程序浅谈 后端
2024-09-24
之前在Vertx项目中使用Tdengine，但Vertx没有Tdengine的异步JDBC驱动。所以只能使用Tdengine提供的同步JDBC驱动配合vertx.executeBlocking实现异步数据库查询。
原生的JDBC在SQL参数绑定和返回数据映射时很不方便。但当时第一印象是Mybatis和Spring结合太紧密了（实际是可以的哈），所以自己写了一个简单的SQL解析和返回数据映射的简单JDBC工具。但不能像Mybaits那样支持复杂的嵌套的类参数绑定和映射，但已经够用了。
首先要实现的功能：
实现效果：java
代码解读复制代码public class PropertyMapper extends BaseMapper {
public PropertyMapper(DataSource dataSource) {
super(dataSource);
}
public Integer add(PropertyEntity propertyEntity) {
// 实体类参数绑定到SQL
return update("INSERT INTO property VALUES (#{ts}, #{value});", propertyEntity);
}
public List<PropertyEntity> page(Long startTime, Long endTime, Long start, Long size) {
Map<String, Object> params = new MapBuilder().put("startTime", startTime)
.put("endTime", endTime)
.put("start", start)
.put("size", size)
.build();
// MAP参数绑定到SQL
return selectList("SELECT ts, value, property_code FROM property WHERE ts >= #{startTime} AND ts <= #{endTime} ORDER BY ts DESC LIMIT #{size} OFFSET #{start}", params, PropertyEntity.class);
}
public class PropertyEntity {
/**
* 时间戳, 精确到ms
*/
@TableField(typeHandler = OffsetDateTimeToLongHandler.class, value = "ts")
private Long ts;
/**
* 值, 不同产品属性定义的超级表值类型不同
*/
private Object value;
/**
* 属性编码
*/
private String propertyCode;
}
对比下原生实现，原生的很多重复代码，同时预编译SQL中参数占位符号都是?区分度差了，每次写的时候还要将参数和?的序列对应起来（JDBC中?index从1开始）可能导致绑定参数错误，java
代码解读复制代码PreparedStatementpsmt = null;
ResultSetrs = null;
try {
Connectionconn = null;
conn =JdbcUtils.getConnection();
Stringsql = "SELECT ts, value, property_code FROM property WHERE ts >= ? AND ts <= ? ORDER BY ts DESC LIMIT ? OFFSET ?";
psmt =conn.prepareStatement(sql);
//绑定参数到预编译SQL
psmt.setLong(1,startTime);
psmt.setLong(1,endTime);
psmt.setLong(1,start);
psmt.setLong(1,size);
rs =psmt.executeQuery();
List<PropertyEntity> result = new ArrayList<>();
while(rs.next()){
//解析返回值
Long ts = rs.getLong("ts");
Object value = rs.getObject("value");
String propertyCode = rs.getObject("property_code");
PropertyEntity property = new PropertyEntity();
property.setTs(ts);
property.setValue(value);
property.setPropertyCode(propertyCode);
result.add(property);
}
return result;
} catch(Exception e) {
throw new RuntimeException(e);
} finally{
JdbcUtils.closeResource(conn,psmt, rs);
}
实现SQL参数绑定，支持实体类和MAP绑定到SQLjava
代码解读复制代码INSERT INTO property VALUES (#{ts}, #{value});
SELECT ts, value, property_code FROM property WHERE ts >= #{startTime} AND ts <= #{endTime} ORDER BY ts DESC LIMIT #{size} OFFSET #{start}
代码解读复制代码/**
* obj根据属性名映射到sql 占位符 #{ts}
*/
public static SqlAndParamDTO objMapToSqlParam(String sql, Object po) {
return toSqlParam(sql, poToMap(po, false));
}
/**
* map参数更加key映射到sql
*/
public static SqlAndParamDTO toSqlParam(String sql, Map<String, Object> paramMap) {
if (paramMap == null || paramMap.isEmpty()) {
return SqlAndParamDTO.builder().paramList(Collections.emptyList()).sql(sql).build();
}
List<Object> params = new ArrayList<>();
String regex = "#\{\s*([^\{\}\s]*)\s*\}";
Pattern pattern = Pattern.compile(regex);
Matcher matcher = pattern.matcher(sql);
StringBuilder sb = new StringBuilder();
String placeholder = "?";
while (matcher.find()) {
//占位符
String poParamName = matcher.group(1);
Object paramValue = paramMap.get(poParamName);
matcher.appendReplacement(sb, placeholder);
params.add(paramValue);
