mybatis源码分析
JDK动态代理
在说mybatis之前，先来了解一下jdk动态代理
/** * 代理类需要实现一个接口java.lang.reflect.InvocationHandler */ public class DynamicProxy implements InvocationHandler { private Object obj; public DynamicProxy() { } public DynamicProxy(Object obj) { this.obj = obj; } @Override public Object invoke(Object proxy, Method method, Object[] args) throws Throwable { System.out.println("before"); if (obj != null) { method.invoke(obj, args); } System.out.println("after"); return null; } }
使用代理
/** * 被代理接口 */ public interface Subject { void request(); }
public static void main(String[] args) { //将动态生成的class文件保存下来，可通过newProxyInstance方法进去查看源码，获得该参数 System.getProperties().put("sun.misc.ProxyGenerator.saveGeneratedFiles", "true"); DynamicProxy dynamicProxy = new DynamicProxy(); Subject subject = (Subject) Proxy.newProxyInstance(Subject.class.getClassLoader(), new Class[]{Subject.class}, dynamicProxy); subject.request(); System.out.println(subject.getClass()); System.out.println(subject.getClass().getSuperclass()); }
生成的class文件，使用反编译器打开
public final class $Proxy0 extends Proxy implements Subject { private static Method m1; private static Method m2; private static Method m3; private static Method m0; public $Proxy0(InvocationHandler var1) throws { super(var1); } public final boolean equals(Object var1) throws { try { return (Boolean)super.h.invoke(this, m1, new Object[]{var1}); } catch (RuntimeException | Error var3) { throw var3; } catch (Throwable var4) { throw new UndeclaredThrowableException(var4); } } public final String toString() throws { try { return (String)super.h.invoke(this, m2, (Object[])null); } catch (RuntimeException | Error var2) { throw var2; } catch (Throwable var3) { throw new UndeclaredThrowableException(var3); } } public final void request() throws { try { super.h.invoke(this, m3, (Object[])null); } catch (RuntimeException | Error var2) { throw var2; } catch (Throwable var3) { throw new UndeclaredThrowableException(var3); } } public final int hashCode() throws { try { return (Integer)super.h.invoke(this, m0, (Object[])null); } catch (RuntimeException | Error var2) { throw var2; } catch (Throwable var3) { throw new UndeclaredThrowableException(var3); } } static { try { m1 = Class.forName("java.lang.Object").getMethod("equals", Class.forName("java.lang.Object")); m2 = Class.forName("java.lang.Object").getMethod("toString"); m3 = Class.forName("com.jvm.byteCode.Subject").getMethod("request"); m0 = Class.forName("java.lang.Object").getMethod("hashCode"); } catch (NoSuchMethodException var2) { throw new NoSuchMethodError(var2.getMessage()); } catch (ClassNotFoundException var3) { throw new NoClassDefFoundError(var3.getMessage()); } } }
start
public class Test { public static void main(String[] args) throws Exception { InputStream in = new FileInputStream("mybatis-config.xml"); SqlSessionFactory factory = new SqlSessionFactoryBuilder().build(in); SqlSession session = factory.openSession(); UserDataManager mapper = session.getMapper(UserDataManager.class); //调用方法 mapper.findGroupsByUser(""); } }
mapper的代理过程
从openSession方法进入
@Override public SqlSession openSession() { return openSessionFromDataSource(configuration.getDefaultExecutorType(), null, false); }
private SqlSession openSessionFromDataSource(ExecutorType execType, TransactionIsolationLevel level, boolean autoCommit) { Transaction tx = null; try { final Environment environment = configuration.getEnvironment(); final TransactionFactory transactionFactory = getTransactionFactoryFromEnvironment(environment); tx = transactionFactory.newTransaction(environment.getDataSource(), level, autoCommit); final Executor executor = configuration.newExecutor(tx, execType); return new DefaultSqlSession(configuration, executor, autoCommit); } catch (Exception e) { closeTransaction(tx); // may have fetched a connection so lets call close() throw ExceptionFactory.wrapException("Error opening session. Cause: " + e, e); } finally { ErrorContext.instance().reset(); } }
