在上一篇文章Mybatis：Mapper接口编程原理分析（四）中，我们已经知道最终会进入 MapperMethod 类的 execute 方法进行正在的 CRUD 处理，现在才是真正的核心，前面都是为了现在做准备。因此，我们着重分析。
- MapperMethod
//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 List 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 if (SqlCommandType.FLUSH == 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() && !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 = Integer.valueOf(rowCount);
} else if (Long.class.equals(method.getReturnType()) || Long.TYPE.equals(method.getReturnType())) {
result = Long.valueOf(rowCount);
} 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.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 Object executeForMany(SqlSession sqlSession, Object[] args) {
List 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.selectList(command.getName(), param, rowBounds);
} else {
//没有分页则调用普通查询
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 Object convertToDeclaredCollection(Configuration config, List list) {
Object collection = config.getObjectFactory().create(method.getReturnType());
MetaObject metaObject = config.newMetaObject(collection);
metaObject.addAll(list);
return collection;
}
@SuppressWarnings("unchecked")
private E[] convertToArray(List list) {
E[] array = (E[]) Array.newInstance(method.getReturnType().getComponentType(), list.size());
array = list.toArray(array);
return array;
}
private Map executeForMap(SqlSession sqlSession, Object[] args) {
Map 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 extends HashMap {
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);
}
}
//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 SqlCommand(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
//
if (configuration.hasStatement(statementName)) {
ms = configuration.getMappedStatement(statementName);
} else if (!mapperInterface.equals(method.getDeclaringClass())) { // issue #35
String parentStatementName = method.getDeclaringClass().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 BindingException("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;
}
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 params;
//是否存在命名参数
private final boolean hasNamedParameters;
public MethodSignature(Configuration 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 = (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().intValue()];
} else {
final Map param = new ParamMap