Mini MyBatis-Plus(下)

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最核心的内容前两篇已经讲完了，这一篇只有代码：

先看demo目录下的三个文件：

DemoApplication.java

package com.example.demo;import org.springframework.boot.SpringApplication;
import org.springframework.boot.autoconfigure.SpringBootApplication;@SpringBootApplication
public class DemoApplication {public static void main(String[] args) {SpringApplication.run(DemoApplication.class, args);}}

User.java

package com.example.demo;import com.example.demo.mybatisplus.annotations.TableName;
import lombok.AllArgsConstructor;
import lombok.Data;
import lombok.NoArgsConstructor;import java.util.Date;/*** @author mx*/
@Data
@TableName("t_user")
@AllArgsConstructor
@NoArgsConstructor
public class User {private Long id;private String name;private Integer age;private Date birthday;
}

UserMapper.java

package com.example.demo;import com.example.demo.mybatisplus.AbstractBaseMapper;/*** @author mx*/
public class UserMapper extends AbstractBaseMapper<User> {
}

mybatisplus下AbstractBaseMapper.java

package com.example.demo.mybatisplus;import com.example.demo.mybatisplus.annotations.TableName;
import com.example.demo.mybatisplus.core.JdbcTemplate;
import com.example.demo.mybatisplus.query.QueryWrapper;
import com.example.demo.mybatisplus.query.SqlParam;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;import java.lang.reflect.Field;
import java.lang.reflect.ParameterizedType;
import java.sql.SQLException;
import java.util.ArrayList;
import java.util.Collections;
import java.util.List;
import java.util.Map;/*** Mapper基类** @author mx*/
public abstract class AbstractBaseMapper<T> {private static Logger logger = LoggerFactory.getLogger(AbstractBaseMapper.class);private JdbcTemplate<T> jdbcTemplate = new JdbcTemplate<T>();private Class<T> beanClass;private final String TABLE_NAME;private static final String DEFAULT_LOGICAL_TYPE = " and ";public AbstractBaseMapper() {// DO对象的ClassbeanClass = (Class<T>) ((ParameterizedType) this.getClass().getGenericSuperclass()).getActualTypeArguments()[0];// DO对应的表名 TODO 非空判断及默认处理TABLE_NAME = beanClass.getAnnotation(TableName.class).value();}public T select(QueryWrapper<T> queryWrapper) {List<T> list = this.list(queryWrapper);if (!list.isEmpty()) {return list.get(0);}return null;}public List<T> list(QueryWrapper<T> queryWrapper) {StringBuilder sqlBuilder = new StringBuilder("SELECT * FROM ").append(TABLE_NAME).append(" WHERE ");List<Object> paramList = new ArrayList<>();Map<String, SqlParam> conditionMap = queryWrapper.build();conditionMap.forEach((operator, param) -> {sqlBuilder.append(param.getColumnName()).append(operator).append("?").append(DEFAULT_LOGICAL_TYPE);paramList.add(param.getValue());});// 删除最后一个 andString sql = sqlBuilder.replace(sqlBuilder.length() - DEFAULT_LOGICAL_TYPE.length(), sqlBuilder.length(), ";").toString();try {logger.info("sql: {}", sql);logger.info("params: {}", paramList);return