400 Bad Request when uploading byte[] with Spring RestTemplate to SpringMVC rest endpoint

Question

I am trying to upload a byte[] that contains an image to my Spring rest service (running in Spring Boot, btw) as a MultipartFile with my client running Spring RestTemplate and am getting HttpClientErrorException: 400 Bad Request.

My endpoint:

@RequestMapping(value="/scale/{percent}", method= RequestMethod.POST)
public ResponseEntity scaleImage(@PathVariable("percent") float percent,
                                        @RequestParam("file") MultipartFile file) {

    try {
        if (!file.isEmpty()) {
            byte [] result = transformService.scaleImage(percent, file.getBytes());
            return getResponseEntityFromBytes(result);
        } else {
            return generateBadRequestError();
        }
    } catch (Exception e) {
        if (e instanceof InvalidOperationParameterException) {
            // TODO - populate message with bad parameters
            LOGGER.log(Level.FINE, "Invalid Parameters: ");
            return generateBadRequestError();
        } else {
            LOGGER.log(Level.SEVERE, "Exception caught: " + e.getMessage(), e);
            return generateServerError(e.getMessage());
        }
    }
}

My Spring RestTemplate client:

public void scaleImage(byte[] image, float percent) throws Exception {
    String url = "http://localhost:8080/scale/" + percent;
    this.testNumberThreads=10;
    this.testNumberThreads=10;

    MultiValueMap<String, Object> mvm = new LinkedMultiValueMap<>();
    mvm.add("file", image);
    TransformedResponse r = doPost(url, mvm);
}

private TransformedResponse doPost(String url, MultiValueMap<String, Object> mvm) {
    RestTemplate restTemplate = new RestTemplate();
    TransformedResponse xr = null;
    try {
        xr = restTemplate.postForObject(url, mvm, TransformedResponse.class);
    } catch (RestClientException e) {
        e.printStackTrace();
    }
    return xr;
}

...

public class TransformedResponse {
    byte[] image;

    public byte[] getImage() {
        return image;
    }

    public void setImage(byte[] image) {
        this.image = image;
    }
}

Here is the exception I'm seeing in the client (nothing hitting server yet):

org.springframework.web.client.HttpClientErrorException: 400 Bad Request
    at org.springframework.web.client.DefaultResponseErrorHandler.handleError(DefaultResponseErrorHandler.java:91)
    at org.springframework.web.client.RestTemplate.handleResponseError(RestTemplate.java:588)
    at org.springframework.web.client.RestTemplate.doExecute(RestTemplate.java:546)
    at org.springframework.web.client.RestTemplate.execute(RestTemplate.java:502)
    at org.springframework.web.client.RestTemplate.postForObject(RestTemplate.java:330)
    at com.me.image.xform.LoadTest.doPost(LoadTest.java:110)
    at com.me.image.xform.LoadTest.loadTestScalePercent(LoadTest.java:75)
    at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
    at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:57)
    at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
    at java.lang.reflect.Method.invoke(Method.java:606)
    at org.junit.runners.model.FrameworkMethod$1.runReflectiveCall(FrameworkMethod.java:47)
    at org.junit.internal.runners.model.ReflectiveCallable.run(ReflectiveCallable.java:12)
    at org.junit.runners.model.FrameworkMethod.invokeExplosively(FrameworkMethod.java:44)
    at org.junit.internal.runners.statements.InvokeMethod.evaluate(InvokeMethod.java:17)
    at org.springframework.test.context.junit4.statements.RunBeforeTestMethodCallbacks.evaluate(RunBeforeTestMethodCallbacks.java:74)
    at org.springframework.test.context.junit4.statements.RunAfterTestMethodCallbacks.evaluate(RunAfterTestMethodCallbacks.java:83)
    at org.springframework.test.context.junit4.statements.SpringRepeat.evaluate(SpringRepeat.java:72)
    at org.springframework.test.context.junit4.SpringJUnit4ClassRunner.runChild(SpringJUnit4ClassRunner.java:232)
    at org.springframework.test.context.junit4.SpringJUnit4ClassRunner.runChild(SpringJUnit4ClassRunner.java:89)
    at org.junit.runners.ParentRunner$3.run(ParentRunner.java:238)
    at org.junit.runners.ParentRunner$1.schedule(ParentRunner.java:63)
    at org.junit.runners.ParentRunner.runChildren(ParentRunner.java:236)
    at org.junit.runners.ParentRunner.access$000(ParentRunner.java:53)
    at org.junit.runners.ParentRunner$2.evaluate(ParentRunner.java:229)
    at org.springframework.test.context.junit4.statements.RunBeforeTestClassCallbacks.evaluate(RunBeforeTestClassCallbacks.java:61)
    at org.springframework.test.context.junit4.statements.RunAfterTestClassCallbacks.evaluate(RunAfterTestClassCallbacks.java:71)
    at org.junit.runners.ParentRunner.run(ParentRunner.java:309)
    at org.springframework.test.context.junit4.SpringJUnit4ClassRunner.run(SpringJUnit4ClassRunner.java:175)
    at org.junit.runner.JUnitCore.run(JUnitCore.java:160)
    at com.intellij.junit4.JUnit4IdeaTestRunner.startRunnerWithArgs(JUnit4IdeaTestRunner.java:74)
    at com.intellij.rt.execution.junit.JUnitStarter.prepareStreamsAndStart(JUnitStarter.java:211)
    at com.intellij.rt.execution.junit.JUnitStarter.main(JUnitStarter.java:67)

