首先我们写一个简单spring和mybatis集成的代码如下
public class Test {
public static void main(String[] args){
AnnotationConfigApplicationContext annotationConfigApplicationContext = new AnnotationConfigApplicationContext();
annotationConfigApplicationContext.register(AppConfig.class);
annotationConfigApplicationContext.refresh();
IndexDao indexDao = (IndexDao)annotationConfigApplicationContext.getBean(IndexDao.class);
System.out.println(indexDao.selectAccount());
}
}
public interface IndexDao {
@Select("select * from t_platform_account")
List<TPlatformAccount> selectAccount();
}
@Configuration
@MapperScan("com.fj.log.mapper")
public class AppConfig {
@Bean
public SqlSessionFactoryBean sqlSessionFactoryBean() throws Exception {
SqlSessionFactoryBean factoryBean = new SqlSessionFactoryBean();
factoryBean.setDataSource(dataSource());
return factoryBean;
}
@Bean
public DataSource dataSource(){
DriverManagerDataSource dataSource = new DriverManagerDataSource();
dataSource.setUrl("jdbc:mysql://127.0.0.1:3306/payb?serverTimezone=Hongkong&useUnicode=true&characterEncoding=UTF8&useSSL=false");
dataSource.setDriverClassName("com.mysql.jdbc.Driver");
dataSource.setUsername("root");
dataSource.setPassword("123");
return dataSource;
}
}
这是一个简单的mybatis的应用，我们首先看下我们获取到的indexDao是一个什么对象，org.apache.ibatis.binding.MapperProxy@6ccdb29f可以看出这是一个MapperProxy对象
我们来看下MapperProxy里面的代码是什么
package org.apache.ibatis.binding;
import java.io.Serializable;
import java.lang.invoke.MethodHandles;
import java.lang.invoke.MethodHandles.Lookup;
import java.lang.invoke.MethodType;
import java.lang.reflect.Constructor;
import java.lang.reflect.InvocationHandler;
import java.lang.reflect.Method;
import java.util.Map;
import org.apache.ibatis.reflection.ExceptionUtil;
import org.apache.ibatis.session.SqlSession;
/**
* @author Clinton Begin
* @author Eduardo Macarron
*/
public class MapperProxy<T> implements InvocationHandler, Serializable {
private static final long serialVersionUID = -6424540398559729838L;
private static final int ALLOWED_MODES = MethodHandles.Lookup.PRIVATE | MethodHandles.Lookup.PROTECTED
| MethodHandles.Lookup.PACKAGE | MethodHandles.Lookup.PUBLIC;
private static final Constructor<Lookup> lookupConstructor;
private static final Method privateLookupInMethod;
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;
}
static {
Method privateLookupIn;
try {
privateLookupIn = MethodHandles.class.getMethod("privateLookupIn", Class.class, MethodHandles.Lookup.class);
} catch (NoSuchMethodException e) {
privateLookupIn = null;
}
privateLookupInMethod = privateLookupIn;
Constructor<Lookup> lookup = null;
if (privateLookupInMethod == null) {
// JDK 1.8
try {
lookup = MethodHandles.Lookup.class.getDeclaredConstructor(Class.class, int.class);
lookup.setAccessible(true);
} catch (NoSuchMethodException e) {
throw new IllegalStateException(
"There is neither 'privateLookupIn(Class, Lookup)' nor 'Lookup(Class, int)' method in java.lang.invoke.MethodHandles.",
e);
} catch (Throwable t) {
lookup = null;
}
}
lookupConstructor = lookup;
}
@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 (method.isDefault()) {
if (privateLookupInMethod == null) {
return invokeDefaultMethodJava8(proxy, method, args);
} else {
return invokeDefaultMethodJava9(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) {
return methodCache.computeIfAbsent(method,
k -> new MapperMethod(mapperInterface, method, sqlSession.getConfiguration()));
}
private Object invokeDefaultMethodJava9(Object proxy, Method method, Object[] args)
throws Throwable {
final Class<?> declaringClass = method.getDeclaringClass();
return ((Lookup) privateLookupInMethod.invoke(null, declaringClass, MethodHandles.lookup()))
.findSpecial(declaringClass, method.getName(),
MethodType.methodType(method.getReturnType(), method.getParameterTypes()), declaringClass)
.bindTo(proxy).invokeWithArguments(args);
}
