Allow omit a 'method' attribute on SqlProvider annotation

Fixes gh-1279

Author: kazuki43zoo

src/main/java/org/apache/ibatis/annotations/DeleteProvider.java

@@ -1,5 +1,5 @@
 /**
- *    Copyright 2009-2016 the original author or authors.
+ *    Copyright 2009-2019 the original author or authors.
  *
  *    Licensed under the Apache License, Version 2.0 (the "License");
  *    you may not use this file except in compliance with the License.
@@ -30,5 +30,5 @@
 public @interface DeleteProvider {
   Class<?> type();
 
-  String method();
+  String method() default "";
 }

src/main/java/org/apache/ibatis/annotations/InsertProvider.java

@@ -1,5 +1,5 @@
 /**
- *    Copyright 2009-2016 the original author or authors.
+ *    Copyright 2009-2019 the original author or authors.
  *
  *    Licensed under the Apache License, Version 2.0 (the "License");
  *    you may not use this file except in compliance with the License.
@@ -30,5 +30,5 @@
 public @interface InsertProvider {
   Class<?> type();
 
-  String method();
+  String method() default "";
 }

src/main/java/org/apache/ibatis/annotations/SelectProvider.java

@@ -1,5 +1,5 @@
 /**
- *    Copyright 2009-2016 the original author or authors.
+ *    Copyright 2009-2019 the original author or authors.
  *
  *    Licensed under the Apache License, Version 2.0 (the "License");
  *    you may not use this file except in compliance with the License.
@@ -30,5 +30,5 @@
 public @interface SelectProvider {
   Class<?> type();
 
-  String method();
+  String method() default "";
 }

src/main/java/org/apache/ibatis/annotations/UpdateProvider.java

@@ -1,5 +1,5 @@
 /**
- *    Copyright 2009-2016 the original author or authors.
+ *    Copyright 2009-2019 the original author or authors.
  *
  *    Licensed under the Apache License, Version 2.0 (the "License");
  *    you may not use this file except in compliance with the License.
@@ -30,5 +30,5 @@
 public @interface UpdateProvider {
   Class<?> type();
 
-  String method();
+  String method() default "";
 }

src/main/java/org/apache/ibatis/builder/annotation/ProviderMethodResolver.java

@@ -0,0 +1,69 @@
+/**
+ *    Copyright 2009-2019 the original author or authors.
+ *
+ *    Licensed under the Apache License, Version 2.0 (the "License");
+ *    you may not use this file except in compliance with the License.
+ *    You may obtain a copy of the License at
+ *
+ *       http://www.apache.org/licenses/LICENSE-2.0
+ *
+ *    Unless required by applicable law or agreed to in writing, software
+ *    distributed under the License is distributed on an "AS IS" BASIS,
+ *    WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ *    See the License for the specific language governing permissions and
+ *    limitations under the License.
+ */
+
+package org.apache.ibatis.builder.annotation;
+
+import java.lang.reflect.Method;
+import java.util.Arrays;
+import java.util.Date;
+import java.util.List;
+import java.util.stream.Collectors;
+
+import org.apache.ibatis.builder.BuilderException;
+
+/**
+ * The interface that resolve an SQL provider method via an SQL provider class.
+ *
+ * <p> This interface need to implements at an SQL provider class and
+ * it need to define the default constructor for creating a new instance.
+ *
+ * @since 3.5.1
+ * @author Kazuki Shimizu
+ */
+public interface ProviderMethodResolver {
+
+  /**
+   * Resolve an SQL provider method.
+   *
+   * <p> The default implementation return a method that matches following conditions.
+   * <ul>
+   *   <li>Method name matches with mapper method</li>
+   *   <li>Return type matches the {@link CharSequence}({@link String}, {@link StringBuilder}, etc...)</li>
+   * </ul>
+   * If matched method is zero or multiple, it throws a {@link BuilderException}.
+   *
+   * @param context a context for SQL provider
+   * @return an SQL provider method
+   * @throws BuilderException Throws when cannot resolve a target method
+   */
+  default Method resolveMethod(ProviderContext context) {
+    List<Method> targetMethods = Arrays.stream(getClass().getMethods())
+        .filter(m -> m.getName().equals(context.getMapperMethod().getName()))
+        .filter(m -> CharSequence.class.isAssignableFrom(m.getReturnType()))
+        .collect(Collectors.toList());
+    if (targetMethods.size() == 1) {
+      return targetMethods.get(0);
+    }
+    if (targetMethods.isEmpty()) {
+      throw new BuilderException("Cannot resolve the provide method because '"
+          + context.getMapperMethod().getName() + "' not found in SqlProvider '" + getClass().getName() + "'.");
+    } else {
+      throw new BuilderException("Cannot resolve the provide method because '"
+          + context.getMapperMethod().getName() + "' is found multiple in SqlProvider '" + getClass().getName() + "'.");
+    }
+  }
+
+}

