学习文档 ----jdbc的中文文档 更多的是使用
http://www.mybatis.cn/archives/789.html
下面是mybatis的入门demo
<dependency> <groupId>org.mybatis</groupId> <artifactId>mybatis</artifactId> <version>x.x.x</version> </dependency> String resource = "org/mybatis/example/mybatis-config.xml"; InputStream inputStream = Resources.getResourceAsStream(resource); SqlSessionFactory sqlSessionFactory = new SqlSessionFactoryBuilder().build(inputStream); <?xml version="1.0" encoding="UTF-8" ?> <!DOCTYPE configuration PUBLIC "-//mybatis.org//DTD Config 3.0//EN" "http://mybatis.org/dtd/mybatis-3-config.dtd"> <configuration> <environments default="development"> <environment id="development"> <transactionManager type="JDBC"/> <dataSource type="POOLED"> <property name="driver" value="${driver}"/> <property name="url" value="${url}"/> <property name="username" value="${username}"/> <property name="password" value="${password}"/> </dataSource> </environment> </environments> <mappers> <mapper resource="org/mybatis/example/BlogMapper.xml"/> </mappers> </configuration> try (SqlSession session = sqlSessionFactory.openSession()) { BlogMapper mapper = session.getMapper(BlogMapper.class); Blog blog = mapper.selectBlog(101); }大家应该都能看懂 主要就是 SqlSessionFactory SqlSession Mapper的使用 实体类这里就不贴了 大家都会写
下面会一步步介绍 这几个底层说明
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JDBC为程序员提供了一套标准统一的API去访问不同的数据库。
JDBC访问数据库流程： （1）注册驱动 （2）建立连接 （3）创建数据库操作对象用于执行SQL的语句 （4）执行语句 （5）处理执行结果 （6）释放db资源
代码如下：
import java.sql.*; public class JDBConnection { public static String url_encrypt="jdbc:mysql://127.0.0.1:3306/student?useSSL=false"; public static String user="root"; public static String password="longdaye"; public static void main(String[] args) throws Exception { Class.forName("com.mysql.jdbc.Driver"); //建立数据库对象 Connection conn = DriverManager.getConnection(url_encrypt,user,password); //建立操作对象 Statement stmt= conn.createStatement(); //结果集 ResultSet rs = stmt.executeQuery("select * from information"); //依次输出结果集内容 while(rs.next()){ System.out.println( rs.getInt(1) + "\t" +rs.getString(2)+"\t" +rs.getString(3)+"\t" +rs.getInt(4)+"\t" +rs.getString(5)+"\t"); } //依次关闭结果集，操作对象，数据库对象 if(rs!=null){ rs.close(); } if(stmt!=null){ stmt.close(); } if(conn!=null){ conn.close(); } } }mybatis 底层使用的是PrepareStatement实现 。
PrepareStatement使用更方便一点，性能更好，且能避免sql注入，有了mybatis之后 我们不会去写这些代码。
PrepareStatement先写sql 再对sql中的参数？赋值 where pwd=‘1 or 1=1’
Statement 出来的是 where pwd='1‘ or 1=1 这样密码就无效了 所有的都会查出来
不是重点 jdbc都学过。
new SqlSessionFactoryBuilder().build(inputStream);
解析xml 文件 生成Configuration对象
源码如下：
//解析生成Configuration 对象 public Configuration parse() { if (parsed) { throw new BuilderException("Each XMLConfigBuilder can only be used once."); } parsed = true; parseConfiguration(parser.evalNode("/configuration")); return configuration; } //对应解析生成的不同节点 private void parseConfiguration(XNode root) { try { //issue #117 read properties first propertiesElement(root.evalNode("properties")); Properties settings = settingsAsProperties(root.evalNode("settings")); loadCustomVfs(settings); typeAliasesElement(root.evalNode("typeAliases")); pluginElement(root.evalNode("plugins")); objectFactoryElement(root.evalNode("objectFactory")); objectWrapperFactoryElement(root.evalNode("objectWrapperFactory")); reflectorFactoryElement(root.evalNode("reflectorFactory")); settingsElement(settings); // read it after objectFactory and objectWrapperFactory issue #631 environmentsElement(root.evalNode("environments")); databaseIdProviderElement(root.evalNode("databaseIdProvider")); typeHandlerElement(root.evalNode("typeHandlers")); //映射器的代码解析 mapperElement(root.evalNode("mappers")); } catch (Exception e) { throw new BuilderException("Error parsing SQL Mapper Configuration. Cause: " + e, e); } } private void mapperElement(XNode parent) throws Exception { if (parent != null) { for (XNode child : parent.getChildren()) { //package方式 if ("package".equals(child.getName())) { String mapperPackage = child.getStringAttribute("name"); configuration.addMappers(mapperPackage); } else { String resource = child.getStringAttribute("resource"); String url = child.getStringAttribute("url"); String mapperClass = child.getStringAttribute("class"); //3个属性只能配一个 //resouce方式---mapper.xml 常见 if (resource != null && url == null && mapperClass == null) { ErrorContext.instance().resource(resource); InputStream inputStream = Resources.getResourceAsStream(resource); XMLMapperBuilder mapperParser = new XMLMapperBuilder(inputStream, configuration, resource, configuration.getSqlFragments()); mapperParser.parse(); } else if (resource == null && url != null && mapperClass == null) { //url 远程机器上的输入流 ErrorContext.instance().resource(url); InputStream inputStream = Resources.getUrlAsStream(url); XMLMapperBuilder mapperParser = new XMLMapperBuilder(inputStream, configuration, url, configuration.getSqlFragments()); mapperParser.parse(); } else if (resource == null && url == null && mapperClass != null) { //class 指定一个接口 Class<?