Custom HttpMessageConverter with @ResponseBody to do Json things
Solution 1:
Well... it was so hard to find the answer and I had to follow so many clues to incomplete information that I think it will be good to post the complete answer here. So it will be easier for the next one searching for this.
First I had to implement the custom HttpMessageConverter:
package net.iogui.web.spring.converter;
import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStream;
import java.io.InputStreamReader;
import java.io.Reader;
import java.io.StringWriter;
import java.io.Writer;
import java.nio.charset.Charset;
import org.springframework.http.HttpInputMessage;
import org.springframework.http.HttpOutputMessage;
import org.springframework.http.MediaType;
import org.springframework.http.converter.AbstractHttpMessageConverter;
import org.springframework.http.converter.HttpMessageNotReadableException;
import org.springframework.http.converter.HttpMessageNotWritableException;
import com.google.gson.Gson;
import com.google.gson.JsonSyntaxException;
public class GsonHttpMessageConverter extends AbstractHttpMessageConverter<Object> {
private Gson gson = new Gson();
public static final Charset DEFAULT_CHARSET = Charset.forName("UTF-8");
public GsonHttpMessageConverter(){
super(new MediaType("application", "json", DEFAULT_CHARSET));
}
@Override
protected Object readInternal(Class<? extends Object> clazz,
HttpInputMessage inputMessage) throws IOException, HttpMessageNotReadableException {
try{
return gson.fromJson(convertStreamToString(inputMessage.getBody()), clazz);
}catch(JsonSyntaxException e){
throw new HttpMessageNotReadableException("Could not read JSON: " + e.getMessage(), e);
}
}
@Override
protected boolean supports(Class<?> clazz) {
return true;
}
@Override
protected void writeInternal(Object t,
HttpOutputMessage outputMessage) throws IOException, HttpMessageNotWritableException {
//TODO: adapt this to be able to receive a list of json objects too
String json = gson.toJson(t);
outputMessage.getBody().write(json.getBytes());
}
//TODO: move this to a more appropriated utils class
public String convertStreamToString(InputStream is) throws IOException {
/*
* To convert the InputStream to String we use the Reader.read(char[]
* buffer) method. We iterate until the Reader return -1 which means
* there's no more data to read. We use the StringWriter class to
* produce the string.
*/
if (is != null) {
Writer writer = new StringWriter();
char[] buffer = new char[1024];
try {
Reader reader = new BufferedReader(new InputStreamReader(is, "UTF-8"));
int n;
while ((n = reader.read(buffer)) != -1) {
writer.write(buffer, 0, n);
}
} finally {
is.close();
}
return writer.toString();
} else {
return "";
}
}
}
Then I had to strip off the annnotaion-driven tag and configure all by my own hands on the spring-mvc configuration file:
<?xml version="1.0" encoding="UTF-8"?>
<beans xmlns="http://www.springframework.org/schema/beans"
xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xmlns:context="http://www.springframework.org/schema/context"
xmlns:mvc="http://www.springframework.org/schema/mvc"
xsi:schemaLocation="http://www.springframework.org/schema/mvc http://www.springframework.org/schema/mvc/spring-mvc-3.0.xsd
http://www.springframework.org/schema/beans http://www.springframework.org/schema/beans/spring-beans-3.0.xsd
http://www.springframework.org/schema/context http://www.springframework.org/schema/context/spring-context-3.0.xsd">
<!-- Configures the @Controller programming model -->
<!-- To use just with a JSR-303 provider in the classpath
<bean id="validator" class="org.springframework.validation.beanvalidation.LocalValidatorFactoryBean" />
-->
<bean id="conversionService" class="org.springframework.format.support.FormattingConversionServiceFactoryBean" />
<bean class="org.springframework.web.servlet.mvc.annotation.AnnotationMethodHandlerAdapter">
<property name="webBindingInitializer">
<bean class="net.iogui.web.spring.util.CommonWebBindingInitializer" />
</property>
<property name="messageConverters">
<list>
<bean class="org.springframework.http.converter.ByteArrayHttpMessageConverter" />
<bean class="org.springframework.http.converter.StringHttpMessageConverter" />
<bean class="org.springframework.http.converter.ResourceHttpMessageConverter" />
<bean class="net.iogui.web.spring.converter.GsonHttpMessageConverter" />
