SqlSession 到我们想要的数据到底经过了什么？
比如查询吧：
1> 从Configuration中获取MappedStatement即你在xml写的一条sql含占位符
2> 执行去执行：涉及传参、jdbcType和javaType转化（typeHandler）、结果集封装，分页等
@Override
public void select(String statement, Object parameter, RowBounds rowBounds, ResultHandler handler) {
try {
MappedStatement ms = configuration.getMappedStatement(statement);
executor.query(ms, wrapCollection(parameter), rowBounds, handler);
} catch (Exception e) {
throw ExceptionFactory.wrapException("Error querying database. Cause: " + e, e);
} finally {
ErrorContext.instance().reset();
}
}
其实从上面还是看不到我在xml配置namespace和select标签id 是如何运行的啊？
1> 从MapperProxy代理类
MapperProxy-->MapperProxyFactory-->MapperRegistry-->Configuration-->SqlSession的getMapper
也就是说通过SqlSession.getMapper获取的就是MapperProxy这个代理类mapper
mapper执行任何方法都会调用invoke方法，关键就是invoke的mapperMethod.execute方法
2> 执行MapperMethod的execute方法就根据命令类型再进入SqlSession的相应方法
源码总有讲完了：映射器那块的源码涉及太多，不想深挖了
从SqlSession的四个对象：
1> Executor 执行器：他才是真正的老大，调度StatementHandler、ParameterHandler、ResultHandler等运行
2>StatementHandler:他是老大最得力大将，就是使用数据库的Statement(eg:PreparedStaement)进行操作
3> ParameterHandler:对SQL进行参数处理
4> ResultHandler:对SQL执行后的结果集/ResultSet进行数据封装
这个4个对象：就是说谁来执行，谁处理预编译，谁处理传参，谁处理结果集；想想我们的映射器
映射器：2个重要类
1> MappedStatement :xml中，一个sql对应一个MappedStatement对象
2> BoundSql:为sql传参
前奏：
public class RowBounds { //作用2个：分页和 list 查询时控制最多返回数
public static final int NO_ROW_OFFSET = 0;
public static final int NO_ROW_LIMIT = 2147483647;
public static final RowBounds DEFAULT = new RowBounds();
private int offset;
private int limit;
public RowBounds() { this.offset = 0; this.limit = 2147483647; }
public RowBounds(int offset, int limit) { this.offset = offset; this.limit = limit; }
public int getOffset() { return this.offset; }
public int getLimit() { return this.limit; }
}
public interface SqlSource { //从xml或注解获取MapperStatment的内容；并处理给SQL传参
BoundSql getBoundSql(Object parameterObject); //本质上干活的还是BoundSql
}
public class BoundSql {
private String sql; //就是我们写的sql语句可以含占位符，使用过ibatis的都很熟悉
private List<ParameterMapping> parameterMappings;
private Object parameterObject; //参数本身
private Map<String, Object> additionalParameters;
private MetaObject metaParameters;
public BoundSql(Configuration configuration, String sql, List<ParameterMapping> parameterMappings, Object parameterObject) {
this.sql = sql;
this.parameterMappings = parameterMappings;
this.parameterObject = parameterObject;
this.additionalParameters = new HashMap<String, Object>();
this.metaParameters = configuration.newMetaObject(additionalParameters);
}
public String getSql() {
return sql;
}
public List<ParameterMapping> getParameterMappings() {
return parameterMappings;
}
public Object getParameterObject() {
return parameterObject;
}
public boolean hasAdditionalParameter(String name) {
String paramName = new PropertyTokenizer(name).getName();
return additionalParameters.containsKey(paramName);
}
public void setAdditionalParameter(String name, Object value) {
metaParameters.setValue(name, value);
}
public Object getAdditionalParameter(String name) {
return metaParameters.getValue(name);
}
}
public class MapperMethod { //告诉xml映射文件和接口如何绑定和MappedStatement是什么（MapperBuilderAssistant）
private final SqlCommand command;
private final MethodSignature method;
public MapperMethod(Class<?> mapperInterface, Method method, Configuration config) {
this.command = new SqlCommand(config, mapperInterface, method);
this.method = new MethodSignature(config, mapperInterface, method);
}
public Object execute(SqlSession sqlSession, Object[] args) {
Object result;
switch (command.getType()) {
case INSERT: {
Object param = method.convertArgsToSqlCommandParam(args);
result = rowCountResult(sqlSession.insert(command.getName(), param));
break;
}
case UPDATE: {
Object param = method.convertArgsToSqlCommandParam(args);
result = rowCountResult(sqlSession.update(command.getName(), param));
break;
}
case DELETE: {
Object param = method.convertArgsToSqlCommandParam(args);
result = rowCountResult(sqlSession.delete(command.getName(), param));
break;
}
case SELECT:
if (method.returnsVoid() && method.hasResultHandler()) {
executeWithResultHandler(sqlSession, args);
result = null;
} else if (method.returnsMany()) {
result = executeForMany(sqlSession, args);
} else if (method.returnsMap()) {
result = executeForMap(sqlSession, args);
} else if (method.returnsCursor()) {
result = executeForCursor(sqlSession, args);
} else {
Object param = method.convertArgsToSqlCommandParam(args);