src/main/java/org/apache/ibatis/builder/annotation/ProviderSqlSource.java

@@ -62,16 +62,21 @@ public ProviderSqlSource(Configuration configuration, Object provider, Class<?>
       this.providerType = (Class<?>) provider.getClass().getMethod("type").invoke(provider);
       providerMethodName = (String) provider.getClass().getMethod("method").invoke(provider);
 
-      for (Method m : this.providerType.getMethods()) {
-        if (providerMethodName.equals(m.getName()) && CharSequence.class.isAssignableFrom(m.getReturnType())) {
-          if (providerMethod != null) {
-            throw new BuilderException("Error creating SqlSource for SqlProvider. Method '"
-                    + providerMethodName + "' is found multiple in SqlProvider '" + this.providerType.getName()
-                    + "'. Sql provider method can not overload.");
+      if (providerMethodName.length() == 0 && ProviderMethodResolver.class.isAssignableFrom(this.providerType)) {
+        this.providerMethod = ((ProviderMethodResolver) this.providerType.getDeclaredConstructor().newInstance())
+            .resolveMethod(new ProviderContext(mapperType, mapperMethod));
+      }
+      if (this.providerMethod == null) {
+        providerMethodName = providerMethodName.length() == 0 ? "provideSql" : providerMethodName;
+        for (Method m : this.providerType.getMethods()) {
+          if (providerMethodName.equals(m.getName()) && CharSequence.class.isAssignableFrom(m.getReturnType())) {
+            if (this.providerMethod != null) {
+              throw new BuilderException("Error creating SqlSource for SqlProvider. Method '"
+                  + providerMethodName + "' is found multiple in SqlProvider '" + this.providerType.getName()
+                  + "'. Sql provider method can not overload.");
+            }
+            this.providerMethod = m;
           }
-          this.providerMethod = m;
-          this.providerMethodArgumentNames = new ParamNameResolver(configuration, m).getNames();
-          this.providerMethodParameterTypes = m.getParameterTypes();
         }
       }
     } catch (BuilderException e) {
@@ -83,6 +88,8 @@ public ProviderSqlSource(Configuration configuration, Object provider, Class<?>
       throw new BuilderException("Error creating SqlSource for SqlProvider. Method '"
           + providerMethodName + "' not found in SqlProvider '" + this.providerType.getName() + "'.");
     }
+    this.providerMethodArgumentNames = new ParamNameResolver(configuration, this.providerMethod).getNames();
+    this.providerMethodParameterTypes = this.providerMethod.getParameterTypes();
     for (int i = 0; i < this.providerMethodParameterTypes.length; i++) {
       Class<?> parameterType = this.providerMethodParameterTypes[i];
       if (parameterType == ProviderContext.class) {

src/test/java/org/apache/ibatis/submitted/sqlprovider/CreateDB.sql

@@ -1,5 +1,5 @@
 --
---    Copyright 2009-2017 the original author or authors.
+--    Copyright 2009-2019 the original author or authors.
 --
 --    Licensed under the Apache License, Version 2.0 (the "License");
 --    you may not use this file except in compliance with the License.
@@ -15,15 +15,22 @@
 --
 
 drop table users if exists;
+drop table memos if exists;
 
 create table users (
   id int,
   name varchar(20),
   logical_delete boolean default false
 );
 
+create table memos (
+   id int,
+   memo varchar(1024),
+);
+
 insert into users (id, name) values(1, 'User1');
 insert into users (id, name) values(2, 'User2');
 insert into users (id, name) values(3, 'User3');
 insert into users (id, name, logical_delete) values(4, 'User4', true);
 
+insert into memos (id, memo) values(1, 'memo1');