Mybatis接口编程原理分析

1、Mybatis接口编程原理分析Mybatis接口编程相关的类主要有MapperProxyFactory、MapperProxy、MapperMethod和MapperRegister四个类：MapperProxyFactory：通过类名我们可以猜到这是一个MapperProxy的工厂类，用于创建MapperProxy的，通过函数newInstance(SqlSession sqlSession)来创建MapperProxy的代理类。源码如下：java view plain copy print?在CODE上查看代码片派生到我的代码片/这个类赋值创建具体mapper接口代理对象的工厂 publi

2、c class MapperProxyFactory<T> /具体Mapper接口的class对象 private final Class<T> mapperInterface; /该接口下面的缓存，key是方法对象，value是对接口中方法对象的封装 private final Map<Method, MapperMethod> methodCache = new ConcurrentHashMap<Method, MapperMethod>(); public MapperProxyFactory(Class<T> mapperI

3、nterface) this.mapperInterface = mapperInterface; public Class<T> getMapperInterface() return mapperInterface; public Map<Method, MapperMethod> getMethodCache() return methodCache; SuppressWarnings("unchecked") protected T newInstance(MapperProxy<T> mapperProxy) /创建一个代理类并

4、返回 return (T) Proxy.newProxyInstance(mapperInterface.getClassLoader(), new Class mapperInterface , mapperProxy); public T newInstance(SqlSession sqlSession) /在这里创建MapperProxy对象，这个类实现了JDK的动态代理接口 InvocationHandler final MapperProxy<T> mapperProxy = new MapperProxy<T>(sqlSession, mapperInte

5、rface, methodCache); /调用上面的方法，返回一个接口的代理类 return newInstance(mapperProxy); MapperProxy：通过类名可以猜到这个类为一个代理类，它实现了JDK动态代理接口InvocationHandler，通过查看源码发现它又不像一个真正的代理类，它一般不会真正执行被代理类的函数方法，只是在执行被代理类函数方法时来执行MapperMethod类的execute方法，具体逻辑详看invoke函数源码如下：java view plain copy print?在CODE上查看代码片派生到我的代码片/实现了JDK动态代理的接口，Invo

6、cationHandler /在invoke方法中实现了代理方法调用的细节 public class MapperProxy<T> implements InvocationHandler, Serializable private static final long serialVersionUID = -6424540398559729838L; /sqlSession private final SqlSession sqlSession; /接口的类型对象 private final Class<T> mapperInterface; /接口中方法的缓存，由Ma

7、pperProxyFactory传递过来 private final Map<Method, MapperMethod> methodCache; /构造函数 public MapperProxy(SqlSession sqlSession, Class<T> mapperInterface, Map<Method, MapperMethod> methodCache) this.sqlSession = sqlSession; this.mapperInterface = mapperInterface; this.methodCache = method

8、Cache; /接口代理对象所有的方法调用都会调用该方法 Override public Object invoke(Object proxy, Method method, Object args) throws Throwable /判断是不是基础方法比如toString、hashCode等，这些方法直接调用不需要处理 if (Object.class.equals(method.getDeclaringClass() try return method.invoke(this, args); catch (Throwable t) throw ExceptionUtil.unwrapTh

9、rowable(t); /进行缓存 final MapperMethod mapperMethod = cachedMapperMethod(method); /调用mapperMethod.execute 核心的地方就在这个方法里，这个方法对才是真正对SqlSession进行的包装调用 return mapperMethod.execute(sqlSession, args); /缓存处理 private MapperMethod cachedMapperMethod(Method method) MapperMethod mapperMethod = methodCache.get(met

10、hod); if (mapperMethod = null) mapperMethod = new MapperMethod(mapperInterface, method, sqlSession.getConfiguration(); methodCache.put(method, mapperMethod); return mapperMethod; MapperMethod：它是mybatis接口编程的核心，它封装了对sqlsession的操作，mybatis接口编程的实质还是sqlsession进行的CRUD操作通过分析下面的源码我们可以了解到mybatis接口编程的实质还是sqlse

