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0開(kāi)始代碼AuthorMapper mapper = session.getMapper(AuthorMapper.class);
1 DefaultSqlSession類(lèi)
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public <T> T getMapper(Class<T> type) {
//最后會(huì)去調(diào)用MapperRegistry.getMapper
return configuration.<T>getMapper(type, this);
}
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2 Configuration類(lèi)
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public <T> T getMapper(Class<T> type, SqlSession sqlSession) {
return mapperRegistry.getMapper(type, sqlSession);
}
3 MapperRegistry類(lèi)
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//返回代理類(lèi)
public <T> T getMapper(Class<T> type, SqlSession sqlSession) {
final MapperProxyFactory<T> mapperProxyFactory = (MapperProxyFactory<T>) knownMappers.get(type);
if (mapperProxyFactory == null) {
throw new BindingException("Type " + type + " is not known to the MapperRegistry.");
}
try {
return mapperProxyFactory.newInstance(sqlSession);
} catch (Exception e) {
throw new BindingException("Error getting mapper instance. Cause: " + e, e);
}
}
MapperProxyFactory<T> 類(lèi)
public T newInstance(SqlSession sqlSession) {
final MapperProxy<T> mapperProxy = new MapperProxy<T>(sqlSession, mapperInterface, methodCache);
return newInstance(mapperProxy);
}
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protected T newInstance(MapperProxy<T> mapperProxy) {
//用JDK自帶的動(dòng)態(tài)代理生成映射器
return (T) Proxy.newProxyInstance(mapperInterface.getClassLoader(), new Class[] { mapperInterface }, mapperProxy);
}
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MapperProxy類(lèi)
public class MapperProxy<T> implements InvocationHandler, Serializable{
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public MapperProxy(SqlSession sqlSession, Class<T> mapperInterface, Map<Method, MapperMethod> methodCache) {
this.sqlSession = sqlSession;
this.mapperInterface = mapperInterface;
this.methodCache = methodCache;
}
}
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//去緩存中找MapperMethod
private MapperMethod cachedMapperMethod(Method method) {
MapperMethod mapperMethod = methodCache.get(method);
if (mapperMethod == null) {
//找不到才去new
mapperMethod = new MapperMethod(mapperInterface, method, sqlSession.getConfiguration());
methodCache.put(method, mapperMethod);
}
return mapperMethod;
}
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public Object invoke(Object proxy, Method method, Object[] args) throws Throwable {
//代理以后，所有Mapper的方法調(diào)用時(shí)，都會(huì)調(diào)用這個(gè)invoke方法
//并不是任何一個(gè)方法都需要執(zhí)行調(diào)用代理對(duì)象進(jìn)行執(zhí)行，如果這個(gè)方法是Object中通用的方法（toString、hashCode等）無(wú)需執(zhí)行
if (Object.class.equals(method.getDeclaringClass())) {
try {
return method.invoke(this, args);
} catch (Throwable t) {
throw ExceptionUtil.unwrapThrowable(t);
}
}
//這里優(yōu)化了，去緩存中找MapperMethod
final MapperMethod mapperMethod = cachedMapperMethod(method);
//執(zhí)行
return mapperMethod.execute(sqlSession, args);
}
MapperMethod類(lèi)
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//執(zhí)行
public Object execute(SqlSession sqlSession, Object[] args) {
Object result;
//可以看到執(zhí)行時(shí)就是4種情況，insert|update|delete|select，分別調(diào)用SqlSession的4大類(lèi)方法
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()) {
//如果有結(jié)果處理器
executeWithResultHandler(sqlSession, args);
result = null;
} else if (method.returnsMany()) {
//如果結(jié)果有多條記錄
result = executeForMany(sqlSession, args);
} else if (method.returnsMap()) {
//如果結(jié)果是map
result = executeForMap(sqlSession, args);
} else {
//否則就是一條記錄
Object param = method.convertArgsToSqlCommandParam(args);
result = sqlSession.selectOne(command.getName(), param);
}
} 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;
}
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