Why won't this request post correctly?

Answer 1

First of all, when using Spring, make sure that you have proper MultiPartFile resolver defined in your servlet context:

<bean id="multipartResolver"
      class="org.springframework.web.multipart.commons.CommonsMultipartResolver">
    <property name="maxUploadSize" value="52428800"/>
    <property name="maxInMemorySize" value="52428800"/>
</bean>

If you're using maven, this resolver is located in spring-web artifact:

<dependency>
    <groupId>org.springframework</groupId>
    <artifactId>spring-web</artifactId>
    <version>${your.spring.version}</version>
</dependency>

Then, create form and make sure you're using proper enctype:

<form method="post" action="upload.form" enctype="multipart/form-data">
    <input type="file" name="file"/>
    <input type="submit"/>
</form>

Finally, handle file upload in your controller

@RequestMapping(value="/path", method= RequestMethod.POST)
public StringscaleImage(@RequestParam("file") MultipartFile file) {
    //....
}

Remember that asynch file upload is supported only with HTML5, with others you'd need to use some workarounds (like flash or iframes).

If you're still facing 400 Error, add to your logging service this logger (or similar, depending on logging framework):

<appender name="console" class="org.apache.log4j.ConsoleAppender">
    <param name="Target" value="System.out"/>
    <param name="threshold" value="TRACE"/>
    <layout class="org.apache.log4j.PatternLayout">
        <param name="ConversionPattern" value="%d{HH:mm:ss,SSS} %-5p [%c] %m%n"/>
    </layout>
</appender>

<logger name="org.springframework.web.method.HandlerMethod">
    <level value="TRACE"/>
</logger>

<root>
    <priority value="info"/>
    <appender-ref ref="console"/>
</root>

It should output exception thrown during request handling

Answer 2

I found my problem. I needed to add an AbstractResource (in this case a ByteArrayResource) to my MultiValueMap instead of the raw byte array. Here's the code that fixed it:

public void scaleImage(byte[] image, float percent) throws Exception {
    String url = "http://localhost:8080/scale/" + percent;

    final byte[] rawBytes = image.clone();

    MultiValueMap<String, Object> mvm = new LinkedMultiValueMap<>();
    ByteArrayResource bar = new ByteArrayResource(rawBytes) {
        @Override
        public String getFilename() {
            return "Test-"+rawBytes.length + ".jpg";
        }
    };

    mvm.add("file", bar);
    TransformedResponse r = doPost(url, mvm);
}