public Executor newExecutor(Transaction transaction, ExecutorType executorType) { executorType = executorType == null ? defaultExecutorType : executorType; executorType = executorType == null ? ExecutorType.SIMPLE : executorType; Executor executor; if (ExecutorType.BATCH == executorType) { executor = new BatchExecutor(this, transaction); } else if (ExecutorType.REUSE == executorType) { executor = new ReuseExecutor(this, transaction); } else { executor = new SimpleExecutor(this, transaction); } if (cacheEnabled) { executor = new CachingExecutor(executor); } executor = (Executor) interceptorChain.pluginAll(executor);//Executor也可以被拦截器拦截 return executor; }
从getMapper方法进入
@Override public <T> T getMapper(Class<T> type) { return configuration.<T>getMapper(type, this); }
public <T> T getMapper(Class<T> type, SqlSession sqlSession) { return mapperRegistry.getMapper(type, sqlSession); }
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); } }
protected T newInstance(MapperProxy<T> mapperProxy) { return (T) Proxy.newProxyInstance(mapperInterface.getClassLoader(), new Class[] { mapperInterface }, mapperProxy); } public T newInstance(SqlSession sqlSession) { final MapperProxy<T> mapperProxy = new MapperProxy<T>(sqlSession, mapperInterface, methodCache); return newInstance(mapperProxy); }
public class MapperProxy<T> implements InvocationHandler, Serializable { private static final long serialVersionUID = -6424540398559729838L; private final SqlSession sqlSession; private final Class<T> mapperInterface; private final Map<Method, MapperMethod> methodCache; public MapperProxy(SqlSession sqlSession, Class<T> mapperInterface, Map<Method, MapperMethod> methodCache) { this.sqlSession = sqlSession; this.mapperInterface = mapperInterface; this.methodCache = methodCache; } @Override public Object invoke(Object proxy, Method method, Object[] args) throws Throwable { try { if (Object.class.equals(method.getDeclaringClass())) { return method.invoke(this, args); } else if (isDefaultMethod(method)) { return invokeDefaultMethod(proxy, method, args); } } catch (Throwable t) { throw ExceptionUtil.unwrapThrowable(t); } final MapperMethod mapperMethod = cachedMapperMethod(method); return mapperMethod.execute(sqlSession, args); } 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; } @UsesJava7 private Object invokeDefaultMethod(Object proxy, Method method, Object[] args) throws Throwable { final Constructor<MethodHandles.Lookup> constructor = MethodHandles.Lookup.class .getDeclaredConstructor(Class.class, int.class); if (!constructor.isAccessible()) { constructor.setAccessible(true); } final Class<?> declaringClass = method.getDeclaringClass(); return constructor .newInstance(declaringClass, MethodHandles.Lookup.PRIVATE | MethodHandles.Lookup.PROTECTED | MethodHandles.Lookup.PACKAGE | MethodHandles.Lookup.PUBLIC) .unreflectSpecial(method, declaringClass).bindTo(proxy).invokeWithArguments(args); } /** * Backport of java.lang.reflect.Method#isDefault() */ private boolean isDefaultMethod(Method method) { return ((method.getModifiers() & (Modifier.ABSTRACT | Modifier.PUBLIC | Modifier.STATIC)) == Modifier.PUBLIC) && method.getDeclaringClass().isInterface(); } }
public Object execute(SqlSession sqlSession, Object[] args) { Object result; switch (command.getType()) { case INSERT: { Object param = method.convertArgsToSqlCommandParam(args);
//以insert方法为例 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; }
@Override public int insert(String statement, Object parameter) { return update(statement, parameter); }
@Override public int update(String statement, Object parameter) { try { dirty = true; MappedStatement ms = configuration.getMappedStatement(statement); return executor.update(ms, wrapCollection(parameter)); } catch (Exception e) { throw ExceptionFactory.wrapException("Error updating database. Cause: " + e, e); } finally { ErrorContext.instance().reset(); } }
@Override public int update(MappedStatement ms, Object parameter) throws SQLException { ErrorContext.instance().resource(ms.getResource()).activity("executing an update").object(ms.getId()); if (closed) { throw new ExecutorException("Executor was closed."); } clearLocalCache(); return doUpdate(ms, parameter); }
