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本文次要钻研一下 mybatis MappedStatement
MappedStatement
org/apache/ibatis/mapping/MappedStatement.java
public final class MappedStatement {
private String resource;
private Configuration configuration;
private String id;
private Integer fetchSize;
private Integer timeout;
private StatementType statementType;
private ResultSetType resultSetType;
private SqlSource sqlSource;
private Cache cache;
private ParameterMap parameterMap;
private List<ResultMap> resultMaps;
private boolean flushCacheRequired;
private boolean useCache;
private boolean resultOrdered;
private SqlCommandType sqlCommandType;
private KeyGenerator keyGenerator;
private String[] keyProperties;
private String[] keyColumns;
private boolean hasNestedResultMaps;
private String databaseId;
private Log statementLog;
private LanguageDriver lang;
private String[] resultSets;
private boolean dirtySelect;
//......
}
MappedStatement 定义了 SqlSource
MappedStatement.Builder
public static class Builder {private final MappedStatement mappedStatement = new MappedStatement();
public Builder(Configuration configuration, String id, SqlSource sqlSource, SqlCommandType sqlCommandType) {
mappedStatement.configuration = configuration;
mappedStatement.id = id;
mappedStatement.sqlSource = sqlSource;
mappedStatement.statementType = StatementType.PREPARED;
mappedStatement.resultSetType = ResultSetType.DEFAULT;
mappedStatement.parameterMap = new ParameterMap.Builder(configuration, "defaultParameterMap", null,
new ArrayList<>()).build();
mappedStatement.resultMaps = new ArrayList<>();
mappedStatement.sqlCommandType = sqlCommandType;
mappedStatement.keyGenerator = configuration.isUseGeneratedKeys() && SqlCommandType.INSERT.equals(sqlCommandType)
? Jdbc3KeyGenerator.INSTANCE : NoKeyGenerator.INSTANCE;
String logId = id;
if (configuration.getLogPrefix() != null) {logId = configuration.getLogPrefix() + id;
}
mappedStatement.statementLog = LogFactory.getLog(logId);
mappedStatement.lang = configuration.getDefaultScriptingLanguageInstance();}
//......
}
MappedStatement 定义了一个 Builder 用于结构 MappedStatement
MapperBuilderAssistant
org/apache/ibatis/builder/MapperBuilderAssistant.java
public class MapperBuilderAssistant extends BaseBuilder {
public MappedStatement addMappedStatement(String id, SqlSource sqlSource, StatementType statementType,
SqlCommandType sqlCommandType, Integer fetchSize, Integer timeout, String parameterMap, Class<?> parameterType,
String resultMap, Class<?> resultType, ResultSetType resultSetType, boolean flushCache, boolean useCache,
boolean resultOrdered, KeyGenerator keyGenerator, String keyProperty, String keyColumn, String databaseId,
LanguageDriver lang, String resultSets, boolean dirtySelect) {if (unresolvedCacheRef) {throw new IncompleteElementException("Cache-ref not yet resolved");
}
id = applyCurrentNamespace(id, false);
MappedStatement.Builder statementBuilder = new MappedStatement.Builder(configuration, id, sqlSource, sqlCommandType)
.resource(resource).fetchSize(fetchSize).timeout(timeout).statementType(statementType)
.keyGenerator(keyGenerator).keyProperty(keyProperty).keyColumn(keyColumn).databaseId(databaseId).lang(lang)
.resultOrdered(resultOrdered).resultSets(resultSets)
.resultMaps(getStatementResultMaps(resultMap, resultType, id)).resultSetType(resultSetType)
.flushCacheRequired(flushCache).useCache(useCache).cache(currentCache).dirtySelect(dirtySelect);
ParameterMap statementParameterMap = getStatementParameterMap(parameterMap, parameterType, id);
if (statementParameterMap != null) {statementBuilder.parameterMap(statementParameterMap);
}
MappedStatement statement = statementBuilder.build();
configuration.addMappedStatement(statement);
return statement;
}
//......
}
MapperBuilderAssistant 定义了 addMappedStatement 来专门用于创立和往 configuration 增加 MappedStatement
Configuration
org/apache/ibatis/session/Configuration.java
public class Configuration {
protected Environment environment;
protected final Map<String, MappedStatement> mappedStatements = new StrictMap<MappedStatement>("Mapped Statements collection")
.conflictMessageProducer((savedValue, targetValue) -> ". please check" + savedValue.getResource() + "and"
+ targetValue.getResource());
//......
public void addMappedStatement(MappedStatement ms) {mappedStatements.put(ms.getId(), ms);
}
//......