> mapperInterface = Resources.classForName(mapperClass); configuration.addMapper(mapperInterface); } else { throw new BuilderException("A mapper element may only specify a url, resource or class, but not more than one."); } } } } }不管是使用注解 还是使用xml 配置mapper的方法 最终都会转换成MappedStatement对象 ，将MappedStatement对象的属性加到Configuration里面
使用的StrictHashMap 同样的key put 会报错
如果同时配置了注解和xml 会报错 因为生成的MappedStatement的id相同 put的时候会报错
//解析xml中的文件 private void configurationElement(XNode context) { try { String namespace = context.getStringAttribute("namespace"); if (namespace == null || namespace.equals("")) { throw new BuilderException("Mapper's namespace cannot be empty"); } builderAssistant.setCurrentNamespace(namespace); cacheRefElement(context.evalNode("cache-ref")); cacheElement(context.evalNode("cache")); parameterMapElement(context.evalNodes("/mapper/parameterMap")); //resultmap resultMapElements(context.evalNodes("/mapper/resultMap")); sqlElement(context.evalNodes("/mapper/sql")); //增删改查 buildStatementFromContext(context.evalNodes("select|insert|update|delete")); } catch (Exception e) { throw new BuilderException("Error parsing Mapper XML. The XML location is '" + resource + "'. Cause: " + e, e); } } //解析buildStatementFromContext里面的每一个sql 解析里面的属性值 转换成MappedStatement public void parseStatementNode() { String id = context.getStringAttribute("id"); String databaseId = context.getStringAttribute("databaseId"); if (!databaseIdMatchesCurrent(id, databaseId, this.requiredDatabaseId)) { return; } Integer fetchSize = context.getIntAttribute("fetchSize"); Integer timeout = context.getIntAttribute("timeout"); String parameterMap = context.getStringAttribute("parameterMap"); String parameterType = context.getStringAttribute("parameterType"); Class<?> parameterTypeClass = resolveClass(parameterType); String resultMap = context.getStringAttribute("resultMap"); String resultType = context.getStringAttribute("resultType"); String lang = context.getStringAttribute("lang"); //语言解析器 解析#id 可以自己指定 默认是有的 XMLLanguageDriver LanguageDriver langDriver = getLanguageDriver(lang); Class<?> resultTypeClass = resolveClass(resultType); String resultSetType = context.getStringAttribute("resultSetType"); StatementType statementType = StatementType.valueOf(context.getStringAttribute("statementType", StatementType.PREPARED.toString())); ResultSetType resultSetTypeEnum = resolveResultSetType(resultSetType); String nodeName = context.getNode().getNodeName(); SqlCommandType sqlCommandType = SqlCommandType.valueOf(nodeName.toUpperCase(Locale.ENGLISH)); boolean isSelect = sqlCommandType == SqlCommandType.SELECT; boolean flushCache = context.getBooleanAttribute("flushCache", !isSelect); boolean useCache = context.getBooleanAttribute("useCache", isSelect); boolean resultOrdered = context.getBooleanAttribute("resultOrdered", false); // Include Fragments before parsing XMLIncludeTransformer includeParser = new XMLIncludeTransformer(configuration, builderAssistant); includeParser.applyIncludes(context.getNode()); // Parse selectKey after includes and remove them. processSelectKeyNodes(id, parameterTypeClass, langDriver); // Parse the SQL (pre: <selectKey> and <include> were parsed and removed) //核心 是转换成SqlSource $---对应的是动态sql 如果没有$都是#就是静态sql SqlSource sqlSource = langDriver.createSqlSource(configuration, context, parameterTypeClass); String resultSets = context.getStringAttribute("resultSets"); String keyProperty = context.getStringAttribute("keyProperty"); String keyColumn = context.getStringAttribute("keyColumn"); KeyGenerator keyGenerator; String keyStatementId = id + SelectKeyGenerator.SELECT_KEY_SUFFIX; keyStatementId = builderAssistant.applyCurrentNamespace(keyStatementId, true); if (configuration.hasKeyGenerator(keyStatementId)) { keyGenerator = configuration.getKeyGenerator(keyStatementId); } else { keyGenerator = context.getBooleanAttribute("useGeneratedKeys", configuration.isUseGeneratedKeys() && SqlCommandType.INSERT.equals(sqlCommandType)) ? Jdbc3KeyGenerator.INSTANCE : NoKeyGenerator.INSTANCE; } //增加MappedStatement builderAssistant.addMappedStatement(id, sqlSource, statementType, sqlCommandType, fetchSize, timeout, parameterMap, parameterTypeClass, resultMap, resultTypeClass, resultSetTypeEnum, flushCache, useCache, resultOrdered, keyGenerator, keyProperty, keyColumn, databaseId, langDriver, resultSets); }语言解析器 会将sql 转换成SqlSource 可以自己调试一下
