (T) objectList.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<T> mapperClass) {
//使用JDK动态代理来为Dao接口生成代理对象,并返回
return (T) Proxy.newProxyInstance(DefaultSqlSession.class.getClassLoader(), new Class[]{mapperClass}, ((proxy, method, args) -> {
String methodName = method.getName();
String className = method.getDeclaringClass().getName();
String mappedStatementId = className.concat(".").concat(methodName);
//获取被调用方法的返回值类型
Type genericReturnType = method.getGenericReturnType();
//判断是否进行了泛型类型参数化
if (genericReturnType instanceof ParameterizedType){
List<Object> objectList = selectList(mappedStatementId, args);
return objectList;
}
return selectOne(mappedStatementId,args);
}));
}
}Executor接口及SimpleExecutor实现类
public interface Executor {
<E>List<E> query(Configuration configuration, MappedStatement mappedStatement,Object... params) throws SQLException, IntrospectionException, InvocationTargetException, IllegalAccessException, InstantiationException, ClassNotFoundException, NoSuchFieldException;
}public class SimpleExecutor implements Executor {
@Override
public <E> List<E> query(Configuration configuration, MappedStatement mappedStatement, Object... params) throws SQLException, IntrospectionException, InvocationTargetException, IllegalAccessException, InstantiationException, ClassNotFoundException, NoSuchFieldException {
//注册驱动,获取连接
Connection connection = configuration.getDataSource().getConnection();
//获取sql语句：select * from user where id = #{id} and username = #{username}
//转换sql语句：select * from user where id = ? and username = ?
//转换的过程中,还需要对#{}里面的参数名称进行解析存储
String sql = mappedStatement.getSql();
BoundSql boundSql = getBoundSql(sql);
//获取预处理对象：preparedStatement
PreparedStatement preparedStatement = connection.prepareStatement(boundSql.getSqlText());
//设置参数
//获取到了参数的全路径
String parameterType = mappedStatement.getParameterType();
Class<?> parameterTypeClass = getClassType(parameterType);
List<ParameterMapping> parameterMappingList = boundSql.getParameterMappingList();
for (int i = 0; i < parameterMappingList.size(); i++) {
ParameterMapping parameterMapping = parameterMappingList.get(i);
String content = parameterMapping.getContent();
//反射
Field declaredField = parameterTypeClass.getDeclaredField(content);
//暴力访问
declaredField.setAccessible(true);
Object o = declaredField.get(params[0]);
preparedStatement.setObject(i + 1, o);
}
//执行sql
ResultSet resultSet = preparedStatement.executeQuery();
String resultType = mappedStatement.getResultType();
Class<?> resultTypeClass = getClassType(resultType);
List<Object> objectList = new ArrayList<>();
//封装返回结果集
while (resultSet.next()) {
Object o = resultTypeClass.newInstance();
//元数据
ResultSetMetaData metaData = resultSet.getMetaData();
for (int i = 1; i <= metaData.getColumnCount(); i++) {
// 字段名
String columnName = metaData.getColumnName(i);
// 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
PropertyDescriptor propertyDescriptor = new PropertyDescriptor(columnName, resultTypeClass);
Method writeMethod = propertyDescriptor.getWriteMethod();
writeMethod.invoke(o, value);
}
objectList.add(o);
}
return (List<E>) objectList;
}
private Class<?> getClassType(String paramterType) throws ClassNotFoundException {
if (paramterType != null) {
Class<?> aClass = Class.forName(paramterType);
return aClass;
}
return null;
}
/**
* 完成对#{}的解析工作
* 1.将#{}使用?进行代替
* 2.解析出#{}里面的字段名进行存储
*
* @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);
//解析出来的sql
String parseSql = genericTokenParser.parse(sql);
//#{}里面解析出来的参数名称
List<ParameterMapping> parameterMappings = parameterMappingTokenHandler.getParameterMappings();
BoundSql boundSql = new BoundSql(parseSql, parameterMappings);
return boundSql;
}
}BoundSql类
public class BoundSql {
private String sqlText; //解析过后的sql
