Mybatis注解手写源码篇

package com.example.demo.mybatis; import com.example.demo.User; import java.lang.reflect.*; import java.sql.*; import java.util.*; public class ProxyFactory { static String url="jdbc:mysql://localhost:3306/springcloud?characterEncoding=utf8"; static String username="root"; static String userpwd="123456"; private static Map<Class,TypeHandler> typeHandlerMap=new HashMap<>(); static { typeHandlerMap.put(String.class,new StringTypeHandler()); typeHandlerMap.put(Integer.class,new IntegerTypeHandler()); try { Class.forName("com.mysql.cj.jdbc.Driver"); } catch (ClassNotFoundException e) { e.printStackTrace(); } } public static <T> T getMapper(Class<T> mapper){ Object proxyInstance = Proxy.newProxyInstance(ClassLoader.getSystemClassLoader(), new Class[]{mapper}, new InvocationHandler() { @Override public Object invoke(Object proxy, Method method, Object[] args) throws Throwable { Connection connection = DriverManager.getConnection(url, username, userpwd); Select annotation = method.getAnnotation(Select.class); String value = annotation.value(); Map<String,Object> map=new HashMap<>(); //获得方法参数名称存放到map集合中，键为参数名称，值为参数数值 Parameter[] parameters = method.getParameters(); for (int i=0;i<parameters.length;i++) { String value1 = parameters[i].getAnnotation(Param.class).value(); map.put(value1,args[i]); map.put(parameters[i].getName(),args[i]); } //Mybatis占位符解析器 ParameterMappingTokenHandler parameterMappingTokenHandler=new ParameterMappingTokenHandler(); GenericTokenParser genericTokenParser=new GenericTokenParser("#{","}",parameterMappingTokenHandler); String parse = genericTokenParser.parse(value); //执行sql语句 PreparedStatement preparedStatement = connection.prepareStatement(parse); //获得sql语句{}内的参数名称 List<ParameterMapping> parameterMappingList = parameterMappingTokenHandler.getParameterMappingList(); for (int i=0;i<parameterMappingList.size();i++) { String property = parameterMappingList.get(i).getProperty(); Object o = map.get(property); Class<?> type = o.getClass(); //根据参数的不同类型执行不同preparedStatement的set方法 typeHandlerMap.get(type).setParameter(preparedStatement,i+1,o); } ResultSet resultSet = preparedStatement.executeQuery(); //获得方法的返回类型，根据是否是泛型进行判断，获得实体类的Class对象 Class resultType=null; Type genericReturnType = method.getGenericReturnType(); if(genericReturnType instanceof Class){ resultType=(Class)genericReturnType; } else if(genericReturnType instanceof ParameterizedType){ Type[] actualTypeArguments = ((ParameterizedType) genericReturnType).getActualTypeArguments(); resultType=(Class) actualTypeArguments[0]; } //获取数据库字段 ResultSetMetaData metaData = resultSet.getMetaData(); List<String> list=new ArrayList<>(); for(int i=0;i<metaData.getColumnCount();i++){ list.add(metaData.getColumnName(i+1)); } //将实体类的所有的set方法放到map集合中，键为属性名，值为对应的set方法 Map<String,Method> methodMap=new HashMap<>(); for (Method declaredMethod : resultType.getDeclaredMethods()) { if(declaredMethod.getName().startsWith("set")){ String substring = declaredMethod.getName().substring(3); substring=substring.substring(0,1).toLowerCase(Locale.ROOT)+substring.substring(1); methodMap.put(substring,declaredMethod); } } List<Object> resultlist=new ArrayList<>(); Object result=null; while (resultSet.next()){ Object instance = resultType.newInstance();//实体类必须有无参构造对象 for(int i=0;i<list.size();i++){ String column = list.get(i);//数据库字段 Method method1 = methodMap.get(column);//获得对应的set方法 Class clazz = method1.getParameterTypes()[0];//获得set方法参数 TypeHandler typeHandler = typeHandlerMap.get(clazz); method1.invoke(instance,typeHandler.getResult(resultSet,column)); } resultlist.add(instance); } if(method.getReturnType().equals(List.class)){ result=resultlist; }else { result=resultlist.get(0); } connection.close(); return result; } }); return (T) proxyInstance; }; }