Add FallbackStubFactory (Fixes #410)

Author: ST-DDT

build.gradle

@@ -9,7 +9,7 @@ buildscript {
         }
     }
     ext {
-        projectVersion = '2.10.0.RELEASE'
+        projectVersion = '2.10.1-SNAPSHOT'
 
         // https://github.com/grpc/grpc-java/releases
         grpcVersion = '1.31.1'

docs/en/versions.md

@@ -48,6 +48,7 @@ Current version.
 | Version | spring-boot | gRPC | Date |
 |:-------:|:-----------:|:----:| ---: |
 | 2.11.0* | 2.3.3 | 1.31.1 | TBA |
+| 2.10.1* | 2.3.3 | 1.31.1 | Aug, 2020 |
 | 2.10.0 | 2.3.3 | 1.31.1 | Aug, 2020 |
 | 2.9.0  | 2.3.1 | 1.30.0 | Jun, 2020 |
 | 2.8.0  | 2.2.7 | 1.29.0 | Jun, 2020 |

grpc-client-spring-boot-autoconfigure/src/main/java/net/devh/boot/grpc/client/inject/GrpcClientBeanPostProcessor.java

@@ -43,6 +43,7 @@
 import io.grpc.stub.AbstractStub;
 import net.devh.boot.grpc.client.channelfactory.GrpcChannelFactory;
 import net.devh.boot.grpc.client.nameresolver.NameResolverRegistration;
+import net.devh.boot.grpc.client.stubfactory.FallbackStubFactory;
 import net.devh.boot.grpc.client.stubfactory.StubFactory;
 
 /**
@@ -259,6 +260,7 @@ private AbstractStub<?> createStub(final Class<? extends AbstractStub<?>> stubCl
     private List<StubFactory> getStubFactories() {
         if (this.stubFactories == null) {
             this.stubFactories = new ArrayList<>(this.applicationContext.getBeansOfType(StubFactory.class).values());
+            this.stubFactories.add(new FallbackStubFactory());
         }
         return this.stubFactories;
     }

grpc-client-spring-boot-autoconfigure/src/main/java/net/devh/boot/grpc/client/stubfactory/FallbackStubFactory.java

@@ -0,0 +1,72 @@
+/*
+ * Copyright (c) 2016-2020 Michael Zhang <[email protected]>
+ *
+ * Permission is hereby granted, free of charge, to any person obtaining a copy of this software and associated
+ * documentation files (the "Software"), to deal in the Software without restriction, including without limitation the
+ * rights to use, copy, modify, merge, publish, distribute, sublicense, and/or sell copies of the Software, and to
+ * permit persons to whom the Software is furnished to do so, subject to the following conditions:
+ *
+ * The above copyright notice and this permission notice shall be included in all copies or substantial portions of the
+ * Software.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE
+ * WARRANTIES OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR
+ * COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR
+ * OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
+ */
+
+package net.devh.boot.grpc.client.stubfactory;
+
+import java.lang.reflect.Constructor;
+import java.lang.reflect.Method;
+import java.lang.reflect.Modifier;
+import java.lang.reflect.Parameter;
+
+import org.springframework.beans.BeanInstantiationException;
+
+import io.grpc.Channel;
+import io.grpc.stub.AbstractStub;
+
+/**
+ * The StubFactory which tries to find a suitable factory method or constructor as a last resort. This factory will
+ * always be the last one that is attempted.
+ *
+ * @author Daniel Theuke ([email protected])
+ */
+public final class FallbackStubFactory implements StubFactory {
+
+    @Override
+    public boolean isApplicable(final Class<? extends AbstractStub<?>> stubType) {
+        return true;
+    }
+
+    @Override
+    public AbstractStub<?> createStub(final Class<? extends AbstractStub<?>> stubType, final Channel channel) {
+        try {
+            // Search for public static *Grpc#new*Stub(Channel)
+            final Class<?> declaringClass = stubType.getDeclaringClass();
+            if (declaringClass != null) {
+                for (final Method method : declaringClass.getMethods()) {
+                    final String name = method.getName();
+                    final int modifiers = method.getModifiers();
+                    final Parameter[] parameters = method.getParameters();
+                    if (name.startsWith("new") && name.endsWith("Stub")
+                            && Modifier.isStatic(modifiers) && Modifier.isPublic(modifiers)
+                            && method.getReturnType().isAssignableFrom(stubType)
+                            && parameters.length == 1
+                            && Channel.class.equals(parameters[0].getType())) {
+                        return AbstractStub.class.cast(method.invoke(null, channel));
+                    }
+                }
+            }
+
+            // Search for a public constructor *Stub(Channel)
+            final Constructor<? extends AbstractStub<?>> constructor = stubType.getConstructor(Channel.class);
+            return constructor.newInstance(channel);
+
+        } catch (final Exception e) {
+            throw new BeanInstantiationException(stubType, "Failed to create gRPC client via FallbackStubFactory", e);
+        }
+    }
+
+}