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本文主要研究一下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 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用于构造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来专门用于创建和往configuration添加MappedStatement
Configuration
org/apache/ibatis/session/Configuration.java
public class Configuration {
protected Environment environment;
protected final Map mappedStatements = new StrictMap(
"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 extends ConcurrentHashMap {
private static final long serialVersionUID = -4950446264854982944L;
private final String name;
private BiFunction 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方法，根据入参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 parameterMappings;
private final Object parameterObject;
private final Map additionalParameters;
private final MetaObject metaParameters;
//......
} BoundSql则代表了处理动态内容之后的SQL，该SQL可能还包含占位符
MappedStatement.getBoundSql
public BoundSql getBoundSql(Object parameterObject) {
BoundSql boundSql = sqlSource.getBoundSql(parameterObject);
List 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方法，在从sqlSource获取到的boundSql的parameterMappings为空时，会根据自己的ParameterMap的getParameterMappings来重新构建boundSql
DefaultSqlSession
org/apache/ibatis/session/defaults/DefaultSqlSession.java
private List 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方法则是根据statement从configuration获取到MappedStatement然后传递给executor
BaseExecutor
org/apache/ibatis/executor/BaseExecutor.java
public List 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，然后一路传递下去
小结
mybatis的MappedStatement是根据statementId从configuration获取的，这个是在启动的时候扫描注册上去的，因此如果通过反射改了MappedStatement会造成全局的影响，也可能有并发修改的问题；而BoundSql则是每次根据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，因而如果要在拦截器进行sql改动，改动BoundSql即可。