jdbcTemplate.queryForList(sql, paramList, beanClass);} catch (Exception e) {e.printStackTrace();logger.error("query failed", e);}return Collections.emptyList();}public int insert(T bean) {// 得到DO对象的所有字段Field[] declaredFields = beanClass.getDeclaredFields();// 拼接sql语句，表名来自DO的TableName注解valueStringBuilder sqlBuilder = new StringBuilder().append("INSERT INTO ").append(TABLE_NAME).append(" VALUES(");for (int i = 0; i < declaredFields.length; i++) {sqlBuilder.append("?");if (i < declaredFields.length - 1) {sqlBuilder.append(",");}}sqlBuilder.append(")");// 收集sql参数ArrayList<Object> paramList = new ArrayList<>();try {for (Field declaredField : declaredFields) {declaredField.setAccessible(true);Object o = declaredField.get(bean);paramList.add(o);}} catch (IllegalAccessException e) {e.printStackTrace();}int affectedRows = 0;try {logger.info("sql: {}", sqlBuilder.toString());logger.info("params: {}", paramList);affectedRows = jdbcTemplate.update(sqlBuilder.toString(), paramList);logger.info("insert success, affectedRows: {}", affectedRows);return affectedRows;} catch (SQLException e) {e.printStackTrace();logger.error("insert failed", e);}return 0;}public int updateSelective(T bean, QueryWrapper<T> queryWrapper) {// 得到DO对象的所有字段Field[] declaredFields = beanClass.getDeclaredFields();// 拼接sql语句，表名来自DO的TableName注解valueStringBuilder sqlSetBuilder = new StringBuilder().append("UPDATE ").append(TABLE_NAME).append(" SET ");List<Object> paramList = new ArrayList<>();// 先拼接要SET的字段占位符 SET name=?, age=?try {for (int i = 0; i < declaredFields.length; i++) {Field declaredField = declaredFields[i];declaredField.setAccessible(true);Object fieldValue = declaredField.get(bean);if (fieldValue != null) {sqlSetBuilder.append(declaredField.getName()).append(" = ").append("?").append(", ");paramList.add(fieldValue);}}} catch (IllegalAccessException e) {e.printStackTrace();}// 删除最后一个 ,sqlSetBuilder = sqlSetBuilder.delete(sqlSetBuilder.length() - 2, sqlSetBuilder.length());// 再拼接WHERE条件占位符StringBuilder sqlWhereBuilder = new StringBuilder(" WHERE ");Map<String, SqlParam> conditionMap = queryWrapper.build();for (Map.Entry<String, SqlParam> stringSqlParamEntry : conditionMap.entrySet()) {String operator = stringSqlParamEntry.getKey();SqlParam param = stringSqlParamEntry.getValue();sqlWhereBuilder.append(param.getColumnName()).append(operator).append("?").append(DEFAULT_LOGICAL_TYPE);paramList.add(param.getValue());}// 删除最后一个 andsqlWhereBuilder = sqlWhereBuilder.replace(sqlWhereBuilder.length() - DEFAULT_LOGICAL_TYPE.length(), sqlWhereBuilder.length(), ";");String sql = sqlSetBuilder.append(sqlWhereBuilder).toString();int affectedRows = 0;try {logger.info("sql: {}", sqlSetBuilder.toString());logger.info("params: {}", paramList);affectedRows = jdbcTemplate.update(sql, paramList);logger.info("update success, affectedRows: {}", affectedRows);return affectedRows;} catch (SQLException e) {e.printStackTrace();logger.error("update failed", e);}return 0;}}