}
matcher.appendTail(sb);
return SqlAndParamDTO.builder().paramList(params).sql(sql).build();
}
/**
* 将po转Map
* 属性名称--->属性值
*
* @param po 需要转换的对象
* @param underScore 是否取下划线即注解值
*/
public static Map<String, Object> poToMap(Object po, Boolean underScore) {
if (po == null) {
return Collections.emptyMap();
}
Map<String, Object> paramMap = new HashMap<>(16);
// getField只能够获取类的共有属性字段 也就是public修饰的
Field[] fields = FieldUtil.getAllFields(po.getClass());
for (Field field : fields) {
field.setAccessible(true);
TableField tableField = field.getDeclaredAnnotation(TableField.class);
String fieldName = underScore ? tableField.value() : field.getName();
try {
paramMap.put(fieldName, field.get(po));
} catch (IllegalAccessException e) {
throw new RuntimeException("参数绑定出错");
}
}
return paramMap;
}
public static PreparedStatement getPreparedStatement(Connection connection, String sql, List params) throws SQLException {
PreparedStatement preparedStatement = connection.prepareStatement(sql);
for (int i = 1; i <= params.size(); i++) {
//jdbc预编译参数从1起步
preparedStatement.setObject(i, params.get(i - 1));
}
return preparedStatement;
}
@Data
@Builder
public static class SqlAndParamDTO {
/**
* 生成的预编译sql
*/
public String sql;
/**
* 生成对应预编译参数位置的数组
*/
private List paramList;
}
这里没做集合类型支持，比如当参数类型为List时可以生成对应数量的?，golang中的gorm也是这样实现的。
核心BaseMapper
很神奇只需要写两个方法就可以解决所有SQL查询了
SQL只有两类更新SQL和查询SQL，分别对应JDBC的 preparedStatement.executeQuery()，reparedStatement.executeUpdate()。对应我们的也就两个函数：selectList和updatejava
代码解读复制代码public class BaseMapper {
private DataSource dataSource;
/**
* getOne之类查询
*
* @param sql sql
* @param valueMap 参数， 因为查询一般参数都是零散的没有提供Obj参数绑定方法要写页很简单
* @param rClass 返回值类型
*/
public <R> R selectOne(String sql, Map<String, Object> valueMap, Class<R> rClass) {
List<R> result = selectList(sql, valueMap, rClass);
if (result == null || result.isEmpty()) {
return null;
}
if (result.size() == 1) {
return result.get(0);
}
throw new RuntimeException("except one but more than one");
}
/**
* 查询list
*
* @param sql sql
* @param valueMap 参数
* @param rClass 返回值类型
*/
public <R> List<R> selectList(String sql, Map<String, Object> valueMap, Class<R> rClass) {
ParamUtil.SqlAndParamDTO sqlAndParamDTO = ParamUtil.toSqlParam(sql, valueMap);
Connection connection = null;
PreparedStatement preparedStatement = null;
ResultSet resultSet = null;
try {
connection = dataSource.getConnection();
preparedStatement = getPreparedStatement(connection, sqlAndParamDTO.getSql(), sqlAndParamDTO.getParamList());
resultSet = preparedStatement.executeQuery();
return ResultConvertUtil.listFromResultSet(resultSet, rClass);
} catch (Exception e) {
throw new RuntimeException(e);
} finally {
close(resultSet, preparedStatement, connection);
}
}
/**
* 更新sql: insert, delete, update
*
* @param sql sql
* @param paramObj Obj参数
* @return {@link Future}<{@link Integer}>
*/
public Integer update(String sql, Object paramObj) {
//将Object转换为Map
return update(sql, ParamUtil.poToMap(paramObj, false));
}
/**
* 更新sql: insert, delete, update
*
* @param sql sql
* @param paramMap map类型参数
* @return {@link Future}<{@link Integer}>
*/
public Integer update(String sql, Map<String, Object> paramMap) {
ParamUtil.SqlAndParamDTO sqlAndParamDTO = ParamUtil.toSqlParam(sql, paramMap);