}
Configuration 则定义了以 statementId 为 key,value 为 MappedStatement 的 StrictMap
Configuration.StrictMap
protected static class StrictMap<V> extends ConcurrentHashMap<String, V> {
private static final long serialVersionUID = -4950446264854982944L;
private final String name;
private BiFunction<V, V, String> conflictMessageProducer;
public StrictMap(String name, int initialCapacity, float loadFactor) {super(initialCapacity, loadFactor);
this.name = name;
}
public StrictMap(String name, int initialCapacity) {super(initialCapacity);
this.name = name;
}
//......
}
StrictMap 继承了 ConcurrentHashMap
SqlSource
org/apache/ibatis/mapping/SqlSource.java
/**
* Represents the content of a mapped statement read from an XML file or an annotation. It creates the SQL that will be
* passed to the database out of the input parameter received from the user.
*
* @author Clinton Begin
*/
public interface SqlSource {BoundSql getBoundSql(Object parameterObject);
}
而 SqlSource 接口则定义了 getBoundSql 办法,依据入参 parameterObject 来获取 BoundSql
SqlSource 有 DynamicSqlSource、ProviderSqlSource、RawSqlSource、StaticSqlSource 这四种实现
BoundSql
org/apache/ibatis/mapping/BoundSql.java
public class BoundSql {
private final String sql;
private final List<ParameterMapping> parameterMappings;
private final Object parameterObject;
private final Map<String, Object> additionalParameters;
private final MetaObject metaParameters;
//......
}
BoundSql 则代表了解决动静内容之后的 SQL,该 SQL 可能还蕴含占位符
MappedStatement.getBoundSql
public BoundSql getBoundSql(Object parameterObject) {BoundSql boundSql = sqlSource.getBoundSql(parameterObject);
List<ParameterMapping> parameterMappings = boundSql.getParameterMappings();
if (parameterMappings == null || parameterMappings.isEmpty()) {boundSql = new BoundSql(configuration, boundSql.getSql(), parameterMap.getParameterMappings(), parameterObject);
}
// check for nested result maps in parameter mappings (issue #30)
for (ParameterMapping pm : boundSql.getParameterMappings()) {String rmId = pm.getResultMapId();
if (rmId != null) {ResultMap rm = configuration.getResultMap(rmId);
if (rm != null) {hasNestedResultMaps |= rm.hasNestedResultMaps();
}
}
}
return boundSql;
}
MappedStatement 的 getBoundSql 办法,在从 sqlSource 获取到的 boundSql 的 parameterMappings 为空时,会依据本人的 ParameterMap 的 getParameterMappings 来从新构建 boundSql
DefaultSqlSession
org/apache/ibatis/session/defaults/DefaultSqlSession.java
private <E> List<E> selectList(String statement, Object parameter, RowBounds rowBounds, ResultHandler handler) {
try {MappedStatement ms = configuration.getMappedStatement(statement);
return executor.query(ms, wrapCollection(parameter), rowBounds, handler);
} catch (Exception e) {throw ExceptionFactory.wrapException("Error querying database. Cause:" + e, e);
} finally {ErrorContext.instance().reset();}
}
DefaultSqlSession 的 selectList 办法则是依据 statement 从 configuration 获取到 MappedStatement 而后传递给 executor
BaseExecutor
org/apache/ibatis/executor/BaseExecutor.java
public <E> List<E> query(MappedStatement ms, Object parameter, RowBounds rowBounds, ResultHandler resultHandler) throws SQLException {BoundSql boundSql = ms.getBoundSql(parameter);
CacheKey key = createCacheKey(ms, parameter, rowBounds, boundSql);
return query(ms, parameter, rowBounds, resultHandler, key, boundSql);
}
BaseExecutor 的 query 从 MappedStatement 获取到了 BoundSql,而后一路传递上来
小结
mybatis 的 MappedStatement 是依据 statementId 从 configuration 获取的,这个是在启动的时候扫描注册下来的,因而如果通过反射改了 MappedStatement 会造成全局的影响,也可能有并发批改的问题;而 BoundSql 则是每次依据 parameter 从 MappedStatement 获取的,而 MappedStatement 则是从 sqlSource 获取到的 BoundSql,因为每次入参都不同,所以这个 BoundSql 是每次执行都会 new 的,因此如果要在拦截器进行 sql 改变,改变 BoundSql 即可。