11、ssion进行CRUD操作，接口编程不过是通过代理获得接口和函数名作为xml文件中的映射ID，获得接口函数的参数值作为sqlsession操作的参数值而已，所以mybatis的接口编程原理还是比较简单的。源码如下：java view plain copy print?/* * author Clinton Begin * author Eduardo Macarron * author Lasse Voss */ /这个类是整个代理机制的核心类，对Sqlsession当中的操作进行了封装 public class MapperMethod /一个内部封 封装了SQL标签的类型 insert u

12、pdate delete select private final SqlCommand command; /一个内部类 封装了方法的参数信息 返回类型信息等 private final MethodSignature method; /构造参数 public MapperMethod(Class<?> mapperInterface, Method method, Configuration config) mand = new SqlCommand(config, mapperInterface, method); this.method = new MethodSignatu

13、re(config, method); /这个方法是对SqlSession的包装调用 public Object execute(SqlSession sqlSession, Object args) /定义返回结果 Object result; /如果是INSERT操作 if (SqlCommandType.INSERT = command.getType() /处理参数 Object param = method.convertArgsToSqlCommandParam(args); /调用sqlSession的insert方法 result = rowCountResult(sqlSes

14、sion.insert(command.getName(), param); /如果是UPDATE操作 同上 else if (SqlCommandType.UPDATE = command.getType() Object param = method.convertArgsToSqlCommandParam(args); result = rowCountResult(sqlSession.update(command.getName(), param); /如果是DELETE操作 同上 else if (SqlCommandType.DELETE = command.getType()

15、Object param = method.convertArgsToSqlCommandParam(args); result = rowCountResult(sqlSession.delete(command.getName(), param); /如果是SELECT操作 那么情况会多一些 但是也都和sqlSession的查询方法一一对应 else if (SqlCommandType.SELECT = command.getType() /如果返回void 并且参数有resultHandler /则调用 void select(String statement, Object para

16、meter, ResultHandler handler);方法 if (method.returnsVoid() && method.hasResultHandler() executeWithResultHandler(sqlSession, args); result = null; /如果返回多行结果这调用 <E> List<E> selectList(String statement, Object parameter); /executeForMany这个方法调用的 else if (method.returnsMany() result =

17、 executeForMany(sqlSession, args); /如果返回类型是MAP 则调用executeForMap方法 else if (method.returnsMap() result = executeForMap(sqlSession, args); else /否则就是查询单个对象 Object param = method.convertArgsToSqlCommandParam(args); result = sqlSession.selectOne(command.getName(), param); else if (SqlCommandType.FLUSH =

18、 command.getType() result = sqlSession.flushStatements(); else /如果全都不匹配 说明mapper中定义的方法不对 throw new BindingException("Unknown execution method for: " + command.getName(); /如果返回值为空 并且方法返回值类型是基础类型 并且不是VOID 则抛出异常 if (result = null && method.getReturnType().isPrimitive() && !met

19、hod.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 re

20、sult; if (method.returnsVoid() result = null; else if (Integer.class.equals(method.getReturnType() | Integer.TYPE.equals(method.getReturnType() result = Integer.valueOf(rowCount); else if (Long.class.equals(method.getReturnType() | Long.TYPE.equals(method.getReturnType() result = Long.valueOf(rowCou

21、nt); else if (Boolean.class.equals(method.getReturnType() | Boolean.TYPE.equals(method.getReturnType() result = Boolean.valueOf(rowCount > 0); else throw new BindingException("Mapper method '" + command.getName() + "' has an unsupported return type: " + method.getRetur

22、nType(); 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 " + comman

23、d.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.e

24、xtractRowBounds(args); sqlSession.select(command.getName(), param, rowBounds, method.extractResultHandler(args); else sqlSession.select(command.getName(), param, method.extractResultHandler(args); /返回多行结果 调用sqlSession.selectList方法 private <E> Object executeForMany(SqlSession sqlSession, Object

25、 args) List<E> result; Object param = method.convertArgsToSqlCommandParam(args); /如果参数含有rowBounds则调用分页的查询 if (method.hasRowBounds() RowBounds rowBounds = method.extractRowBounds(args); result = sqlSession.<E>selectList(command.getName(), param, rowBounds); else /没有分页则调用普通查询 result = sqlS

