架构学习资料
由于篇幅限制小编，pdf文档的详解资料太全面，细节内容实在太多啦，所以只把部分知识点截图出来粗略的介绍，每个小节点里面都有更细化的内容！
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需要这份系统化的资料的朋友，可以点击这里获取
throw new BuilderException(“A mapper element may only specify a url, resource or class, but not more than one.”);
}
}
}
}
}
}
我的UserMapper.xml文件内容为：
<?xml version="1.0" encoding="UTF-8"?> select * from `user` where userId = #{userId}UserMapper接口内容为：
package com.mapper;
import com.entity.User;
import org.apache.ibatis.annotations.Select;
public interface UserMapper {
@Select(“select * from where userId = 2”)
User findById(int userId);
}
疑问？UserMapper.xml有<select id=“findById”，而在接口中的findById方法我又加了一个@Select注解；那么执行会选择哪一条Sql执行还是报错呢？
public class XMLMapperBuilder extends BaseBuilder {
public void parse() {
if (!configuration.isResourceLoaded(resource)) {
bindMapperForNamespace();
}
parsePendingResultMaps();
parsePendingCacheRefs();
parsePendingStatements();
}
}
解析 mapper.xml文件内容
public class XMLMapperBuilder extends BaseBuilder {
private void configurationElement(XNode context) {
try {
buildStatementFromContext(context.evalNodes(“select|insert|update|delete”));
} catch (Exception e) {
throw new BuilderException(“Error parsing Mapper XML. The XML location is '” + resource + "'. Cause: " + e, e);
}
}
}
builderAssistant.addMappedStatement,并不是添加一个mapper.xml文件隐射的实例，而是为每一个Sql语句创建一个实例
public class XMLStatementBuilder extends BaseBuilder {
private final MapperBuilderAssistant builderAssistant;
public void parseStatementNode() {
builderAssistant.addMappedStatement(id, sqlSource, statementType, sqlCommandType,
fetchSize, timeout, parameterMap, parameterTypeClass, resultMap, resultTypeClass,
resultSetTypeEnum, flushCache, useCache, resultOrdered,
keyGenerator, keyProperty, keyColumn, databaseId, langDriver, resultSets);
}
}
创建一个MappedStatement实例添加到 Configuration.mappedStatements的Map集合中
public class XMLStatementBuilder extends BaseBuilder {
public MappedStatement addMappedStatement() {
ParameterMap statementParameterMap = getStatementParameterMap(parameterMap, parameterType, id);
if (statementParameterMap != null) {
statementBuilder.parameterMap(statementParameterMap);
}
MappedStatement statement = statementBuilder.build();
configuration.addMappedStatement(statement);
return statement;
}
}
开始解析接口注解，并添加一个MapperProxyFactory代理工厂的对象到configuration.mapperRegistry.knownMappers；key是Mapper接口
public class XMLMapperBuilder extends BaseBuilder {
private void bindMapperForNamespace() {
String namespace = builderAssistant.getCurrentNamespace();
if (namespace != null) {
Class<?> boundType = null;
try {
configuration.addMapper(boundType);
}
}
}
}
}
public class Configuration {
protected final MapperRegistry mapperRegistry = new MapperRegistry(this);
public void addMapper(Class type) {
mapperRegistry.addMapper(type);
}
}
mapperRegistry.addMapper(type)；
为Mapper接口创建一个代理工厂，方便后期使用Mapper接口时创建代理类
解析mapper接口的注解信息
public class MapperRegistry {
public void addMapper(Class type) {
if (type.isInterface()) {
if (hasMapper(type)) {
throw new BindingException(“Type " + type + " is already known to the MapperRegistry.”);
}
boolean loadCompleted = false;
try {
parser.parse();
loadCompleted = true;
} finally {
if (!loadCompleted) {
knownMappers.remove(type);
}
}
}
}
}
解析mapper接口的注解信息，parseStatement(method)主要在这个方法中完成
public class MapperAnnotationBuilder {
public void parse() {
String resource = type.toString();
if (!configuration.isResourceLoaded(resource)) {
