Class cast exception in Groovy

问题

I want to upload an image using a groovy on grails. My gsp page is as follows (I am showing a simplified version of the original)

<g:form controller="post" action="save" enctype="multipart/form-data">        
      My picture  <input type="file" name="myPicture" />     
    <g:submitButton name="submit" value="Save"/>
</g:form>

My domain class is as follows:

class Post {    

byte[] myPicture

static mapping = {
    myPicture type:  "blob" 
}

I need this mapping otherwise MySql will create a smallblob which is to small to fit the images

static constraints = {
    myPicture(nullable:false)      
}

}

At the controller I have an action called save which is as follows:

def save = {                               
    def post = loadPost(params.id)

    post.properties = params

    if(post.save()) {
        print "hallo world"             
        redirect(action:'list', params:params)
    } else {
        render(view:'edit', model:[post:post])
    }
}

The exception is thrown when I try to save the image at the DB.

2009-04-27 18:16:07,319 [20806951@qtp0-0] ERROR errors.GrailsExceptionResolver  - java.lang.ClassCastException: [B cannot be cast to java.sql.Blob

org.codehaus.groovy.runtime.InvokerInvocationException: java.lang.ClassCastException: [B cannot be cast to java.sql.Blob

Any hint why is this?

BTW, I've seen in a tutorial that images were handled as strings but it didn't work as well.

回答1:

try this way:

  def save = {                               

    def post = loadPost(params.id)

    def f = request.getFile('myPicture')             

    post.myPicture = f.getBytes()
    post.pictureType = f.getContentType()                    


    if(post.save()) {

回答2:

I found a similar question on Nabble:

http://www.nabble.com/MySQL-and-Blobs-td16116885.html

Two possible solutions are suggested:

Change the constraints of the blob property to a large max-size, to stop it from using "TinyBlob".
Use the Hibernate Blob implementation instead of byte[] for the property's type declaration. This will require you stream data into the Blob, instead of direct assignment, but the post above gives code to do so.

回答3:

Can you try using Spring's MultipartFile within your loadPost() method?

Here's an example from the docs:

def upload = {
    def f = request.getFile('myFile')
    if(!f.empty) {
      f.transferTo( new File('/some/local/dir/myfile.txt') )
      response.sendError(200,'Done');
    }    
    else {
       flash.message = 'file cannot be empty'
       render(view:'uploadForm')
    }
}

I believe you can access f.bytes directly.

来源：https://stackoverflow.com/questions/794357/class-cast-exception-in-groovy

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grails

groovy

classcastexception