@Override public int doUpdate(MappedStatement ms, Object parameter) throws SQLException { Statement stmt = null; try { Configuration configuration = ms.getConfiguration(); StatementHandler handler = configuration.newStatementHandler(this, ms, parameter, RowBounds.DEFAULT, null, null); stmt = prepareStatement(handler, ms.getStatementLog()); return handler.update(stmt); } finally { closeStatement(stmt); } }
public StatementHandler newStatementHandler
(Executor executor, MappedStatement mappedStatement, Object parameterObject, RowBounds rowBounds, ResultHandler resultHandler, BoundSql boundSql) { StatementHandler statementHandler = new RoutingStatementHandler(executor, mappedStatement, parameterObject, rowBounds, resultHandler, boundSql); statementHandler = (StatementHandler) interceptorChain.pluginAll(statementHandler);//StatementHandler是可以通过mybatis拦截器进行拦截的 return statementHandler; }
public SimpleStatementHandler
(Executor executor, MappedStatement mappedStatement, Object parameter, RowBounds rowBounds, ResultHandler resultHandler, BoundSql boundSql) { super(executor, mappedStatement, parameter, rowBounds, resultHandler, boundSql); } @Override public int update(Statement statement) throws SQLException { String sql = boundSql.getSql(); Object parameterObject = boundSql.getParameterObject(); KeyGenerator keyGenerator = mappedStatement.getKeyGenerator(); int rows; if (keyGenerator instanceof Jdbc3KeyGenerator) { statement.execute(sql, Statement.RETURN_GENERATED_KEYS); rows = statement.getUpdateCount(); keyGenerator.processAfter(executor, mappedStatement, statement, parameterObject); } else if (keyGenerator instanceof SelectKeyGenerator) { statement.execute(sql); rows = statement.getUpdateCount(); keyGenerator.processAfter(executor, mappedStatement, statement, parameterObject); } else { statement.execute(sql); rows = statement.getUpdateCount(); } return rows; }
protected BaseStatementHandler
(Executor executor, MappedStatement mappedStatement, Object parameterObject, RowBounds rowBounds, ResultHandler resultHandler, BoundSql boundSql) { this.configuration = mappedStatement.getConfiguration(); this.executor = executor; this.mappedStatement = mappedStatement; this.rowBounds = rowBounds; this.typeHandlerRegistry = configuration.getTypeHandlerRegistry(); this.objectFactory = configuration.getObjectFactory(); if (boundSql == null) { // issue #435, get the key before calculating the statement generateKeys(parameterObject); boundSql = mappedStatement.getBoundSql(parameterObject); } this.boundSql = boundSql; this.parameterHandler = configuration.newParameterHandler(mappedStatement, parameterObject, boundSql); this.resultSetHandler = configuration.newResultSetHandler(executor, mappedStatement, rowBounds, parameterHandler, resultHandler, boundSql); }
public ParameterHandler newParameterHandler(MappedStatement mappedStatement, Object parameterObject, BoundSql boundSql) { ParameterHandler parameterHandler = mappedStatement.getLang().createParameterHandler(mappedStatement, parameterObject, boundSql); parameterHandler = (ParameterHandler) interceptorChain.pluginAll(parameterHandler);//ParameterHandler可以被拦截器拦截 return parameterHandler; } public ResultSetHandler newResultSetHandler(Executor executor, MappedStatement mappedStatement, RowBounds rowBounds, ParameterHandler parameterHandler, ResultHandler resultHandler, BoundSql boundSql) { ResultSetHandler resultSetHandler = new DefaultResultSetHandler(executor, mappedStatement, parameterHandler, resultHandler, boundSql, rowBounds); resultSetHandler = (ResultSetHandler) interceptorChain.pluginAll(resultSetHandler);//ResultSetHandler可以被拦截器拦截 return resultSetHandler; }
//JDBC操作