loadXmlResource();
configuration.addLoadedResource(resource);
assistant.setCurrentNamespace(type.getName());
parsePendingMethods();
}
}
创建一个MappedStatement实例添加到 Configuration.mappedStatements的Map集合中
public class MapperAnnotationBuilder {
private final MapperBuilderAssistant assistant;
void parseStatement(Method method) {
assistant.addMappedStatement(
mappedStatementId,
sqlSource,
statementType,
sqlCommandType,
fetchSize,
timeout,
// ParameterMapID
null,
parameterTypeClass,
resultMapId,
getReturnType(method),
resultSetType,
flushCache,
useCache,
// TODO gcode issue #577
false,
keyGenerator,
keyProperty,
keyColumn,
// DatabaseID
null,
languageDriver,
// ResultSets
options != null ? nullOrEmpty(options.resultSets()) : null);
}
}
这里重点分析Configuration.addMappedStatement(statement);在做什么操作，并且解决 1.4.2留下的疑点；UserMapper.xml和UserMapper接口都有findById的Sql语句定义
public class Configuration {
public void addMappedStatement(MappedStatement ms) {
mappedStatements.put(ms.getId(), ms);
}
}
mappedStatements.put(ms.getId(), ms); 实际调用 Configuration.StrictMap.put()方法
Configuration.StrictMap是一个重写的HashMap，put方法会先校验key是否存在
public class Configuration {
protected final Map<String, MappedStatement> mappedStatements = new Configuration.StrictMap(“Mapped Statements collection”)
.conflictMessageProducer((savedValue, targetValue) ->
". please check " + savedValue.getResource() + " and " + targetValue.getResource());
protected static class StrictMap extends HashMap<String, V> {
@Override
@SuppressWarnings(“unchecked”)
public V put(String key, V value) {
if (containsKey(key)) {
throw new IllegalArgumentException(name + " already contains value for " + key
- (conflictMessageProducer == null ? “” : conflictMessageProducer.apply(super.get(key), value)));
}
if (key.contains(“.”)) {
final String shortKey = getShortName(key);
if (super.get(shortKey) == null) {
super.put(shortKey, value);
} else {
super.put(shortKey, (V) new org.apache.ibatis.session.Configuration.StrictMap.Ambiguity(shortKey));
}
}
return super.put(key, value);
}
}
}
public class Main {
public static void main(String[] args) throws IOException {
String configName = “mybatis_config.xml”;
Reader reader = Resources.getResourceAsReader(configName);
SqlSessionFactory sqlSessionFactory = new SqlSessionFactoryBuilder().build(reader);
SqlSession sqlSession = sqlSessionFactory.openSession();
UserMapper userMapper = sqlSession.getMapper(UserMapper.class);
User user = userMapper.findById(1);
System.out.println(user);
}
}
输出结果：User{userId=1, username=‘张三’, sex=‘男’, age=12}
一行代码的查询，底层既然走了那么多流程；
调用DefaultSqlSessionFactory.openSessionFromDataSource();
public class DefaultSqlSessionFactory implements SqlSessionFactory {
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 class Configuration {
public Executor newExecutor(Transaction transaction, ExecutorType executorType) {
executorType = executorType == null ? defaultExecutorType : executorType;
executorType = executorType == null ? ExecutorType.SIMPLE : executorType;
Executor executor;
if (ExecutorType.BATCH == executorType) {
if (cacheEnabled) {
executor = new CachingExecutor(executor);
}
executor = (Executor) interceptorChain.pluginAll(executor);
return executor;
}
}
获取Mapper接口代理类实例
public class DefaultSqlSession implements SqlSession {
@Override
public T getMapper(Class type) {
return configuration.getMapper(type, this);
}
}
public class Configuration {