annotations下的TableName.java

package com.example.demo.mybatisplus.annotations;import java.lang.annotation.ElementType;
import java.lang.annotation.Retention;
import java.lang.annotation.RetentionPolicy;
import java.lang.annotation.Target;/*** @author mx*/
@Retention(RetentionPolicy.RUNTIME)
@Target(ElementType.TYPE)
public @interface TableName {String value();}

core下的

JdbcTemplate.java

package com.example.demo.mybatisplus.core;import java.lang.reflect.Field;
import java.sql.Connection;
import java.sql.DriverManager;
import java.sql.PreparedStatement;
import java.sql.ResultSet;
import java.sql.ResultSetMetaData;
import java.sql.SQLException;
import java.util.ArrayList;
import java.util.List;/*** JdbcTemplate，简化jdbc操作** @author mx*/
public class JdbcTemplate<T> {public List<T> queryForList(String sql, List<Object> params, RowMapper<T> rowMapper) throws SQLException {return query(sql, params, rowMapper);}public T queryForObject(String sql, List<Object> params, RowMapper<T> rowMapper) throws SQLException {List<T> result = query(sql, params, rowMapper);return result.isEmpty() ? null : result.get(0);}public List<T> queryForList(String sql, List<Object> params, Class<T> clazz) throws Exception {return query(sql, params, clazz);}public T queryForObject(String sql, List<Object> params, Class<T> clazz) throws Exception {List<T> result = query(sql, params, clazz);return result.isEmpty() ? null : result.get(0);}public int update(String sql, List<Object> params) throws SQLException {// 1.获取ConnectionConnection conn = getConnection();// 2.传入sql模板、sql参数，得到PreparedStatementPreparedStatement ps = getPreparedStatement(sql, params, conn);// 3.执行更新（增删改）int affectedRows = ps.executeUpdate();// 4.释放资源closeConnection(conn, ps, null);return affectedRows;}// ************************* private methods **************************private List<T> query(String sql, List<Object> params, RowMapper<T> rowMapper) throws SQLException {// 外部传入rowMapper（手写规则）return baseQuery(sql, params, rowMapper);}private List<T> query(String sql, List<Object> params, Class<T> clazz) throws Exception {// 自己创建rowMapper（反射）后传入BeanHandler<T> beanHandler = new BeanHandler<>(clazz);return baseQuery(sql, params, beanHandler);}/*** 基础查询方法，必须传入Bean的映射规则** @param sql* @param params* @param rowMapper* @return* @throws SQLException*/private List<T> baseQuery(String sql, List<Object> params, RowMapper<T> rowMapper) throws SQLException {// TODO 参数非空校验// 1.获取ConnectionConnection conn = getConnection();// 2.传入sql模板、sql参数，得到PreparedStatementPreparedStatement ps = getPreparedStatement(sql, params, conn);// 3.执行查询ResultSet rs = ps.executeQuery();// 4.处理结果List<T> result = new ArrayList<>();while (rs.next()) {T obj = rowMapper.mapRow(rs);result.add(obj);}// 5.释放资源closeConnection(conn, ps, rs);return result;}/*** 内部类，实现了RowMapper接口，底层使用反射** @param <R>*/private static class BeanHandler<R> implements RowMapper<R> {// clazz表示最终封装的bean类型private Class<R> clazz;public BeanHandler(Class<R> clazz) {this.clazz = clazz;}@Overridepublic R mapRow(ResultSet rs) {try {if (rs.next()) {// 1.获取表数据ResultSetMetaData metaData = rs.getMetaData();// 2.反射创建beanR bean = clazz.newInstance();// 3.利用反射，把表数据设置到bean中for (int i = 0; i < metaData.getColumnCount(); i++) {String name = metaData.getColumnName(i + 1);Object value = rs.getObject(name);Field field = clazz.getDeclaredField(name);field.setAccessible(true);field.set(bean, value);}// 4.返回beanreturn bean;} else {return null;}} catch (Exception e) {throw new RuntimeException(e);}}}private PreparedStatement getPreparedStatement(String sql, List<Object> params, Connection conn) throws SQLException {// 1.传入sql模板，得到PreparedStatementPreparedStatement ps = conn.prepareStatement(sql);// 2.为sql模板设置参数for (int i = 0; i < params.size(); i++) {ps.setObject(i + 1, params.get(i));}return ps;}private Connection getConnection() throws SQLException {// TODO 可以抽取配置到properties文件String url = "jdbc:mysql://localhost:3306/demo";String user = "root";String password = "123456";return DriverManager.getConnection(url, user, password);}private void closeConnection(Connection conn, PreparedStatement preparedStatement, ResultSet rs) throws SQLException {if (rs != null) {rs.close();}if (preparedStatement != null) {preparedStatement.close();}if (conn != null) {conn.close();}}}

RowMapper.java

package com.example.demo.mybatisplus.core;import java.sql.ResultSet;/*** 结果集映射器** @author mx*/
@FunctionalInterface
public interface RowMapper<T> {/*** 将结果集转为指定的Bean** @param resultSet* @return*/T mapRow(ResultSet resultSet);
}