result = sqlSession.selectOne(command.getName(), param);
}
break;
case FLUSH:
result = sqlSession.flushStatements();
break;
default:
throw new BindingException("Unknown execution method for: " + command.getName());
}
if (result == null && method.getReturnType().isPrimitive() && !method.returnsVoid()) {
throw new BindingException("Mapper method '" + command.getName()
+ " attempted to return null from a method with a primitive return type (" + method.getReturnType() + ").");
}
return result;
}
private Object rowCountResult(int rowCount) {
final Object result;
if (method.returnsVoid()) {
result = null;
} else if (Integer.class.equals(method.getReturnType()) || Integer.TYPE.equals(method.getReturnType())) {
result = rowCount;
} else if (Long.class.equals(method.getReturnType()) || Long.TYPE.equals(method.getReturnType())) {
result = (long)rowCount;
} else if (Boolean.class.equals(method.getReturnType()) || Boolean.TYPE.equals(method.getReturnType())) {
result = rowCount > 0;
} else {
throw new BindingException("Mapper method '" + command.getName() + "' has an unsupported return type: " + method.getReturnType());
}
return result;
}
private void executeWithResultHandler(SqlSession sqlSession, Object[] args) {
MappedStatement ms = sqlSession.getConfiguration().getMappedStatement(command.getName());
if (void.class.equals(ms.getResultMaps().get(0).getType())) {
throw new BindingException("method " + command.getName()
+ " needs either a @ResultMap annotation, a @ResultType annotation,"
+ " or a resultType attribute in XML so a ResultHandler can be used as a parameter.");
}
Object param = method.convertArgsToSqlCommandParam(args);
if (method.hasRowBounds()) {
RowBounds rowBounds = method.extractRowBounds(args);
sqlSession.select(command.getName(), param, rowBounds, method.extractResultHandler(args));
} else {
sqlSession.select(command.getName(), param, method.extractResultHandler(args));
}
}
private <E> Object executeForMany(SqlSession sqlSession, Object[] args) {
List<E> result;
Object param = method.convertArgsToSqlCommandParam(args);
if (method.hasRowBounds()) {
RowBounds rowBounds = method.extractRowBounds(args);
result = sqlSession.<E>selectList(command.getName(), param, rowBounds);
} else {
result = sqlSession.<E>selectList(command.getName(), param);
}
// issue #510 Collections & arrays support
if (!method.getReturnType().isAssignableFrom(result.getClass())) {
if (method.getReturnType().isArray()) {
return convertToArray(result);
} else {
return convertToDeclaredCollection(sqlSession.getConfiguration(), result);
}
}
return result;
}
private <T> Cursor<T> executeForCursor(SqlSession sqlSession, Object[] args) {
Cursor<T> result;
Object param = method.convertArgsToSqlCommandParam(args);
if (method.hasRowBounds()) {
RowBounds rowBounds = method.extractRowBounds(args);
result = sqlSession.<T>selectCursor(command.getName(), param, rowBounds);
} else {
result = sqlSession.<T>selectCursor(command.getName(), param);
}
return result;
}
private <E> Object convertToDeclaredCollection(Configuration config, List<E> list) {
Object collection = config.getObjectFactory().create(method.getReturnType());
MetaObject metaObject = config.newMetaObject(collection);
metaObject.addAll(list);
return collection;
}
@SuppressWarnings("unchecked")
private <E> Object convertToArray(List<E> list) {
Class<?> arrayComponentType = method.getReturnType().getComponentType();
Object array = Array.newInstance(arrayComponentType, list.size());
if (arrayComponentType.isPrimitive()) {
for (int i = 0; i < list.size(); i++) {
Array.set(array, i, list.get(i));
}
return array;
} else {
return list.toArray((E[])array);
}
}
private <K, V> Map<K, V> executeForMap(SqlSession sqlSession, Object[] args) {
Map<K, V> result;
Object param = method.convertArgsToSqlCommandParam(args);
if (method.hasRowBounds()) {
RowBounds rowBounds = method.extractRowBounds(args);
result = sqlSession.<K, V>selectMap(command.getName(), param, method.getMapKey(), rowBounds);
} else {
result = sqlSession.<K, V>selectMap(command.getName(), param, method.getMapKey());
}
return result;
}
public static class ParamMap<V> extends HashMap<String, V> {
private static final long serialVersionUID = -2212268410512043556L;
@Override
public V get(Object key) {
if (!super.containsKey(key)) {
throw new BindingException("Parameter '" + key + "' not found. Available parameters are " + keySet());
}
return super.get(key);
}
}
public static class SqlCommand {