@Override public int update(Statement statement) throws SQLException { String sql = boundSql.getSql(); Object parameterObject = boundSql.getParameterObject(); KeyGenerator keyGenerator = mappedStatement.getKeyGenerator(); int rows; if (keyGenerator instanceof Jdbc3KeyGenerator) { statement.execute(sql, Statement.RETURN_GENERATED_KEYS); rows = statement.getUpdateCount(); keyGenerator.processAfter(executor, mappedStatement, statement, parameterObject); } else if (keyGenerator instanceof SelectKeyGenerator) { statement.execute(sql); rows = statement.getUpdateCount(); keyGenerator.processAfter(executor, mappedStatement, statement, parameterObject); } else { statement.execute(sql); rows = statement.getUpdateCount(); } return rows; }
由此我们可以看出mybatis的mapper接口时通过MapperProxy类进行代理执行的，然后一层一层封装，最后有JDBC实现数据处理
mybatis拦截器
继续查看源码，以Executor为例
executor = (Executor) interceptorChain.pluginAll(executor);
public Object pluginAll(Object target) { for (Interceptor interceptor : interceptors) { target = interceptor.plugin(target); } return target; }
@Override public Object plugin(Object target) { return Plugin.wrap(target, this); }
public class Plugin implements InvocationHandler { private final Object target; private final Interceptor interceptor; private final Map<Class<?>, Set<Method>> signatureMap; private Plugin(Object target, Interceptor interceptor, Map<Class<?>, Set<Method>> signatureMap) { this.target = target; this.interceptor = interceptor; this.signatureMap = signatureMap; } public static Object wrap(Object target, Interceptor interceptor) { Map<Class<?>, Set<Method>> signatureMap = getSignatureMap(interceptor);//获取该拦截器可以拦截的接口和方法 Class<?> type = target.getClass(); Class<?>[] interfaces = getAllInterfaces(type, signatureMap);//获取该拦截器可以拦截的接口 if (interfaces.length > 0) {//存在可以拦截的接口，则使用jdk动态代理生成对应的代理实例 return Proxy.newProxyInstance( type.getClassLoader(), interfaces, new Plugin(target, interceptor, signatureMap)); } return target; } @Override public Object invoke(Object proxy, Method method, Object[] args) throws Throwable { try { Set<Method> methods = signatureMap.get(method.getDeclaringClass()); if (methods != null && methods.contains(method)) {//允许被拦截的方法会执行拦截器对应的intercept方法 return interceptor.intercept(new Invocation(target, method, args)); } return method.invoke(target, args);//链式调用 } catch (Exception e) { throw ExceptionUtil.unwrapThrowable(e); } } private static Map<Class<?>, Set<Method>> getSignatureMap(Interceptor interceptor) { Intercepts interceptsAnnotation = interceptor.getClass().getAnnotation(Intercepts.class); // issue #251 if (interceptsAnnotation == null) { throw new PluginException("No @Intercepts annotation was found in interceptor " + interceptor.getClass().getName()); } Signature[] sigs = interceptsAnnotation.value(); Map<Class<?>, Set<Method>> signatureMap = new HashMap<Class<?>, Set<Method>>(); for (Signature sig : sigs) { Set<Method> methods = signatureMap.get(sig.type()); if (methods == null) { methods = new HashSet<Method>(); signatureMap.put(sig.type(), methods); } try { Method method = sig.type().getMethod(sig.method(), sig.args()); methods.add(method); } catch (NoSuchMethodException e) { throw new PluginException("Could not find method on " + sig.type() + " named " + sig.method() + ". Cause: " + e, e); } } return signatureMap; } private static Class<?>[] getAllInterfaces(Class<?> type, Map<Class<?>, Set<Method>> signatureMap) { Set<Class<?>> interfaces = new HashSet<Class<?>>(); while (type != null) { for (Class<?> c : type.getInterfaces()) { if (signatureMap.containsKey(c)) { interfaces.add(c); } } type = type.getSuperclass(); } return interfaces.toArray(new Class<?>[interfaces.size()]); } }
由上面源码分析可以看出，如果我们为Executor写3个拦截器，分别时A、B、C，代理顺序是Executor被A代理、A被B代理、C被B代理，这种设计模式就叫做责任链模式
mybatis插件
import org.apache.ibatis.executor.statement.StatementHandler; import org.apache.ibatis.plugin.*; import java.sql.Connection; import java.util.Properties; @Intercepts(@Signature( type = StatementHandler.class,//代理的接口 method = "prepare",//代理的方法 args = {Connection.class, Integer.class}//方法参数信息 )) public class PagePlugin implements Interceptor { @Override public Object intercept(Invocation invocation) throws Throwable { //TODO 可以添加自己的逻辑代码，分页等信息 return invocation.proceed(); } @Override public Object plugin(Object target) { return Plugin.wrap(target, this); } @Override public void setProperties(Properties properties) { //可以获取到mybatis配置文件中的参数信息 } }