query下的

QueryWrapper.java

package com.example.demo.mybatisplus.query;import com.example.demo.mybatisplus.utils.ConditionFunction;
import com.example.demo.mybatisplus.utils.Reflections;import java.util.HashMap;
import java.util.Map;/*** 模拟MyBatis-Plus的LambdaQueryWrapper（思路完全不同，仅仅是形似）** @author mx*/
public class QueryWrapper<T> {// conditionMap，收集查询条件// {//    " LIKE ": {//        "name": "bravo1988"//    },//    " = ": {//        "age": 18//    }// }private final Map<String, SqlParam> conditionMap = new HashMap<>();// 操作符类型，比如 name like 'bravo' 中的 LIKEprivate static final String OPERATOR_EQ = " = ";private static final String OPERATOR_GT = " > ";private static final String OPERATOR_LT = " < ";private static final String OPERATOR_LIKE = " LIKE ";public QueryWrapper<T> eq(ConditionFunction<T, ?> fn, Object value) {String columnName = Reflections.fnToColumnName(fn);conditionMap.put(OPERATOR_EQ, new SqlParam(columnName, value));return this;}public QueryWrapper<T> gt(ConditionFunction<T, ?> fn, Object value) {String columnName = Reflections.fnToColumnName(fn);conditionMap.put(OPERATOR_GT, new SqlParam(columnName, value));return this;}public QueryWrapper<T> lt(ConditionFunction<T, ?> fn, Object value) {String columnName = Reflections.fnToColumnName(fn);conditionMap.put(OPERATOR_LT, new SqlParam(columnName, value));return this;}public QueryWrapper<T> like(ConditionFunction<T, ?> fn, Object value) {String columnName = Reflections.fnToColumnName(fn);conditionMap.put(OPERATOR_LIKE, new SqlParam(columnName, "%" + value + "%"));return this;}public Map<String, SqlParam> build() {return conditionMap;}
}

SqlParam.java

package com.example.demo.mybatisplus.query;import lombok.AllArgsConstructor;
import lombok.Data;
import lombok.NoArgsConstructor;/*** @author mx*/
@Data
@NoArgsConstructor
@AllArgsConstructor
public class SqlParam {private String columnName;private Object value;
}

utils下的

ConditionFunction.java

package com.example.demo.mybatisplus.utils;import java.io.Serializable;
import java.util.function.Function;/*** 扩展java.util.function包下的Function接口：支持Serializable* 搭配Reflections工具类一起使用，用于获取Lambda表达式的方法名** @author mx*/
@FunctionalInterface
public interface ConditionFunction<T, R> extends Function<T, R>, Serializable {
}

Reflections.java

package com.example.demo.mybatisplus.utils;import java.beans.Introspector;
import java.lang.invoke.SerializedLambda;
import java.lang.reflect.Method;
import java.util.regex.Pattern;/*** 获取Lambda入参的方法名** @author mx*/
public class Reflections {private static final Pattern GET_PATTERN = Pattern.compile("^get[A-Z].*");private static final Pattern IS_PATTERN = Pattern.compile("^is[A-Z].*");/*** 注意: 非标准变量（非小驼峰）调用这个方法可能会有问题** @param fn* @param <T>* @return*/public static <T> String fnToColumnName(ConditionFunction<T, ?> fn) {try {Method method = fn.getClass().getDeclaredMethod("writeReplace");method.setAccessible(Boolean.TRUE);SerializedLambda serializedLambda = (SerializedLambda) method.invoke(fn);String getter = serializedLambda.getImplMethodName();// 对于非标准变量生成的Get方法这里可以直接抛出异常，或者打印异常日志if (GET_PATTERN.matcher(getter).matches()) {getter = getter.substring(3);} else if (IS_PATTERN.matcher(getter).matches()) {getter = getter.substring(2);}return Introspector.decapitalize(getter);} catch (ReflectiveOperationException e) {throw new RuntimeException(e);}}
}

其实第一篇的内容是最难的，不只是从0到1，而是从0到90，后面两篇其实只是90到100，在这基础稍微扩展了一下而已。

AbstractBaseMapper代码还有冗余，有兴趣的同学可以自行完善。但还是那句话，如果你的目的是为了锻炼封装能力，可以精益求精，但我们的AbstractBaseMapper注定不能用于生产，即使要优化，点到为止即可。

学习必须往深处挖，挖的越深，基础越扎实！

阶段1、深入多线程

阶段2、深入多线程设计模式

阶段3、深入juc源码解析

阶段4、深入jdk其余源码解析

阶段5、深入jvm源码解析