private Object invokeDefaultMethodJava8(Object proxy, Method method, Object[] args)
throws Throwable {
final Class<?> declaringClass = method.getDeclaringClass();
return lookupConstructor.newInstance(declaringClass, ALLOWED_MODES).unreflectSpecial(method, declaringClass)
.bindTo(proxy).invokeWithArguments(args);
}
}
从这里可以看出来这是一个基于jdk动态代理实现代理类那么实际产生调用的时候肯定会进入invoke方法最后肯定会走这个方法
return mapperMethod.execute(sqlSession, args);
好我们再来看看MapperMethod的源代码
public class MapperMethod {
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);
if (method.returnsOptional()
&& (result == null || !method.getReturnType().equals(result.getClass()))) {
result = Optional.ofNullable(result);
}
}
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 (!StatementType.CALLABLE.equals(ms.getStatementType())
&& 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.selectList(command.getName(), param, rowBounds);
} else {
result = sqlSession.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.selectCursor(command.getName(), param, rowBounds);
} else {
result = sqlSession.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.selectMap(command.getName(), param, method.getMapKey(), rowBounds);
} else {
result = sqlSession.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 boolean returnsOptional;
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.returnsOptional = Optional.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;
}
/**
* return whether return type is {@code java.util.Optional}.
* @return return {@code true}, if return type is {@code java.util.Optional}
* @since 3.5.0
*/
public boolean returnsOptional() {
return returnsOptional;
}
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;
}
}
}
重点关注result = sqlSession.selectList(command.getName(), param);这一行代码这个就是真实要去做数据库操作了
前方高能出现，这里会引申出来一个问题就是spring和mybatis结合时为什么mybatis一级缓存会失效，我们先关注下sqlSession具体是什么实现的
SqlSessionTemplate
这个类有个重要的属性在实例化时构造
public SqlSessionTemplate(SqlSessionFactory sqlSessionFactory, ExecutorType executorType,
PersistenceExceptionTranslator exceptionTranslator) {
notNull(sqlSessionFactory, "Property 'sqlSessionFactory' is required");
notNull(executorType, "Property 'executorType' is required");
this.sqlSessionFactory = sqlSessionFactory;
this.executorType = executorType;
this.exceptionTranslator = exceptionTranslator;
this.sqlSessionProxy = (SqlSession) newProxyInstance(SqlSessionFactory.class.getClassLoader(),
new Class[] { SqlSession.class }, new SqlSessionInterceptor());
}
sqlSessionProxy 这个实例是一个代理，所有sql操作都是通过代理实现既然是代理我们关注下
SqlSessionInterceptor的invoke方法
private class SqlSessionInterceptor implements InvocationHandler {
@Override
public Object invoke(Object proxy, Method method, Object[] args) throws Throwable {
SqlSession sqlSession = getSqlSession(SqlSessionTemplate.this.sqlSessionFactory,
SqlSessionTemplate.this.executorType, SqlSessionTemplate.this.exceptionTranslator);
try {
Object result = method.invoke(sqlSession, args);
if (!isSqlSessionTransactional(sqlSession, SqlSessionTemplate.this.sqlSessionFactory)) {
// force commit even on non-dirty sessions because some databases require
// a commit/rollback before calling close()
sqlSession.commit(true);
}
return result;
} catch (Throwable t) {
Throwable unwrapped = unwrapThrowable(t);
if (SqlSessionTemplate.this.exceptionTranslator != null && unwrapped instanceof PersistenceException) {
// release the connection to avoid a deadlock if the translator is no loaded. See issue #22
closeSqlSession(sqlSession, SqlSessionTemplate.this.sqlSessionFactory);
sqlSession = null;
Throwable translated = SqlSessionTemplate.this.exceptionTranslator
.translateExceptionIfPossible((PersistenceException) unwrapped);
if (translated != null) {
unwrapped = translated;
}
}
throw unwrapped;
} finally {
if (sqlSession != null) {
closeSqlSession(sqlSession, SqlSessionTemplate.this.sqlSessionFactory);
}
}
}
}
可以看到在操作结束已经将session关闭了所以一级缓存失效了，这篇文章先写到这里