<bean class="org.springframework.http.converter.xml.SourceHttpMessageConverter" />
<bean class="org.springframework.http.converter.xml.XmlAwareFormHttpMessageConverter" />
<!-- bean class="org.springframework.http.converter.xml.Jaxb2RootElementHttpMessageConverter" /-->
</list>
</property>
</bean>
<bean id="handlerMapping" class="org.springframework.web.servlet.mvc.annotation.DefaultAnnotationHandlerMapping" />
<context:component-scan base-package="net.iogui.teste.web.controller"/>
<!-- Forwards requests to the "/" resource to the "login" view -->
<mvc:view-controller path="/" view-name="home"/>
<!-- Handles HTTP GET requests for /resources/** by efficiently serving up static resources in the ${webappRoot}/resources/ directory -->
<mvc:resources mapping="/resources/**" location="/resources/" />
<bean id="viewResolver" class="org.springframework.web.servlet.view.InternalResourceViewResolver">
<property name="viewClass" value="org.springframework.web.servlet.view.JstlView"/>
<property name="prefix" value="/WEB-INF/view/"/>
<property name="suffix" value=".jsp"/>
</bean>
</beans>
See that, to make the Formater and Validator to work, we have to build a custom webBindingInitializer too:
package net.iogui.web.spring.util;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.core.convert.ConversionService;
import org.springframework.validation.Validator;
import org.springframework.web.bind.WebDataBinder;
import org.springframework.web.bind.support.WebBindingInitializer;
import org.springframework.web.context.request.WebRequest;
public class CommonWebBindingInitializer implements WebBindingInitializer {
@Autowired(required=false)
private Validator validator;
@Autowired
private ConversionService conversionService;
@Override
public void initBinder(WebDataBinder binder, WebRequest request) {
binder.setValidator(validator);
binder.setConversionService(conversionService);
}
}
An Interesting thing to see is that In order to make the configuration work without the annotaion-driven tag, we have to manually configure a AnnotationMethodHandlerAdapter and a DefaultAnnotationHandlerMapping. And in order to make the AnnotationMethodHandlerAdapter capable of handling formatting and validation, we had to configure a validator, a conversionService and to build a custom webBindingInitializer.
I hope all this helps someone else besides me.
On my desperate search, this @Bozho post was extremely util. I am also grateful to @GaryF couse his answer took me to the @Bozho post. To you that are trying to do this in Spring 3.1, see @Robby Pond answer.. A lot easier, isn't it?
Solution 2:
You need to create a GsonMessageConverter that extends AbstractHttpMessageConverter and use the mvc-message-converters tag to register your message converter. That tag will let your converter take precedence over the Jackson one.
Solution 3:
If you want to add a message converter without messing with xml here is a simple example
@Autowired
private RequestMappingHandlerAdapter adapter;
@PostConstruct
public void initStuff() {
List<HttpMessageConverter<?>> messageConverters = adapter.getMessageConverters();
BufferedImageHttpMessageConverter imageConverter = new BufferedImageHttpMessageConverter();;
messageConverters.add(0,imageConverter);
}
Solution 4:
I had situation where usage of Jackson would require me to alter other group's (in the same company) code. Didn't like that. So I chose to use Gson and register TypeAdapters as needed.
Hooked up a converter and wrote a few integration tests using spring-test (used to be spring-mvc-test). No matter what variation I tried (using mvc:annotation-driven OR manual definition of the bean). None of them worked. Any combination of these always used the Jackson Converter which kept on failing.
Answer> Turns out that MockMvcBuilders' standaloneSetup method "hard" coded the message converters to default versions and ignored all my changes above. Here is what worked:
@Autowired
private RequestMappingHandlerAdapter adapter;
public void someOperation() {
StandaloneMockMvcBuilder smmb = MockMvcBuilders.standaloneSetup(controllerToTest);
List<HttpMessageConverter<?>> converters = adapter.getMessageConverters();
HttpMessageConverter<?> ary[] = new HttpMessageConverter[converters.size()];
smmb.setMessageConverters(conveters.toArray(ary));
mockMvc = smmb.build();
.
.
}
Hope this helps someone, in the end I used annotation-driven and re-purposing android's converter