select * from user where id = #{id}
语言解析器会解析成 select * from user where id = ？ -------------对应的就是jdbc的语法
执行sql的时候才对 ? 赋值
解析配置文件的时候sql 是什么样子 就是什么样子 执行的时候才会做
select * from user where id = ${id}
− − − 对 应 的 是 动 态 s q l 如 果 没 有 ---对应的是动态sql 如果没有 −−−对应的是动态sql如果没有都是#就是静态sql
动态sql 可能会出现sql注入 尽可能用#
动态sql 使用是在 select的值用
select ${id} from user;
这里不能用# 用#传进去的就是一个字符串 传的什么查的就是什么
session.getMapper(BlogMapper.class)
getMapper是利用动态代理获取 一个代理对象
public <T> T getMapper(Class<T> type, SqlSession sqlSession) { //利用代理工厂 final MapperProxyFactory<T> mapperProxyFactory = (MapperProxyFactory<T>) knownMappers.get(type); if (mapperProxyFactory == null) { throw new BindingException("Type " + type + " is not known to the MapperRegistry."); } try { //创建一个实例对象 调用的jdk的动态代理 return mapperProxyFactory.newInstance(sqlSession); } catch (Exception e) { throw new BindingException("Error getting mapper instance. Cause: " + e, e); } } protected T newInstance(MapperProxy<T> mapperProxy) { //jdk的动态代理 return (T) Proxy.newProxyInstance(mapperInterface.getClassLoader(), new Class[] { mapperInterface }, mapperProxy); } public T newInstance(SqlSession sqlSession) { final MapperProxy<T> mapperProxy = new MapperProxy<T>(sqlSession, mapperInterface, methodCache); return newInstance(mapperProxy); }调用方法的时候会进入到invoke
// MapperProxy @Override public Object invoke(Object proxy, Method method, Object[] args) throws Throwable { try { if (Object.class.equals(method.getDeclaringClass())) { return method.invoke(this, args); } else if (isDefaultMethod(method)) { return invokeDefaultMethod(proxy, method, args); } } catch (Throwable t) { throw ExceptionUtil.unwrapThrowable(t); } final MapperMethod mapperMethod = cachedMapperMethod(method); return mapperMethod.execute(sqlSession, args); } //方法的执行 MapperMethod public Object execute(SqlSession sqlSession, Object[] args) { Object result; switch (command.getType()) { case INSERT: { Object param = method.convertArgsToSqlCommandParam(args); result = rowCountResult(sqlSession.insert(command.getName(), param)); break; } case UPDATE: { Object param = method.convertArgsToSqlCommandParam(args); result = rowCountResult(sqlSession.update(command.getName(), param)); break; } case DELETE: { Object param = method.convertArgsToSqlCommandParam(args); result = rowCountResult(sqlSession.delete(command.getName(), param)); break; } case SELECT: if (method.returnsVoid() && method.hasResultHandler()) { executeWithResultHandler(sqlSession, args); result = null; } else if (method.returnsMany()) { result = executeForMany(sqlSession, args); } else if (method.returnsMap()) { result = executeForMap(sqlSession, args); } else if (method.returnsCursor()) { result = executeForCursor(sqlSession, args); } else { //转换函数参数到sql中的参数 @param注解 看参数使用的param1 param2 还是arg0 arg1 如果都没有会报错 或者用map 做函数的入参 Object param = method.convertArgsToSqlCommandParam(args); result = sqlSession.selectOne(command.getName(), param); } break; case FLUSH: result = sqlSession.flushStatements(); break; default: throw new BindingException("Unknown execution method for: " + command.getName()); } if (result == null && method.getReturnType().isPrimitive() && !method.returnsVoid()) { throw new BindingException("Mapper method '" + command.getName() + " attempted to return null from a method with a primitive return type (" + method.getReturnType() + ")."); } return result; } @Override public <E> List<E> selectList(String statement, Object parameter, RowBounds rowBounds) { try { MappedStatement ms = configuration.getMappedStatement(statement); //executor 执行最终的sql return executor.query(ms, wrapCollection(parameter), rowBounds, Executor.NO_RESULT_HANDLER); } catch (Exception e) { throw ExceptionFactory.wrapException("Error querying database. Cause: " + e, e); } finally { ErrorContext.instance().reset(); } } Object parameter, RowBounds rowBounds) { try { MappedStatement ms = configuration.getMappedStatement(statement); //executor 执行最终的sql return executor.query(ms, wrapCollection(parameter), rowBounds, Executor.NO_RESULT_HANDLER); } catch (Exception e) { throw ExceptionFactory.wrapException("Error querying database. Cause: " + e, e); } finally { ErrorContext.instance().reset(); } }