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这篇“MyBatis如何实现自定义持久层框架”文章的知识点大部分人都不太理解，所以小编给大家总结了以下内容，内容详细，步骤清晰，具有一定的借鉴价值，希望大家阅读完这篇文章能有所收获，下面我们一起来看看这篇“MyBatis如何实现自定义持久层框架”文章吧。
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
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。
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 + '\'' +
'}';
}
}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;
}
}以上就是关于“MyBatis如何实现自定义持久层框架”这篇文章的内容，相信大家都有了一定的了解，希望小编分享的内容对大家有帮助，若想了解更多相关的知识内容，请关注亿速云行业资讯频道。
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