Spring MVC 4 REST with protocol buffers not working - spring

Question

I am trying to use Spring MVC 4's Rest templates to support google protocol buffers as message format. I have am following this post on Spring framework blog
spring-mvc-google-protocol-buffers
I checked out the sourceCode trying to implement it in my environment.
I have two issues- I cannot get it to compile when I turn Java.version to 1.6 and i cannot get it to work as a webapp (don't know what
will be the context-root of the converted war file)
-Details-
I have a requirement to make this code work as a web-app and deploy on java6 container (weblogic 10.3.6 -servlet 2.5 compliant)
So i changed the java 8 features from the codebase to make it Java 6 compatible.
The only problem is when I change the pom.xml's following section
<properties>
<project.build.sourceEncoding>UTF-8</project.build.sourceEncoding>
<start-class>demo.DemoApplication</start-class>
<java.version>1.8</java.version>
</properties>
to change the java.version to 1.6 value, then try to do mvn clean install , the DemoApplicationTests class fails to compile with this error.
-google-protocol-buffers-master\src\test\java\demo\DemoApplicationTests.java:28: cannot find symbol
[ERROR] symbol : constructor RestTemplate(java.util.List<org.springframework.http.converter.protobuf.ProtobufHttpMessageConverter>) is not defined
[ERROR] location: class org.springframework.web.client.RestTemplate
The following link shows that Spring codebase normally doesn't have any Java 8 specific source code so not sure why this code only compiles in Java 8
https://spring.io/blog/2015/04/03/how-spring-achieves-compatibility-with-java-6-7-and-8
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The following link shows how to convert a spring boot application to a WAR app.
I did change the pom.xml packaging option to war.
The code gets build by mvn clean install without issues and the .war file gets generated.
But there's no web.xml - so i cannot tell what will be the context-root of the deployed web app.
I either way deployed the webapp on weblogic 10.3.6 ( which is java 6 compatible)
and it deployed fine.
But when I run the DemoApplicationTests (that I have changed to point straight to the URL
using this call (got the context-root from the weblogic console by clicking on the deployed web app)
ResponseEntity<CustomerProtos.Customer> customer = restTemplate.getForEntity(
"http://127.0.0.1:7001/demo-0.0.1-SNAPSHOT/customers/2", CustomerProtos.Customer.class);
I keep getting 404 not found error.
I have put up my changed code here.
https://github.com/robinbajaj123/spring-and-google-protocol-buffers
Your feedback will be appreciated.

Answer 1

You'd need to convert the Spring Boot app to also be a valid Servlet application. If you were using Servlet 3 or later and chose a .war-based deployment from start.spring.io you'd get a ServletIntializer which is a Java class that is the programmatic equivalent of web.xml. Since you're using 2.5, not 3.0, you need an explicit web.xml. You might check out this sample on how to get a Boot app hoisted up in a Servlet 2.5 environment, though using Servlet 2.5 is not recommended!. It's worth mentioning that Servlet 3.0 support was introduced in 2009..
Finally, this code uses Java 8 lambdas. You'll need to replace the lambdas with Java 6-equivalent code. One example I see is:
#Bean
CustomerRepository customerRepository() {
...
The last line in the #Bean definition returns a lambda: customers::get. Replace it with:
final Map<Integer, CustomerProtos.Customer> customers =
new ConcurrentHashMap<Integer, CustomerProtos.Customer>();
return new CustomerRepository() {
public CustomerProtos.Customer findById(int id) {
return customers.get( id) ;
}
};
Similarly, replace the forEach method in the List w/ an old-school for-in loop:
for (CustomerProtos.Customer c : Arrays.asList( ... )) {
customers.put(c.getId(), c);
}