手写mybatis核心流程代码demo

package com.kkb.mybatis.test; import java.io.InputStream; import java.lang.reflect.Field; import java.sql.Connection; import java.sql.PreparedStatement; import java.sql.ResultSet; import java.sql.ResultSetMetaData; import java.sql.SQLException; import java.util.ArrayList; import java.util.List; import java.util.Properties; import javax.sql.DataSource; import org.apache.commons.dbcp.BasicDataSource; import org.dom4j.Document; import org.dom4j.Element; import org.dom4j.io.SAXReader; import org.junit.Test; import com.kkb.mybatis.framework.config.Configuration; import com.kkb.mybatis.framework.config.MappedStatement; import com.kkb.mybatis.framework.sqlsource.BoundSql; import com.kkb.mybatis.framework.sqlsource.ParameterMapping; import com.kkb.mybatis.framework.sqlsource.iface.SqlSource; import com.kkb.mybatis.po.User; import com.kkb.mybatis.utils.SimpleTypeRegistry; /** * 目的是使用XML来表达mybatis的全局配置信息，和业务相关的SQL映射信息 (映射文件) 其次，优化数据连接的创建（使用连接池） * * @author 灭霸詹 * */ public class MybatisV2 { /** * 封装了全局配置文件和映射文件中的所有信息 */ private Configuration configuration = new Configuration(); private String namespace; @Test public void test() { loadConfiguration(); User user = new User(); user.setUsername("王五"); List<User> users = selectList("queryUserById", user); System.out.println(users); } private void loadConfiguration() { // 指定全局配置文件的路径 String location = "mybatis-config.xml"; // 获取对应的InputStream对象 InputStream inputStream = getInputStream(location); // 获取Document对象 Document document = createDocument(inputStream); // 按照全局配置文件和映射文件的XML语义进行解析 loadConfigurationElement(document.getRootElement()); } /** * * @param rootElement * <configuration> */ private void loadConfigurationElement(Element rootElement) { Element environments = rootElement.element("environments"); parseEnvironments(environments); Element mappers = rootElement.element("mappers"); parseMappers(mappers); } /** * * @param mappers * <mappers> */ @SuppressWarnings("unchecked") private void parseMappers(Element mappers) { List<Element> mapperElements = mappers.elements("mapper"); for (Element mapperElement : mapperElements) { parseMapper(mapperElement); } } private void parseMapper(Element mapperElement) { String resource = mapperElement.attributeValue("resource"); InputStream inputStream = this.getClass().getClassLoader().getResourceAsStream(resource); Document document = createDocument(inputStream); // 按照映射文件的语义进行解析 parseXmlMapper(document.getRootElement()); } @SuppressWarnings("unchecked") private void parseXmlMapper(Element rootElement) { // 为了方便管理statement，需要使用statement唯一标识 namespace = rootElement.attributeValue("namespace"); List<Element> selectElements = rootElement.elements("select"); for (Element selectElement : selectElements) { parseStatementElement(selectElement); } } private void parseStatementElement(Element selectElement) { String statementId = selectElement.attributeValue("id"); if (statementId == null || selectElement.equals("")) { return; } // 一个CURD标签对应一个MappedStatement对象 // 一个MappedStatement对象由一个statementId来标识，所以保证唯一性 // statementId = namespace + "." + CRUD标签的id属性 statementId = namespace + "." + statementId; String parameterType = selectElement.attributeValue("parameterType"); Class<?> parameterClass = resolveType(parameterType); String resultType = selectElement.attributeValue("resultType"); Class<?> resultClass = resolveType(resultType); String statementType = selectElement.attributeValue("statementType"); statementType = statementType == null || statementType == "" ? "prepared" : statementType; // SqlSource的封装过程 SqlSource sqlSource = createSqlSource(selectElement); // TODO 建议使用构建者模式去优化 MappedStatement mappedStatement = new MappedStatement(statementId, parameterClass, resultClass, statementType, sqlSource); configuration.addMappedStatement(statementId, mappedStatement); } private SqlSource createSqlSource(Element selectElement) { return null; } private Class<?> resolveType(String parameterType) { try { Class<?> clazz = Class.forName(parameterType); return clazz; } catch (ClassNotFoundException e) { e.printStackTrace(); } return null; } /** * * @param environments * <environments> */ @SuppressWarnings("unchecked") private void parseEnvironments(Element environments) { String def = environments.attributeValue("default"); List<Element> envList = environments.elements(); for (Element element : envList) { String id = element.attributeValue("id"); if (id.equals(def)) { parseDataSource(element); } } } /** * * @param element * <environment> */ private void parseDataSource(Element element) { Element dataSourceElement = element.element("dataSource"); String type = dataSourceElement.attributeValue("type"); if (type.equals("DBCP")) { BasicDataSource dataSource = new BasicDataSource(); Properties properties = parseProperty(dataSourceElement); dataSource.setDriverClassName(properties.getProperty("driver")); dataSource.setUrl(properties.getProperty("url")); dataSource.setUsername(properties.getProperty("username")); dataSource.setPassword(properties.getProperty("password")); configuration.setDataSource(dataSource); } } @SuppressWarnings("unchecked") private Properties parseProperty(Element dataSourceElement) { Properties properties = new Properties(); List<Element> propElements = dataSourceElement.elements("property"); for (Element propElement : propElements) { String name = propElement.attributeValue("name"); String value = propElement.attributeValue("value"); properties.put(name, value); } return properties; } private Document createDocument(InputStream inputStream) { try { SAXReader saxReader = new SAXReader(); Document document = saxReader.read(inputStream); return document; } catch (Exception e) { } return null; } private InputStream getInputStream(String location) { InputStream inputStream = this.getClass().getClassLoader().getResourceAsStream(location); return inputStream; } @SuppressWarnings("unchecked") private <T> List<T> selectList(String statementId, Object paramObject) { Connection connection = null; PreparedStatement preparedStatement = null; ResultSet rs = null; // 要返回的结果集合 List<Object> results = new ArrayList<Object>(); try { // 获取数据源对象，通过数据源获取连接 connection = getConnection(configuration.getDataSource()); MappedStatement mappedStatement = configuration.getMappedStatementById(statementId); // 定义sql语句 ?表示占位符 SqlSource sqlSource = mappedStatement.getSqlSource(); // SqlSource的执行过程 BoundSql boundSql = sqlSource.getBoundSql(paramObject); String sql = boundSql.getSql(); // 获取预处理 statement preparedStatement = connection.prepareStatement(sql); // 设置参数 handleParameter(preparedStatement, mappedStatement, boundSql, paramObject); // 向数据库发出 sql 执行查询，查询出结果集 rs = preparedStatement.executeQuery(); // 获取要映射的结果类型 handleResultSet(rs, results, mappedStatement); } catch (Exception e) {