在上一章內(nèi)容中，我們介紹了ResultSetHandler的相關(guān)知識(shí)，但是又欠下了關(guān)于ResultSetWrapper封裝數(shù)據(jù)庫結(jié)果的類，我們先來整理下我們的技術(shù)債：
parameterHandler
ResultSetWrapper
下面就來進(jìn)入我們今天的正題。
1.ResultSetWrapper解析
我們先來看這個(gè)類的屬性和構(gòu)造方法：
public class ResultSetWrapper {
/**
* ResultSet 對(duì)象
*/
private final ResultSet resultSet;
private final TypeHandlerRegistry typeHandlerRegistry;
/**
* 字段的名字的數(shù)組
*/
private final List<String> columnNames = new ArrayList<>();
/**
* 字段的 Java Type 的數(shù)組
*/
private final List<String> classNames = new ArrayList<>();
/**
* 字段的 JdbcType 的數(shù)組
*/
private final List<JdbcType> jdbcTypes = new ArrayList<>();
private final Map<String, Map<Class<?>, TypeHandler<?>>> typeHandlerMap = new HashMap<>();
private final Map<String, List<String>> mappedColumnNamesMap = new HashMap<>();
private final Map<String, List<String>> unMappedColumnNamesMap = new HashMap<>();
public ResultSetWrapper(ResultSet rs, Configuration configuration) throws SQLException {
super();
this.typeHandlerRegistry = configuration.getTypeHandlerRegistry();
this.resultSet = rs;
// 遍歷 ResultSetMetaData 的字段們，解析出 columnNames、jdbcTypes、classNames 屬性
final ResultSetMetaData metaData = rs.getMetaData();
final int columnCount = metaData.getColumnCount();
for (int i = 1; i <= columnCount; i++) {
columnNames.add(configuration.isUseColumnLabel() ? metaData.getColumnLabel(i) : metaData.getColumnName(i));
jdbcTypes.add(JdbcType.forCode(metaData.getColumnType(i)));
classNames.add(metaData.getColumnClassName(i));
}
}
}
這里就是通過ResultSet拿到數(shù)據(jù)庫的列信息，然后進(jìn)行分類。
我們?cè)賮砜匆粋€(gè)這類的方法getTypeHandler：
public TypeHandler<?> getTypeHandler(Class<?> propertyType, String columnName) {
TypeHandler<?> handler = null;
Map<Class<?>, TypeHandler<?>> columnHandlers = typeHandlerMap.get(columnName);
if (columnHandlers == null) {
columnHandlers = new HashMap<>();
typeHandlerMap.put(columnName, columnHandlers);
} else {
handler = columnHandlers.get(propertyType);
}
if (handler == null) {
JdbcType jdbcType = getJdbcType(columnName);
handler = typeHandlerRegistry.getTypeHandler(propertyType, jdbcType);
// Replicate logic of UnknownTypeHandler#resolveTypeHandler
// See issue #59 comment 10
if (handler == null || handler instanceof UnknownTypeHandler) {
final int index = columnNames.indexOf(columnName);
final Class<?> javaType = resolveClass(classNames.get(index));
if (javaType != null && jdbcType != null) {
handler = typeHandlerRegistry.getTypeHandler(javaType, jdbcType);
} else if (javaType != null) {
handler = typeHandlerRegistry.getTypeHandler(javaType);
} else if (jdbcType != null) {
handler = typeHandlerRegistry.getTypeHandler(jdbcType);
}
}
if (handler == null || handler instanceof UnknownTypeHandler) {
handler = new ObjectTypeHandler();
}
columnHandlers.put(propertyType, handler);
}
return handler;
}
整體的邏輯就是把columnName的類型解析出來并緩存，如果沒有的定義的話，使用jdbc對(duì)應(yīng)的類型。
我們?cè)賮砜聪乱粋€(gè)類方法loadMappedAndUnmappedColumnNames：
private void loadMappedAndUnmappedColumnNames(ResultMap resultMap, String columnPrefix) throws SQLException {
List<String> mappedColumnNames = new ArrayList<>();
List<String> unmappedColumnNames = new ArrayList<>();
final String upperColumnPrefix = columnPrefix == null ? null : columnPrefix.toUpperCase(Locale.ENGLISH);
// 拼接前綴 prefix
final Set<String> mappedColumns = prependPrefixes(resultMap.getMappedColumns(), upperColumnPrefix);
for (String columnName : columnNames) {
final String upperColumnName = columnName.toUpperCase(Locale.ENGLISH);
if (mappedColumns.contains(upperColumnName)) {
mappedColumnNames.add(upperColumnName);
} else {
unmappedColumnNames.add(columnName);
}
}
mappedColumnNamesMap.put(getMapKey(resultMap, columnPrefix), mappedColumnNames);
unMappedColumnNamesMap.put(getMapKey(resultMap, columnPrefix), unmappedColumnNames);
}
這個(gè)方法比較眼熟，在我們上章映射數(shù)據(jù)結(jié)果時(shí)，如果沒有開啟自動(dòng)映射，則就是調(diào)用是對(duì)應(yīng) mappedColumn不然就是unMappedColumn。
這里的getMapKey和prependPrefixes方法也比較簡(jiǎn)單：