26、ession.<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()

27、, result); 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;

28、SuppressWarnings("unchecked") private <E> E convertToArray(List<E> list) E array = (E) Array.newInstance(method.getReturnType().getComponentType(), list.size(); array = list.toArray(array); return array; private <K, V> Map<K, V> executeForMap(SqlSession sqlSession,

29、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.&

30、lt;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 Binding

31、Exception("Parameter '" + key + "' not found. Available parameters are " + keySet(); return super.get(key); /一个内部类 封装了具体执行的动作 public static class SqlCommand /xml标签的id private final String name; /insert update delete select的具体类型 private final SqlCommandType type; public Sq

32、lCommand(Configuration configuration, Class<?> mapperInterface, Method method) /拿到全名 接口名加上方法名 String statementName = mapperInterface.getName() + "." + method.getName(); MappedStatement ms = null; /获取MappedStatement对象 这个对象封装了XML当中一个标签的所有信息 比如下面 /<select id="selectBlog" re

33、sultType="Blog"> /select * from Blog where id = #id /</select> if (configuration.hasStatement(statementName) ms = configuration.getMpedStatement(statementName); else if (!mapperInterface.equals(method.getDeclaringClass() / issue #35 String parentStatementName = method.getDeclaring

34、Class().getName() + "." + method.getName(); if (configuration.hasStatement(parentStatementName) ms = configuration.getMappedStatement(parentStatementName); /为空抛出异常 if (ms = null) if(method.getAnnotation(Flush.class) != null) name = null; type = SqlCommandType.FLUSH; else throw new BindingE

35、xception("Invalid bound statement (not found): " + statementName); else name = ms.getId(); type = ms.getSqlCommandType(); /判断SQL标签类型 未知就抛异常 if (type = SqlCommandType.UNKNOWN) throw new BindingException("Unknown execution method for: " + name); public String getName() return name;

36、 public SqlCommandType getType() return type; /内部类 封装了接口当中方法的 参数类型 返回值类型 等信息 public static class MethodSignature /是否返回多调结果 private final boolean returnsMany; /返回值是否是MAP private final boolean returnsMap; /返回值是否是VOID private final boolean returnsVoid; /返回值类型 private final Class<?> returnType; /m

37、apKey private final String mapKey; /resultHandler类型参数的位置 private final Integer resultHandlerIndex; /rowBound类型参数的位置 private final Integer rowBoundsIndex; /用来存放参数信息 private final SortedMap<Integer, String> params; /是否存在命名参数 private final boolean hasNamedParameters; public MethodSignature(Config

38、uration 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 = (t

39、his.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.hasNamedParame

40、ters); public Object convertArgsToSqlCommandParam(Object args) final int paramCount = params.size(); if (args = null | paramCount = 0) return null; else if (!hasNamedParameters && paramCount = 1) return argsparams.keySet().iterator().next().intValue(); else final Map<String, Object> pa

41、ram = new ParamMap<Object>(); int i = 0; for (Map.Entry<Integer, String> entry : params.entrySet() param.put(entry.getValue(), argsentry.getKey().intValue(); / issue #71, add param names as param1, param2.but ensure backward compatibility final String genericParamName = "param"

42、 + String.valueOf(i + 1); if (!param.containsKey(genericParamName) param.put(genericParamName, argsentry.getKey(); i+; return param; public boolean hasRowBounds() return rowBoundsIndex != null; public RowBounds extractRowBounds(Object args) return hasRowBounds() ? (RowBounds) argsrowBoundsIndex : nu

43、ll; public boolean hasResultHandler() return resultHandlerIndex != null; public ResultHandler extractResultHandler(Object args) return hasResultHandler() ? (ResultHandler) argsresultHandlerIndex : null; public String getMapKey() return mapKey; public Class<?> getReturnType() return returnType;

44、 public boolean returnsMany() return returnsMany; public boolean returnsMap() return returnsMap; public boolean returnsVoid() return returnsVoid; 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(argTypesi) if (index = null) index = i; else throw new Bindin