public T getMapper(Class type, SqlSession sqlSession) {
return mapperRegistry.getMapper(type, sqlSession);
}
}
public class MapperRegistry {
private final Configuration config;
private final Map<Class<?>, MapperProxyFactory<?>> knownMappers = new HashMap<>();
public T getMapper(Class type, SqlSession sqlSession) {
return mapperProxyFactory.newInstance(sqlSession);
} catch (Exception e) {
throw new BindingException("Error getting mapper instance. Cause: " + e, e);
}
}
}
InvocationHandler是MapperProxy
public class MapperProxyFactory {
private final Class mapperInterface;
private final Map<Method, MapperMethod> methodCache = new ConcurrentHashMap<>();
public MapperProxyFactory(Class mapperInterface) {
this.mapperInterface = mapperInterface;
}
@SuppressWarnings(“unchecked”)
protected T newInstance(MapperProxy mapperProxy) {
return (T) Proxy.newProxyInstance(mapperInterface.getClassLoader(), new Class[] { mapperInterface }, mapperProxy);
}
public T newInstance(SqlSession sqlSession) {
final MapperProxy mapperProxy = new MapperProxy<>(sqlSession, mapperInterface, methodCache);
return newInstance(mapperProxy);
}
}
会走代理类 MapperProxy.invoke
public class MapperProxy implements InvocationHandler, Serializable {
private static final long serialVersionUID = -6424540398559729838L;
private final SqlSession sqlSession;
private final Class mapperInterface;
private final Map<Method, MapperMethod> methodCache;
public MapperProxy(SqlSession sqlSession, Class 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 (method.isDefault()) {
return invokeDefaultMethod(proxy, method, args);
}
} catch (Throwable t) {
throw ExceptionUtil.unwrapThrowable(t);
}
return mapperMethod.execute(sqlSession, args);
}
private MapperMethod cachedMapperMethod(Method method) {
return methodCache.computeIfAbsent(method, k -> new MapperMethod(mapperInterface, method, sqlSession.getConfiguration()));
}
}
执行Sql语句查询，由于我的返回结果是一个 User对象，所以会走到
result = sqlSession.selectOne(command.getName(), param);这一行，查询一条记录
实际走到 DefaultSqlSession.selectOne()
public class MapperMethod {
private final org.apache.ibatis.binding.MapperMethod.SqlCommand command;
private final org.apache.ibatis.binding.MapperMethod.MethodSignature method;
public MapperMethod(Class<?> mapperInterface, Method method, Configuration config) {
this.command = new org.apache.ibatis.binding.MapperMethod.SqlCommand(config, mapperInterface, method);
this.method = new org.apache.ibatis.binding.MapperMethod.MethodSignature(config, mapperInterface, method);
}
result = sqlSession.selectOne(command.getName(), param);
if (method.returnsOptional()
&& (result == null || !method.getReturnType().equals(result.getClass()))) {
result = Optional.ofNullable(result);
}
}
break;
case FLUSH: // 刷新
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;
}
}
查询多结果集
public class DefaultSqlSession implements SqlSession {
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();
}
}
}
码字不易，觉得有帮助的可以帮忙点个赞，让更多有需要的人看到
又是一年求职季，在这里，我为各位准备了一套Java程序员精选高频面试笔试真题，来帮助大家攻下BAT的offer，题目范围从初级的Java基础到高级的分布式架构等等一系列的面试题和答案，用于给大家作为参考
本文已被CODING开源项目：【一线大厂Java面试题解析+核心总结学习笔记+最新讲解视频+实战项目源码】收录
需要这份系统化的资料的朋友，可以点击这里获取
dStatement(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();
}
}
}
码字不易，觉得有帮助的可以帮忙点个赞，让更多有需要的人看到
又是一年求职季，在这里，我为各位准备了一套Java程序员精选高频面试笔试真题，来帮助大家攻下BAT的offer，题目范围从初级的Java基础到高级的分布式架构等等一系列的面试题和答案，用于给大家作为参考
以下是部分内容截图
[外链图片转存中…(img-ODVSBlH2-1715002820323)]
本文已被CODING开源项目：【一线大厂Java面试题解析+核心总结学习笔记+最新讲解视频+实战项目源码】收录