org.apache.ibatis.binding.BindingException: Parameter 'arg0' not found.
为此特意翻阅了mybatis的官方说明,找到下面的例子
@SelectProvider(type = UserSqlBuilder.class, method = "buildGetUsersByName")
List getUsersByName(
@Param("name") String name, @Param("orderByColumn") String orderByColumn);
class UserSqlBuilder {
// If not use @Param, you should be define same arguments with mapper method
public static String buildGetUsersByName(
final String name, final String orderByColumn) {
return new SQL(){{
SELECT("*");
FROM("users");
WHERE("name like #{name} || '%'");
ORDER_BY(orderByColumn);
}}.toString();
}
// If use @Param, you can define only arguments to be used
public static String buildGetUsersByName(@Param("orderByColumn") final String orderByColumn) {
return new SQL(){{
SELECT("*");
FROM("users");
WHERE("name like #{name} || '%'");
ORDER_BY(orderByColumn);
}}.toString();
}
}
经过测试,官方代码中编写的第一种写法(dao层的 buildGetUserByName 方法在每个参数前加上 @Param注解,内部类对应的 buildGetUserByName 方法则只需要把参数名、数量与dao层上的@Param注解保持一致;),在3.4.2版本前是正常可用的,但到了3.4.2版本后就会报错。
org.apache.ibatis.binding.BindingException: Parameter 'arg0' not found.
在项目启动的过程中,mybatis会查找所有的@SelectProvider标签,根据对应的type属性找到内部类,构建ProviderSqlSource对象,其中关键点在 providerMethodArgumentNames (方法参数名数组)属性的赋值。
this.providerMethodArgumentNames = extractProviderMethodArgumentNames(m);
参数m代表当前的方法method,如官方例子中的 buildGetUserByName ;具体函数的实现:
private String[] extractProviderMethodArgumentNames(Method providerMethod) {
String[] argumentNames = new String[providerMethod.getParameterTypes().length];
for (int i = 0; i < argumentNames.length; i++) {
Param param = findParamAnnotation(providerMethod, i);
argumentNames[i] = param != null ? param.value() : "param" + (i + 1);
}
return argumentNames;
}
private Param findParamAnnotation(Method providerMethod, int parameterIndex) {
final Object[] annotations = providerMethod.getParameterAnnotations()[parameterIndex];
Param param = null;
for (Object annotation : annotations) {
if (annotation instanceof Param) {
param = Param.class.cast(annotation);
break;
}
}
return param;
}
根据代码可以知道是先查找@Param,有的情况下则把Param标签的值作为参数名,没有则用"param1"~"paramn"作为参数名。providerMethodArgumentNames的属性为"param1"~"paramn";
this.providerMethodArgumentNames = new ParamNameResolver(configuration, m).getNames();
参数configuration是mybatis的配置,参数m是method
public ParamNameResolver(Configuration config, Method method) {
final Class[] paramTypes = method.getParameterTypes();
final Annotation[][] paramAnnotations = method.getParameterAnnotations();
final SortedMap map = new TreeMap();
int paramCount = paramAnnotations.length;
// get names from @Param annotations
for (int paramIndex = 0; paramIndex < paramCount; paramIndex++) {
if (isSpecialParameter(paramTypes[paramIndex])) {
// skip special parameters
continue;
}
String name = null;
for (Annotation annotation : paramAnnotations[paramIndex]) {
if (annotation instanceof Param) {
hasParamAnnotation = true;
name = ((Param) annotation).value();
break;
}
}
if (name == null) {
// @Param was not specified.
if (config.isUseActualParamName()) {
name = getActualParamName(method, paramIndex);
}
if (name == null) {
// use the parameter index as the name ("0", "1", ...)
