Java 将文件写入Blobstore AppEngine并服务于客户端

目标：客户端将字符串输入发送到服务器（应用程序引擎）。服务器修改输入，创建带有输出的文件，并将其提供给客户端。GWT项目

这是我的代码方案（服务器端和客户端），但我不知道如何将文件提供给客户端。每当我尝试在客户端输入任何BlobStore导入时，我都会在运行时（但不是在构建或编译时）出错

将文件写入Blobstore被标记为实验性的(http://code.google.com/appengine/docs/java/blobstore/overview.html#Writing_Files_to_the_Blobstore). 也许它还不起作用？你能帮我解决这个问题吗？即使不使用blob，只要实现了上述目标。多谢各位

ProjectServiceImpl.java

public class ProjectServiceImpl extends RemoteServiceServlet implements ProjectService 
{
    public String project(String input) throws IllegalArgumentException 
    {
        String output = doSomethingWith(input);
        FileService fileService = FileServiceFactory.getFileService();
        AppEngineFile file = fileService.createNewBlobFile("text/plain");
        boolean lock = true;
        FileWriteChannel writeChannel = fileService.openWriteChannel(file, lock);
        writeChannel.write(ByteBuffer.wrap("Hello world!".getBytes()));
        writeChannel.closeFinally();
        BlobKey blobKey = fileService.getBlobKey(file);
        BlobstoreService blobService = BlobstoreServiceFactory.getBlobstoreService();
    }
}

public interface ProjectService extends RemoteService {
    String project(String name) throws IllegalArgumentException;
}

public interface ProjectServiceAsync {
    void project(String input, AsyncCallback<String> callback)
            throws IllegalArgumentException;
}

ProjectService.java

public class ProjectServiceImpl extends RemoteServiceServlet implements ProjectService 
{
    public String project(String input) throws IllegalArgumentException 
    {
        String output = doSomethingWith(input);
        FileService fileService = FileServiceFactory.getFileService();
        AppEngineFile file = fileService.createNewBlobFile("text/plain");
        boolean lock = true;
        FileWriteChannel writeChannel = fileService.openWriteChannel(file, lock);
        writeChannel.write(ByteBuffer.wrap("Hello world!".getBytes()));
        writeChannel.closeFinally();
        BlobKey blobKey = fileService.getBlobKey(file);
        BlobstoreService blobService = BlobstoreServiceFactory.getBlobstoreService();
    }
}

public interface ProjectService extends RemoteService {
    String project(String name) throws IllegalArgumentException;
}

public interface ProjectServiceAsync {
    void project(String input, AsyncCallback<String> callback)
            throws IllegalArgumentException;
}

ProjectServiceAsync.java

public class ProjectServiceImpl extends RemoteServiceServlet implements ProjectService 
{
    public String project(String input) throws IllegalArgumentException 
    {
        String output = doSomethingWith(input);
        FileService fileService = FileServiceFactory.getFileService();
        AppEngineFile file = fileService.createNewBlobFile("text/plain");
        boolean lock = true;
        FileWriteChannel writeChannel = fileService.openWriteChannel(file, lock);
        writeChannel.write(ByteBuffer.wrap("Hello world!".getBytes()));
        writeChannel.closeFinally();
        BlobKey blobKey = fileService.getBlobKey(file);
        BlobstoreService blobService = BlobstoreServiceFactory.getBlobstoreService();
    }
}

public interface ProjectService extends RemoteService {
    String project(String name) throws IllegalArgumentException;
}

public interface ProjectServiceAsync {
    void project(String input, AsyncCallback<String> callback)
            throws IllegalArgumentException;
}

公共接口ProjectServiceAsync{ 无效项目（字符串输入，异步回调） 抛出IllegalArgumentException； } MyProject.java：客户端

[...]
projectService.project(originalString, new AsyncCallback<String>() {
    [...]
    public void onSuccess(final String result) 
    {
        BlobstoreService blobService = BlobstoreServiceFactory.getBlobstoreService();
    }
});

[…]
projectService.project（originalString，new AsyncCallback（）{
[...]
成功时公共无效（最终字符串结果）
{
BlobstoreService BlobsService=BlobstoreServiceFactory.getBlobstoreService（）；
}
});

您不能在客户端使用应用程序引擎API（包括blobstore API）。API仅适用于应用程序引擎应用程序，而不适用于用户Javascript。要提供一个blob，请按照说明操作。

谢谢，尼克！那么，只需在您提供的链接中添加service.java并将正确的blobKey传递给该类就足够了？不需要向MyProject.java添加任何Blob代码？我是否需要我的服务器端类来扩展HttpServlet而不是RemoteService，如链接中的示例所示？谢谢@user411103编写一个类似于演示中的servlet；它的工作原理取决于你想如何为你的斑点服务。您的servlet确实需要扩展HttpServlet。