Mapper代理

Posted 2020-12-03 贪吃的柳柳

getMapper-->mapperProxyFactory.newInstance(sqlSession)--> new MapperProxy<T>(sqlSession, mapperInterface, methodCache);至此生成代理类
后面用方法的时候如果有该方法直接从方法的缓存中拿，没有的话加入缓存，再执行方法。方法执行实际上都会走invoke这个方法，具体实现的是sqlsession的增删改查。
至于sql语句是SqlCommand根据mapper的类型.方法名从config这个类判断存不存在对应的xml ID，如果存在会把id传给sqlseesion。sqlsession里的MappedStatement ms = configuration.getMappedStatement(statement);这个找出对应的sql语句

总结：所有的代理类都是在启动的时候根据包扫描注册好了，方法不是，是用的时候才加到缓存，并且找xml的ID

 

package org.apache.ibatis.binding;
import org.apache.ibatis.builder.annotation.MapperAnnotationBuilder;
import org.apache.ibatis.io.ResolverUtil;
import org.apache.ibatis.session.Configuration;
import org.apache.ibatis.session.SqlSession;
import java.util.Collection;
import java.util.Collections;
import java.util.HashMap;
import java.util.Map;
import java.util.Set;
//这个类通过名字就可以看出 是用来注册Mapper接口与获取生成代理类实例的工具类
public class MapperRegistry {
//全局配置文件对象
private Configuration config;
//一个HashMap Key是mapper的类型对象, Value是MapperProxyFactory对象
//这个MapperProxyFactory是创建Mapper代理对象的工厂 我们一会再分析
private final Map<Class<?>, MapperProxyFactory<?>> knownMappers = new HashMap<Class<?>, MapperProxyFactory<?>>();
public MapperRegistry(Configuration config) {
this.config = config;
}
//获取生成的代理对象
@SuppressWarnings("unchecked")
public <T> T getMapper(Class<T> type, SqlSession sqlSession) {
//通过Mapper的接口类型 去Map当中查找 如果为空就抛异常
final MapperProxyFactory<T> mapperProxyFactory = (MapperProxyFactory<T>) knownMappers.get(type);
if (mapperProxyFactory == null)
throw new BindingException("Type " + type + " is not known to the MapperRegistry.");
try {
//否则创建一个当前接口的代理对象 并且传入sqlSession
return mapperProxyFactory.newInstance(sqlSession);
} catch (Exception e) {
throw new BindingException("Error getting mapper instance. Cause: " + e, e);
}
}

public <T> boolean hasMapper(Class<T> type) {
return knownMappers.containsKey(type);
}
//注册Mapper接口
public <T> void addMapper(Class<T> type) {
if (type.isInterface()) {
if (hasMapper(type)) {
throw new BindingException("Type " + type + " is already known to the MapperRegistry.");
}
boolean loadCompleted = false;
try {
knownMappers.put(type, new MapperProxyFactory<T>(type));
// It‘s important that the type is added before the parser is run
// otherwise the binding may automatically be attempted by the
// mapper parser. If the type is already known, it won‘t try.
MapperAnnotationBuilder parser = new MapperAnnotationBuilder(config, type);
parser.parse();
loadCompleted = true;
} finally {
if (!loadCompleted) {
knownMappers.remove(type);
}
}
}
}
public Collection<Class<?>> getMappers() {
return Collections.unmodifiableCollection(knownMappers.keySet());
}
ResolverUtil<Class<?>> resolverUtil = new ResolverUtil<Class<?>>();
resolverUtil.find(new ResolverUtil.IsA(superType), packageName);
Set<Class<? extends Class<?>>> mapperSet = resolverUtil.getClasses();
for (Class<?> mapperClass : mapperSet) {
addMapper(mapperClass);
}
}
//通过包名扫描下面所有接口
public void addMappers(String packageName) {
addMappers(packageName, Object.class);
}

}

package org.apache.ibatis.binding;
import java.lang.reflect.Method;
import java.lang.reflect.Proxy;
import java.util.Map;
import java.util.concurrent.ConcurrentHashMap;
import org.apache.ibatis.session.SqlSession;
//这个类负责创建具体Mapper接口代理对象的工厂类
public class MapperProxyFactory<T> {
//具体Mapper接口的Class对象
private final Class<T> mapperInterface;
//该接口下面方法的缓存 key是方法对象 value是对接口中方法对象的封装
private Map<Method, MapperMethod> methodCache = new ConcurrentHashMap<Method, MapperMethod>();
//构造参数没啥好说的
public MapperProxyFactory(Class<T> mapperInterface) {
this.mapperInterface = mapperInterface;
}
public Class<T> getMapperInterface() {
return mapperInterface;
}
public Map<Method, MapperMethod> getMethodCache() {
return methodCache;
}
@SuppressWarnings("unchecked")
protected T newInstance(MapperProxy<T> mapperProxy) {
//创建了一个代理类并返回
//关于Proxy的API 可以查看java官方的API
return (T) Proxy.newProxyInstance(mapperInterface.getClassLoader(), new Class[] { mapperInterface }, mapperProxy);
}
//在这里传入sqlSession 创建一个Mapper接口的代理类
public T newInstance(SqlSession sqlSession) {
//在这里创建了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, mapperInterface, methodCache);
//调用上面的方法 返回一个接口的代理类
return newInstance(mapperProxy);
}
}