Connection connection = null;
PreparedStatement preparedStatement = null;
try {
connection = dataSource.getConnection();
preparedStatement = getPreparedStatement(connection, sqlAndParamDTO.getSql(), sqlAndParamDTO.getParamList());
return preparedStatement.executeUpdate();
} catch (Exception e) {
throw new RuntimeException(e);
} finally {
//关闭资源让线程池回收
close(null, preparedStatement, connection);
}
}
}
实现返回值映射到实体类Tdengine返回的是ResultSet和其他JDBC驱动有些不同，Postgres返回的是RowSet rowSet但实现是一样的。主要步骤就是：
代码解读复制代码/**
* 从resultSet获取结果
* @param resultSet
* @param targetClass
* @return {@link List}<{@link R}>
* @throws SQLException
*/
public static <R> List<R> listFromResultSet(ResultSet resultSet, Class<R> targetClass) throws SQLException {
if (resultSet == null) {
return Collections.emptyList();
}
List<R> resultList = new ArrayList<>(20);
//如果是基本类型或者String直接取第一个返回
if (CommonUtil.isPrimitive(targetClass) || String.class == targetClass) {
while (resultSet.next()) {
if (String.class == targetClass) {
resultList.add((R) resultSet.getString(1));
} else {
resultList.add((R) resultSet.getObject(1));
}
}
return resultList;
}
//如果是对象映射结果返回
while (resultSet.next()) {
Map<String, Object> sqlRowToValueMap = new HashMap<>(8);
ResultSetMetaData rowMetaData = resultSet.getMetaData();
int columnCount = rowMetaData.getColumnCount();
for (int i = 1; i <= columnCount; i++) {
sqlRowToValueMap.put(rowMetaData.getColumnLabel(i), resultSet.getObject(i));
}
resultList.add(mapToObj(sqlRowToValueMap, targetClass));
}
return resultList;
}
/**
* map值映射Obj
*
* @param valueMap
* @param rClass
* @return {@link R}
*/
public static <R> R mapToObj(Map<String, Object> valueMap, Class<R> rClass) {
try {
//反射出对象
R r = rClass.getDeclaredConstructor().newInstance();
Field[] fields = FieldUtil.getAllFields(rClass);
for (Field field : fields) {
field.setAccessible(true);
TableField tableField = field.getDeclaredAnnotation(TableField.class);
TypeHandler<?> typeHandler = null;
if (tableField != null && tableField.typeHandler() != null) {
typeHandler = tableField.typeHandler().getDeclaredConstructor().newInstance();
}
//如果有注解用注解没有用字段名改为下划线，支持注解定义别名。同时避免数据库short和java int long转换异常提供了变量提升
String realFieldName = tableField == null ? poParamNameToDb(field.getName()) : tableField.value();
field.set(r, typeHandler == null || typeHandler instanceof UnknownTypeHandler ? varLift(valueMap.get(realFieldName), field.getType()) : typeHandler.getResult(valueMap.get(realFieldName)));
}
return r;
} catch (Exception e) {
throw new RuntimeException("sql result to Object error:", e);
}
}
/**
* 变量提升
*
* @param oldVar
* @param targetClass
* @return {@link Object}
*/
public static Object varLift(Object oldVar, Class<?> targetClass) {
if (oldVar == null) {
return null;
}
if (oldVar instanceof Integer && targetClass.equals(Long.class)) {
return ((Integer) oldVar).longValue();
}
if (oldVar instanceof Short && targetClass.equals(Long.class)) {
return ((Short) oldVar).longValue();
}
if (oldVar instanceof Short && targetClass.equals(Integer.class)) {
return ((Short) oldVar).intValue();
}
if (targetClass.equals(String.class) && oldVar instanceof byte[]) {
return new String((byte[]) oldVar, StandardCharsets.UTF_8);
}
return oldVar;
}
基本实现了Mybatis核心功能，其实不复杂，但够用了。但是Mybatis支持的太多啦，加上需要整合SpringBoot所以比较复杂。
