java - 使用java gwt生成内联图像

标签 java gwt base64 google-contacts-api inline-images

我正在尝试使用java编写内联图像。但图像不显示:

<img src="data:unknown;base64,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">

我觉得这是因为,我用base64对它进行了错误的编码,或者字符集是错误的。
因为当我返回我在网上找到的图片的以下代码时,一切正常(所以不是,我的浏览器不能显示内联图像):
<img src="data:unknown;base64,R0lGODlhDwAPAKECAAAAzMzM/////wAAACwAAAAADwAPAAACIISPeQHsrZ5ModrLlN48CXF8m2iQ3YmmKqVlRtW4MLwWACH+H09wdGltaXplZCBieSBVbGVhZCBTbWFydFNhdmVyIQAAOw==">

这是我如何生成图片代码。我打开一个url并尝试base64编码结果:
try {
    IoProvider.get().makeRequestAsText(url,
        new ResponseReceivedHandler<String>() {
          public void onResponseReceived(ResponseReceivedEvent<String> event) {
            final Response<String> response = event.getResponse();
            if (response.getStatusCode() == HTTP_OK){
            callback.onSuccess("data:unknown;base64,"
                + Base64.encode(response.getText()));
            }
          }
        }, options);
} catch ...

这是我使用的base64编码器:http://snipt.net/tweakt/gwt-base64/
有什么想法,为什么生成的图像是无效的?
编辑:
根据你的回答,我重写了一点代码。下面是它现在的样子:
IoProvider.get().makeRequest(url,
  new ResponseReceivedHandler<Object>() {
    public void onResponseReceived(ResponseReceivedEvent<Object> event) {
      final Response<Object> response = event.getResponse();
        if (response.getStatusCode() == HTTP_OK) {

          // not working
          callback.onSuccess("data:image/jpeg;base64,"
              + Base64Utils.toBase64(response.getText().getBytes()));

          // working image
          // callback.onSuccess("data:unknown;base64,R0lGODlhDwAPAKECAAAAzMzM/////wAAACwAAAAADwAPAAACIISPeQHsrZ5ModrLlN48CXF8m2iQ3YmmKqVlRtW4MLwWACH+H09wdGltaXplZCBieSBVbGVhZCBTbWFydFNhdmVyIQAAOw==");
        }
      }
}, options);

编辑后的代码生成以下代码:
<img src="data:image/jpeg;base64,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">

我还尝试转换字符集:
try {
  callback.onSuccess("data:image/jpeg;base64,"
    + Base64Utils.toBase64(response.getText().getBytes("ISO-8859-1")));
} catch (UnsupportedEncodingException e) { }

它产生了代码:
<img src="data:image/jpeg;base64,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">

如何将响应传递给base64编码器,而不将其转换为字符串?
response.getData()是一个对象,我希望它是byte[]。

最佳答案

Jochen
我用不同的Base64编码库做了大量测试:
(gwt-base64)http://snipt.net/tweakt/gwt-base64/
(谷歌)http://code.google.com/p/google-web-toolkit/source/browse/trunk/user/src/com/google/gwt/user/server/Base64Utils.java?r=5962
(阿帕奇)http://commons.apache.org/codec/
测试浏览器:Chrome 14.0.797.0
dev-m,火狐5
测试图像:jpeg、gif、png
测试代码:

public static void main(String [] args) throws IOException {
    File file = new File("./resources/so.png");
    BufferedInputStream bufRead =  new BufferedInputStream(new FileInputStream(file));
    ByteBuffer buffer = ByteBuffer.allocate(30*1024) ; // x kb
    byte[] c = new byte[1];     
    while ((bufRead.read(c))>0) { //1 byte/time to avoid buffer arithmetics 
        buffer.put(c);
    }
    byte[] data = new byte[buffer.position()];
    buffer.flip();
    buffer.get(data);
    String dataAsSt = new String(data); // transform the data to a string -- encoding error-prone
    //gwt-base64
    //String gwtBase64 = GwtBase64.encode(dataAsSt);  //doesn't work

    //google base64 impl
    String googleBase64 = Base64Utils.toBase64(data);

    //apache base64 codec
    Base64 base64codec = new Base64(-1);
    String apacheBase64 = base64codec.encodeToString(data);

    System.out.println("Google:"+googleBase64);
    System.out.println("Apache:"+apacheBase64);
    //System.out.println("GWTb64:"+gwtBase64);
}