// gcode issue #71
name = String.valueOf(map.size());
}
}
map.put(paramIndex, name);
}
names = Collections.unmodifiableSortedMap(map);
}
private String getActualParamName(Method method, int paramIndex) {
if (Jdk.parameterExists) {
return ParamNameUtil.getParamNames(method).get(paramIndex);
}
return null;
}
由于没有使用@Param注解,代码会判断系统是否开启了 useActualParamName(使用java8的反射得到方法参数名),3.4.2版本后此属性默认为true,代码会执行ParamNameUtil.getParamNames()
public class ParamNameUtil {
private static List getParameterNames(Executable executable) {
final List names = new ArrayList();
final Parameter[] params = executable.getParameters();
for (Parameter param : params) {
names.add(param.getName());
}
return names;
}
}
因为代理的原因,这里获取到的名字就是"agr0"~"agrn",而不是实际代码编写的参数名;providerMethodArgumentNames的属性为"agr0"~"agrn";
假如把useActualParamName设置为false,获取到的参数名则为"0"~"n";providerMethodArgumentNames的属性为"0"~"n";
项目启动完毕后,当执行代码查询时,mybatis会执行下列代码
public MapperMethod(Class mapperInterface, Method method, Configuration config) {
this.command = new SqlCommand(config, mapperInterface, method);
this.method = new MethodSignature(config, mapperInterface, method);
}
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.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);
}
关键在于最后的
this.paramNameResolver = new ParamNameResolver(configuration, method);
这里的实现跟之前构建ProviderSqlSource时给providerMethodArgumentNames赋值是一样的,区别时这里获取的是mapper里面的方法和参数,由于mapper方法上有写@Param注解,这里就能正确获取到参数的名称,并赋值到paramNameResolver 中。
当执行execute()方法前,mybatis会把mapper方法的参数名数组和参数值转换扩充为map。
Object param = method.convertArgsToSqlCommandParam(args);
args就是参数值的数组
method.converArgsToSqlCommandParam()方法执行的是下面的逻辑
public Object convertArgsToSqlCommandParam(Object[] args) {
return paramNameResolver.getNamedParams(args);
}
/**
*
* A single non-special parameter is returned without a name.
* Multiple parameters are named using the naming rule.
* In addition to the default names, this method also adds the generic names (param1, param2,
* ...).
*
*/
public Object getNamedParams(Object[] args) {
final int paramCount = names.size();
if (args == null || paramCount == 0) {
return null;
} else if (!hasParamAnnotation && paramCount == 1) {
return args[names.firstKey()];
} else {
final Map param = new ParamMap
得到的map为["param1":"0","name":"123","param2":"","orderByColumn":""];
最终mybatis会执行下面的代码完成mapper中方法和SelectProvider类方法的参数对应
private Object[] extractProviderMethodArguments(Map params, String[] argumentNames) {
Object[] args = new Object[argumentNames.length];
for (int i = 0; i < args.length; i++) {
if (providerContextIndex != null && providerContextIndex == i) {
args[i] = providerContext;
} else {
args[i] = params.get(argumentNames[i]);
}
}
return args;
}
其中参数params就是我们上面获得到的mapper的map--["param1":"0","name":"123","param2":"","orderByColumn":""];参数argumentNames则为前面SelectProvider中的providerMethodArgumentNames,在3.4.2版本前为"param1"~"paramn",在3.4.2版本后为"arg0"~"argn"或"0"~"1";所以程序在3.4.2版本前可以正常跑,在在3.4.2版本后则报
org.apache.ibatis.binding.BindingException: Parameter 'arg0' not found.
org.apache.ibatis.binding.BindingException: Parameter '0' not found.
解决的办法很简单,在SelectProvider方法的参数名前对应加上与mapper方法一样的@Param注解。
文章参考了 等风de帆- 29、ParamNameResolver参数解析 和 彼岸的包子 的mybatis传多个参数(不使用@param注解情况下),3.4.2版本之后使用#{0}-#{n}引起的参数绑定异常,以及settings属性中useActualParamName的作用。