在上一篇文章我们已经得到了mapper的代理对象，接下来我们对demoMapper.getDemo(1)这种语句进行分析。
由于返回的mapper是个代理对象，因此会进入invoke方法，接下来我们来看看MapperProxy的invoke方法。
@Override
public Object invoke(Object proxy, Method method, Object[] args) throws Throwable {
if (Object.class.equals(method.getDeclaringClass())) {
try {
return method.invoke(this, args);
} catch (Throwable t) {
throw ExceptionUtil.unwrapThrowable(t);
}
}
final MapperMethod mapperMethod = cachedMapperMethod(method);
return mapperMethod.execute(sqlSession, args);
}
Object.class.equals(method.getDeclaringClass())的意思是如果定义方法的类是个具体类就使用具体类的实现，如果是接口则往下执行。
private MapperMethod cachedMapperMethod(Method method) {
MapperMethod mapperMethod = methodCache.get(method);
if (mapperMethod == null) {
mapperMethod = new MapperMethod(mapperInterface, method, sqlSession.getConfiguration());
methodCache.put(method, mapperMethod);
}
return mapperMethod;
}
methodCache是个Map<Method, MapperMethod>对象，第一次取时为空会进入MapperMethod构造方法。
public MapperMethod(Class<?> mapperInterface, Method method, Configuration config) {
this.command = new SqlCommand(config, mapperInterface, method);
this.method = new MethodSignature(config, method);
}
public SqlCommand(Configuration configuration, Class<?> mapperInterface, Method method) {
String statementName = mapperInterface.getName() + "." + method.getName();
MappedStatement ms = null;
if (configuration.hasStatement(statementName)) {
ms = configuration.getMappedStatement(statementName);
} else if (!mapperInterface.equals(method.getDeclaringClass())) { // issue #35
String parentStatementName = method.getDeclaringClass().getName() + "." + method.getName();
if (configuration.hasStatement(parentStatementName)) {
ms = configuration.getMappedStatement(parentStatementName);
}
}
if (ms == null) {
if(method.getAnnotation(Flush.class) != null){
name = null;
type = SqlCommandType.FLUSH;
} else {
throw new BindingException("Invalid bound statement (not found): " + statementName);
}
} else {
name = ms.getId();
type = ms.getSqlCommandType();
if (type == SqlCommandType.UNKNOWN) {
throw new BindingException("Unknown execution method for: " + name);
}
}
}
这里主要做了这几件事，根据方法名以及接口名的组合从configuration中取得对应的MappedStatement，然后从中取出name和type。
MethodSignature构造方法如下
public MethodSignature(Configuration configuration, Method method) {
this.returnType = method.getReturnType();
this.returnsVoid = void.class.equals(this.returnType);
this.returnsMany = (configuration.getObjectFactory().isCollection(this.returnType) || this.returnType.isArray());
this.mapKey = getMapKey(method);
this.returnsMap = (this.mapKey != null);
this.hasNamedParameters = hasNamedParams(method);
this.rowBoundsIndex = getUniqueParamIndex(method, RowBounds.class);
this.resultHandlerIndex = getUniqueParamIndex(method, ResultHandler.class);
this.params = Collections.unmodifiableSortedMap(getParams(method, this.hasNamedParameters));
}
这里主要是标记下入参中的RowBounds、ResultHandler类型参数，以及对返回值进行些标记。
MethodSignature与SqlCommand初始化后MapperMethod也就构造完成，然后methodCache将method与mapperMethod关系保留。
接下来就是屌用mapperMethod的execute方法来执行。
public Object execute(SqlSession sqlSession, Object[] args) {
Object result;
if (SqlCommandType.INSERT == command.getType()) {
Object param = method.convertArgsToSqlCommandParam(args);
result = rowCountResult(sqlSession.insert(command.getName(), param));
} else if (SqlCommandType.UPDATE == command.getType()) {
Object param = method.convertArgsToSqlCommandParam(args);
result = rowCountResult(sqlSession.update(command.getName(), param));
} else if (SqlCommandType.DELETE == command.getType()) {
Object param = method.convertArgsToSqlCommandParam(args);
result = rowCountResult(sqlSession.delete(command.getName(), param));
} else if (SqlCommandType.SELECT == command.getType()) {
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 {
Object param = method.convertArgsToSqlCommandParam(args);
result = sqlSession.selectOne(command.getName(), param);
}
} else if (SqlCommandType.FLUSH == command.getType()) {
result = sqlSession.flushStatements();
} else {
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;
}
我们的mapper方法定义如下，返回的不是集合也不为空，因此进入convertArgsToSqlCommandParam方法。
convertArgsToSqlCommandParam对入参进行转换，如果没有入参返回null如果一个入参对象则直接返回，多个入参则封装成个map对象返回。
public Demo getDemo(long id);
现在进入到sqlSession的selectOne方法，使用ibatis的同学应该相当熟悉。
在selectOne内部调用了selectList方法，然后返回集合对象的第一个元素，如果集合对象大于1个则抛错。
@Override
public <E> List<E> selectList(String statement, Object parameter, RowBounds rowBounds) {
try {
MappedStatement ms = configuration.getMappedStatement(statement);
return executor.query(ms, wrapCollection(parameter), rowBounds, Executor.NO_RESULT_HANDLER);
} catch (Exception e) {
throw ExceptionFactory.wrapException("Error querying database. Cause: " + e, e);
} finally {
ErrorContext.instance().reset();
}
}
rowBounds是用来分页的，暂时不管该对象，默认的初始值如下
public static final int NO_ROW_OFFSET = 0;
public static final int NO_ROW_LIMIT = Integer.MAX_VALUE;
selectList也是根据statement从configuration中取得mappedStatement，然后交由executor来执行，sqlSessionFactory构建的时候默认使用的是simpleExecutor
到这里我们分析了mapper接口的方法最终是交到executor来执行。