private String getMapKey(ResultMap resultMap, String columnPrefix) {
return resultMap.getId() + ":" + columnPrefix;
}
private Set<String> prependPrefixes(Set<String> columnNames, String prefix) {
if (columnNames == null || columnNames.isEmpty() || prefix == null || prefix.length() == 0) {
return columnNames;
}
final Set<String> prefixed = new HashSet<>();
for (String columnName : columnNames) {
prefixed.add(prefix + columnName);
}
return prefixed;
}
我們?cè)賮砜磳?duì)應(yīng)的自動(dòng)映射那個(gè)的方法：
public List<String> getMappedColumnNames(ResultMap resultMap, String columnPrefix) throws SQLException {
List<String> mappedColumnNames = mappedColumnNamesMap.get(getMapKey(resultMap, columnPrefix));
if (mappedColumnNames == null) {
loadMappedAndUnmappedColumnNames(resultMap, columnPrefix);
mappedColumnNames = mappedColumnNamesMap.get(getMapKey(resultMap, columnPrefix));
}
return mappedColumnNames;
}
public List<String> getUnmappedColumnNames(ResultMap resultMap, String columnPrefix) throws SQLException {
List<String> unMappedColumnNames = unMappedColumnNamesMap.get(getMapKey(resultMap, columnPrefix));
if (unMappedColumnNames == null) {
loadMappedAndUnmappedColumnNames(resultMap, columnPrefix);
unMappedColumnNames = unMappedColumnNamesMap.get(getMapKey(resultMap, columnPrefix));
}
return unMappedColumnNames;
}
這里的邏輯也比較簡(jiǎn)單，大家自行閱讀即可。
接下來我們來分析parameterHandler的源碼。
2. ParameterHandler解析
看這個(gè)類的名字，顧名思義就和參數(shù)的解析有關(guān)，我們來看下這個(gè)接口的源碼：
public interface ParameterHandler {
Object getParameterObject();
void setParameters(PreparedStatement ps)
throws SQLException;
}
也比較簡(jiǎn)單，而且這個(gè)接口也只有一個(gè)實(shí)現(xiàn)類DefaultParameterHandler，這個(gè)類也不復(fù)雜，我們就整體來看下：
public class DefaultParameterHandler implements ParameterHandler {
private final TypeHandlerRegistry typeHandlerRegistry;
private final MappedStatement mappedStatement;
private final Object parameterObject;
private final BoundSql boundSql;
private final Configuration configuration;
public DefaultParameterHandler(MappedStatement mappedStatement, Object parameterObject, BoundSql boundSql) {
this.mappedStatement = mappedStatement;
this.configuration = mappedStatement.getConfiguration();
this.typeHandlerRegistry = mappedStatement.getConfiguration().getTypeHandlerRegistry();
this.parameterObject = parameterObject;
this.boundSql = boundSql;
}
@Override
public Object getParameterObject() {
return parameterObject;
}
@Override
public void setParameters(PreparedStatement ps) {
ErrorContext.instance().activity("setting parameters").object(mappedStatement.getParameterMap().getId());
List<ParameterMapping> parameterMappings = boundSql.getParameterMappings();
if (parameterMappings != null) {
for (int i = 0; i < parameterMappings.size(); i++) {
ParameterMapping parameterMapping = parameterMappings.get(i);
if (parameterMapping.getMode() != ParameterMode.OUT) {
Object value;
String propertyName = parameterMapping.getProperty();
if (boundSql.hasAdditionalParameter(propertyName)) { // issue #448 ask first for additional params
value = boundSql.getAdditionalParameter(propertyName);
} else if (parameterObject == null) {
value = null;
} else if (typeHandlerRegistry.hasTypeHandler(parameterObject.getClass())) {
value = parameterObject;
} else {
MetaObject metaObject = configuration.newMetaObject(parameterObject);
value = metaObject.getValue(propertyName);
}
TypeHandler typeHandler = parameterMapping.getTypeHandler();
JdbcType jdbcType = parameterMapping.getJdbcType();
if (value == null && jdbcType == null) {
jdbcType = configuration.getJdbcTypeForNull();
}
try {
typeHandler.setParameter(ps, i + 1, value, jdbcType);
} catch (TypeException | SQLException e) {
throw new TypeException("Could not set parameters for mapping: " + parameterMapping + ". Cause: " + e, e);
}
}
}
}
}
}
這里看大致的意思就是PreparedStatement設(shè)置預(yù)編譯的變量。
3. 今日總結(jié)
今天主要還是把欠了的技術(shù)債都還了。我們也總結(jié)下：
- ResultSetWrapper是對(duì)數(shù)據(jù)返回的結(jié)果集進(jìn)行信息整理，以便使用
- parameterHandler主要是對(duì)PreparedStatement的參數(shù)注入。