private List<ParameterMapping> parameterMappingList = new ArrayList<>();
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;
}
}GenericTokenParser、ParameterMapping、TokenHandler、ParameterMappingTokenHandler工具类
GenericTokenParser：解析${}或#{}中的参数名称
ParameterMapping：存储${}或#{}中的参数名称
TokenHandler：替换${}或#{}处理接口
ParameterMappingTokenHandler：替换${}或#{}处理接口的实现类
public class GenericTokenParser {
private final String openToken; //开始标记
private final String closeToken; //结束标记
private final TokenHandler handler; //标记处理器
public GenericTokenParser(String openToken, String closeToken, TokenHandler handler) {
this.openToken = openToken;
this.closeToken = closeToken;
this.handler = handler;
}
/**
* 解析${}和#{}
* @param text
* @return
* 该方法主要实现了配置文件、脚本等片段中占位符的解析、处理工作，并返回最终需要的数据。
* 其中，解析工作由该方法完成，处理工作是由处理器handler的handleToken()方法来实现
*/
public String parse(String text) {
// 验证参数问题，如果是null，就返回空字符串。
if (text == null || text.isEmpty()) {
return "";
}
// 下面继续验证是否包含开始标签，如果不包含，默认不是占位符，直接原样返回即可，否则继续执行。
int start = text.indexOf(openToken, 0);
if (start == -1) {
return text;
}
// 把text转成字符数组src，并且定义默认偏移量offset=0、存储最终需要返回字符串的变量builder，
// text变量中占位符对应的变量名expression。判断start是否大于-1(即text中是否存在openToken)，如果存在就执行下面代码
char[] src = text.toCharArray();
int offset = 0;
final StringBuilder builder = new StringBuilder();
StringBuilder expression = null;
while (start > -1) {
// 判断如果开始标记前如果有转义字符，就不作为openToken进行处理，否则继续处理
if (start > 0 && src[start - 1] == '\\') {
builder.append(src, offset, start - offset - 1).append(openToken);
offset = start + openToken.length();
} else {
//重置expression变量，避免空指针或者老数据干扰。
if (expression == null) {
expression = new StringBuilder();
} else {
expression.setLength(0);
}
builder.append(src, offset, start - offset);
offset = start + openToken.length();
int end = text.indexOf(closeToken, offset);
while (end > -1) {////存在结束标记时
if (end > offset && src[end - 1] == '\\') {//如果结束标记前面有转义字符时
// this close token is escaped. remove the backslash and continue.
expression.append(src, offset, end - offset - 1).append(closeToken);
offset = end + closeToken.length();
end = text.indexOf(closeToken, offset);
} else {//不存在转义字符，即需要作为参数进行处理
expression.append(src, offset, end - offset);
offset = end + closeToken.length();
break;
}
}
if (end == -1) {
// close token was not found.
builder.append(src, start, src.length - start);
offset = src.length;
} else {
//首先根据参数的key（即expression）进行参数处理，返回?作为占位符
builder.append(handler.handleToken(expression.toString()));
offset = end + closeToken.length();
}
}
start = text.indexOf(openToken, offset);
}
if (offset < src.length) {
builder.append(src, offset, src.length - offset);
}
return builder.toString();
}
}public class ParameterMapping {
private String content;
public ParameterMapping(String content) {
this.content = content;
}
public String getContent() {
return content;
}
public void setContent(String content) {
this.content = content;
}
}public interface TokenHandler {
String handleToken(String content);
}public class ParameterMappingTokenHandler implements TokenHandler {
private List<ParameterMapping> parameterMappings = new ArrayList<>();
// context是参数名称 #{id} #{username}
public String handleToken(String content) {
parameterMappings.add(buildParameterMapping(content));
return "?";
}
private ParameterMapping buildParameterMapping(String content) {
ParameterMapping parameterMapping = new ParameterMapping(content);
return parameterMapping;
}
public List<ParameterMapping> getParameterMappings() {
return parameterMappings;
}
public void setParameterMappings(List<ParameterMapping> parameterMappings) {
this.parameterMappings = parameterMappings;
}
}到此这篇关于手撕MyBatis源码实现自定义持久层框架的文章就介绍到这了,更多相关MyBatis自定义持久层框架内容请搜索脚本之家以前的文章或继续浏览下面的相关文章希望大家以后多多支持脚本之家！
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