private final String name;
private final SqlCommandType type;
public SqlCommand(Configuration configuration, Class<?> mapperInterface, Method method) {
final String methodName = method.getName();
final Class<?> declaringClass = method.getDeclaringClass();
MappedStatement ms = resolveMappedStatement(mapperInterface, methodName, declaringClass,
configuration);
if (ms == null) {
if (method.getAnnotation(Flush.class) != null) {
name = null;
type = SqlCommandType.FLUSH;
} else {
throw new BindingException("Invalid bound statement (not found): "
+ mapperInterface.getName() + "." + methodName);
}
} else {
name = ms.getId();
type = ms.getSqlCommandType();
if (type == SqlCommandType.UNKNOWN) {
throw new BindingException("Unknown execution method for: " + name);
}
}
}
public String getName() {
return name;
}
public SqlCommandType getType() {
return type;
}
private MappedStatement resolveMappedStatement(Class<?> mapperInterface, String methodName,
Class<?> declaringClass, Configuration configuration) {
String statementId = mapperInterface.getName() + "." + methodName;
if (configuration.hasStatement(statementId)) {
return configuration.getMappedStatement(statementId);
} else if (mapperInterface.equals(declaringClass)) {
return null;
}
for (Class<?> superInterface : mapperInterface.getInterfaces()) {
if (declaringClass.isAssignableFrom(superInterface)) {
MappedStatement ms = resolveMappedStatement(superInterface, methodName,
declaringClass, configuration);
if (ms != null) {
return ms;
}
}
}
return null;
}
}
public static class MethodSignature {
private final boolean returnsMany;
private final boolean returnsMap;
private final boolean returnsVoid;
private final boolean returnsCursor;
private final Class<?> returnType;
private final String mapKey;
private final Integer resultHandlerIndex;
private final Integer rowBoundsIndex;
private final ParamNameResolver paramNameResolver;
public MethodSignature(Configuration configuration, Class<?> mapperInterface, Method method) {
Type resolvedReturnType = TypeParameterResolver.resolveReturnType(method, mapperInterface);
if (resolvedReturnType instanceof Class<?>) {
this.returnType = (Class<?>) resolvedReturnType;
} else if (resolvedReturnType instanceof ParameterizedType) {
this.returnType = (Class<?>) ((ParameterizedType) resolvedReturnType).getRawType();
} else {
this.returnType = method.getReturnType();
}
this.returnsVoid = void.class.equals(this.returnType);
this.returnsMany = (configuration.getObjectFactory().isCollection(this.returnType) || this.returnType.isArray());
this.returnsCursor = Cursor.class.equals(this.returnType);
this.mapKey = getMapKey(method);
this.returnsMap = (this.mapKey != null);
this.rowBoundsIndex = getUniqueParamIndex(method, RowBounds.class);
this.resultHandlerIndex = getUniqueParamIndex(method, ResultHandler.class);
this.paramNameResolver = new ParamNameResolver(configuration, method);
}
public Object convertArgsToSqlCommandParam(Object[] args) {
return paramNameResolver.getNamedParams(args);
}
public boolean hasRowBounds() {
return rowBoundsIndex != null;
}
public RowBounds extractRowBounds(Object[] args) {
return hasRowBounds() ? (RowBounds) args[rowBoundsIndex] : null;
}
public boolean hasResultHandler() {
return resultHandlerIndex != null;
}
public ResultHandler extractResultHandler(Object[] args) {
return hasResultHandler() ? (ResultHandler) args[resultHandlerIndex] : null;
}
public String getMapKey() {
return mapKey;
}
public Class<?> getReturnType() {
return returnType;
}
public boolean returnsMany() {
return returnsMany;
}
public boolean returnsMap() {
return returnsMap;
}
public boolean returnsVoid() {
return returnsVoid;
}
public boolean returnsCursor() {
return returnsCursor;
}
private Integer getUniqueParamIndex(Method method, Class<?> paramType) {
Integer index = null;
final Class<?>[] argTypes = method.getParameterTypes();
for (int i = 0; i < argTypes.length; i++) {
if (paramType.isAssignableFrom(argTypes[i])) {
if (index == null) {
index = i;
} else {
throw new BindingException(method.getName() + " cannot have multiple " + paramType.getSimpleName() + " parameters");
}
}
}
return index;
}
private String getMapKey(Method method) {
String mapKey = null;
if (Map.class.isAssignableFrom(method.getReturnType())) {
final MapKey mapKeyAnnotation = method.getAnnotation(MapKey.class);
if (mapKeyAnnotation != null) {
mapKey = mapKeyAnnotation.value();
}
}
return mapKey;
}
}
}