package org.apache.ibatis.binding;
import java.io.Serializable;
import java.lang.reflect.InvocationHandler;
import java.lang.reflect.Method;
import java.util.Map;
import org.apache.ibatis.session.SqlSession;
//实现了JDK动态代理的接口 InvocationHandler
//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 有MapperProxyFactory传递过来的。
private final Map<Method, MapperMethod> methodCache;
//构造参数
public MapperProxy(SqlSession sqlSession, Class<T> mapperInterface, Map<Method, MapperMethod> methodCache) {
this.sqlSession = sqlSession;
this.mapperInterface = mapperInterface;
this.methodCache = methodCache;
}
//接口代理对象所有的方法调用 都会调用该方法
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())) {
return method.invoke(this, args);
}
//这里进行缓存
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(method);
if (mapperMethod == null) {
mapperMethod = new MapperMethod(mapperInterface, method, sqlSession.getConfiguration());
methodCache.put(method, mapperMethod);
}
return mapperMethod;
}
}

package org.apache.ibatis.binding;
import org.apache.ibatis.annotations.MapKey;
import org.apache.ibatis.annotations.Param;
import org.apache.ibatis.mapping.MappedStatement;
import org.apache.ibatis.mapping.SqlCommandType;
import org.apache.ibatis.reflection.MetaObject;
import org.apache.ibatis.session.Configuration;
import org.apache.ibatis.session.ResultHandler;
import org.apache.ibatis.session.RowBounds;
import org.apache.ibatis.session.SqlSession;
import java.lang.reflect.Array;
import java.lang.reflect.Method;
import java.util.*;
//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 update 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) {
this.command = new SqlCommand(config, mapperInterface, method);
this.method = new MethodSignature(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(sqlSession.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()) {
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 parameter, 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 = 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 {
//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() && !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 (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));
}
}
//返回多行结果 调用sqlSession.selectList方法
private <E> Object executeForMany(SqlSession sqlSession, Object[] 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 = sqlSession.<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(), 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;
}
@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, 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.<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 BindingException("Parameter ‘" + key + "‘ not found. Available parameters are " + keySet());
}
return super.get(key);
}
}


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 SqlCommand(Configuration configuration, Class<?> mapperInterface, Method method) throws BindingException {
//拿到全名 比如 org.mybatis.example.BlogMapper.selectBlog
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" resultType="Blog">
//select * from Blog where id = #{id}
//</select>
if (configuration.hasStatement(statementName)) {
ms = configuration.getMappedStatement(statementName);
} else if (!mapperInterface.equals(method.getDeclaringClass().getName())) { // 这里是一个BUG
String parentStatementName = method.getDeclaringClass().getName() + "." + method.getName();
if (configuration.hasStatement(parentStatementName)) {
ms = configuration.getMappedStatement(parentStatementName);
}
}
//为空抛出异常
if (ms == null) {
throw new BindingException("Invalid bound statement (not found): " + statementName);
}
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;
}
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;
//mapKey
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;
//在这里对上面的属性进行初始化 就不一一详细说明了 具体实现细节可以看下面的代码。
public MethodSignature(Configuration configuration, Method method) throws BindingException {
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 = (this.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.hasNamedParameters));
}
public Object convertArgsToSqlCommandParam(Object[] args) {
final int paramCount = params.size();
if (args == null || paramCount == 0) {
return null;
} else if (!hasNamedParameters && paramCount == 1) {
return args[params.keySet().iterator().next()];
} else {
final Map<String, Object> param = new ParamMap<Object>();
int i = 0;
for (Map.Entry<Integer, String> entry : params.entrySet()) {
param.put(entry.getValue(), args[entry.getKey()]);
// issue #71, add param names as param1, param2...but ensure backward compatibility
final String genericParamName = "param" + String.valueOf(i + 1);
if (!param.containsKey(genericParamName)) {
param.put(genericParamName, args[entry.getKey()]);
}
i++;
}
return param;
}
}
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;
}
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;
}
private SortedMap<Integer, String> getParams(Method method, boolean hasNamedParameters) {
final SortedMap<Integer, String> params = new TreeMap<Integer, String>();
final Class<?>[] argTypes = method.getParameterTypes();
for (int i = 0; i < argTypes.length; i++) {
if (!RowBounds.class.isAssignableFrom(argTypes[i]) && !ResultHandler.class.isAssignableFrom(argTypes[i])) {
String paramName = String.valueOf(params.size());
if (hasNamedParameters) {
paramName = getParamNameFromAnnotation(method, i, paramName);
}
params.put(i, paramName);
}
}
return params;
}
private String getParamNameFromAnnotation(Method method, int i, String paramName) {
final Object[] paramAnnos = method.getParameterAnnotations()[i];
for (Object paramAnno : paramAnnos) {
if (paramAnno instanceof Param) {
paramName = ((Param) paramAnno).value();
}
}
return paramName;
}
private boolean hasNamedParams(Method method) {
boolean hasNamedParams = false;
final Object[][] paramAnnos = method.getParameterAnnotations();
for (Object[] paramAnno : paramAnnos) {
for (Object aParamAnno : paramAnno) {
if (aParamAnno instanceof Param) {
hasNamedParams = true;
break;
}
}
}
return hasNamedParams;
}
}
}