结论:
(gwt-base64)根本不起作用。在我尝试的每个图像上都失败了:java.lang.StringIndexOutOfBoundsException: String index out of range。注意我注释掉了代码。
(google)浏览器无法理解它产生的base64编码。
(apache)使用这个构造函数:new base64(-1)=没有特征线,没有url安全。
信用点:如果将字符映射的最后2个字符:“$”、“u”修改为“+”、“/”,则可以使google实现正常工作。
我的主要结论是,您当前使用的base64库是错误的。
我建议在寻找替代实现时,尝试以二进制格式(byte[])保留图像和base64编码器之间的字节流。如果使用相同的编码/解码,则字符串可能工作,但如果在两个不同的位置(如客户机/服务器)进行编码和解码,则会有风险。
祝你好运!
PS:试试这个:-)
<img src="data:unknown;base64,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"/>

编辑:进一步研究
我花了太多的时间试图找到解决办法。gwt包装器不允许您获取原始数据,但可以使用jsni强制浏览器获取二进制数据:
native String getBinaryResource(String url) /*-{
    // ...implemented with JavaScript                 
    var req = new XMLHttpRequest();
    req.open("GET", url, false);  // The last parameter determines whether the request is asynchronous -> this case is sync.
    req.overrideMimeType('text/plain; charset=x-user-defined');
    req.send(null);
    if (req.status == 200) {                    
        return req.responseText;
    } else return null
}-*/;

这个JS Blog
帮了很多忙。
这个资源非常适合
了解
javascript幕布:
XMLHTTPRequestObject
我很想破解一个难题,但我已经应用了所有这些,但是base64编码不起作用。JS和Java包装器之间仍然存在编码问题,我无法将字符串解码回正确的字节[]。尝试了所有可能的编码组合。一种可能的方法是使用本地JavaScript库将Req.ServEXT置于Base64中,并将字符串返回给Java对应。
到目前为止你的原始问题。
现在,看看您问题背后的一些替代想法和要求:在我的研究中,我发现base64经常用于在服务器端内联图像,以避免在客户端获取图像时额外的http开销。它似乎也是css内联的流行替代品。
在这个问题的上下文中,代码正在客户端(浏览器)上工作,这些原因不适用。使用底层的XMLHTTPRequest获取图像二进制文件将创建从浏览器到服务器的额外http请求。考虑到在客户端上下文中,您显然拥有图像的url(被传递到IoProvider.get().makeRequest(*url*,...)中),如果图像对象:
(这可能不是最好的代码示例,但它为您提供了图片(对不起,双关语;-))
void setImage(String url) {
    final HTML imageHolder = new HTML();
    String imgTag = "<IMG src='"+url+"' />'";
    imageHolder.setHTML(imgTag);
    RootPanel.get("imageContainer").add(imageHolder); // imageContainer is a div
}

编辑:螺母开裂
最后找到了拼图中最后一个丢失的部分:如何从javascript字符串中正确解码二进制数据。注意一些注意事项:如果ie不支持本地xmlhttprequest上的overridemimetype方法,那么它们就不适用于ie。
native String getBinaryResource(String url) /*-{
    var req = new XMLHttpRequest();
    req.open("GET", url, false);  // The last parameter determines whether the request is asynchronous.
    req.overrideMimeType('text/plain; charset=x-user-defined');

    req.send(null);
    if (req.status == 200) {
        return req.responseText;
    } else return null
}-*/;

private void sendRequestBinary() {
    String url = URL.encode("/Computer_File_030.gif");
    String data = getBinaryResource(url);
    if (data != null) {
        // The secret sauce: Method to decode the binary data in the response string
        byte[] binData = new byte[data.length()];
        for (int i=0;i<data.length();i++) {
            binData[i] = (byte)(data.charAt(i) & 0xff);
        }
        final HTML imageHolder = new HTML();
        String base64=Base64Utils.toBase64(binData);

        String imgTag = "<IMG src='data:image/gif;base64,"+base64+"' />'";
        imageHolder.setHTML(imgTag);
            RootPanel.get("imageContainer").add(imageHolder);
            errorLabel.setText("Base64:");
    } else {
        errorLabel.setText("Another error :-(");
    }
}

本文翻译自 https://stackoverflow.com/questions/6409587/

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