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本文主要研究一下mybatis MappedStatement
MappedStatement
org/apache/ibatis/mapping/MappedStatement.java
代码语言：javascript复制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
代码语言：javascript复制 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
代码语言：javascript复制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
代码语言：javascript复制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
代码语言：javascript复制 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
代码语言：javascript复制/**
* 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
代码语言：javascript复制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则代表了处理动态内容之后的SQL，该SQL可能还包含占位符
MappedStatement.getBoundSql
代码语言：javascript复制 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
代码语言：javascript复制 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
代码语言：javascript复制 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，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。
