Android：解析具有较大属性且内存使用率较低的JSON文件

概述我想知道是否存在使用Jackson解析JSON文件的“正确”方法,其中JSON文件包含一个巨大的属性,而无需将整个流加载到内存中.我需要保持较低的内存,因为它是Android应用程序.我不是在这里问如何Android:ParsinglargeJSONfile,而是一个属性确实很大而其他属性都没有关系.例如,假设

我想知道是否存在使用Jackson解析JSON文件的“正确”方法,其中JSON文件包含一个巨大的属性,而无需将整个流加载到内存中.我需要保持较低的内存,因为它是Android应用程序.我不是在这里问如何Android: Parsing large JSON file,而是一个属性确实很大而其他属性都没有关系.

例如,假设我有以下内容：

{    "filename": "afilename.jpg",    "data": "**Huge data here, about 20Mb base64 string**",    "mime": "mimeType",    "otherPropertIEs": "..."}

如果需要,可以将data属性提取到一个新文件中(通过outputstream或其他含义),但是我无法使用Jackson来实现.可以使用其他库,我只是以为杰克逊的流API可以使它成为理想的库.

谢谢

解决方法:

最终,我设法恢复了如此庞大的数据,其中,在Json文件上有一个输入流,我想从中解析数据,然后是要将数据写入其中的文件：

public boolean extrationContenudocument(fileinputStream in, fileOutputStream out, fileInfo info) throws JsonParseException, IOException {    SerializedString keyDocContent = new SerializedString("data");    boolean isDone = false;    JsonParser jp = this.JsonFactory.createJsonParser(in);    // Let's move our inputstream cursor until the 'data' property is found    while (!jp.nextFIEldname(keyDocContent)) {        Log.v("Traitement JsON", "Searching for 'data' property ...");    }    // Found it? Ok, move the inputstream cursor until the begining of it's    // content    JsonToken current = jp.nextToken();    // if the current token is not String value it means u dIDn't found the    // 'data' property or it's content is not a correct => stop    if (current == JsonToken.VALUE_STRING) {        Log.v("Traitement JsON", "Property 'data' found");        // Here it gets a little tricky cause if the file is not big enough        // all the content of the 'data' property Could be read directly        // insted of using this        if (info.getSize() > TAILLE_MIN_PETIT_FICHER) {            Log.v("Traitement JsON", "the content of 'data' is too big to be read directly -> using buffered reading");            // JsonParser uses a buffer to read, there is some data that            // Could have been read by it, i need to fetch it            ByteArrayOutputStream debutDocStream = new ByteArrayOutputStream();            int premIErePartIERead = jp.releaseBuffered(debutDocStream);            byte[] debutDoc = debutDocStream.toByteArray();            // Write the head of the content of the 'data' property, this is            // actually what as read from the inputstream by the JsonParser            // when dID jp.nextToken()            Log.v("Traitement JsON", "Write the head");            out.write(debutDoc);            // Now we need to write the rest until we find the tail of the            // content of the 'data' property            Log.v("Traitement JsON", "Write the mIDdle");            // So i prepare a buffer to continue reading the inputstream            byte[] buffer = new byte[TAILLE_BUFFER_GROS_FICHER];            // The escape char that determines where to stop reading will be "            byte endChar = (byte) '"';            // Fetch me some bytes from the inputstream            int bytesRead = in.read(buffer);            int bytesBeforeEndChar = 0;            int deuxIEmePartIERead = 0;            boolean isDocContentFin = false;            // Are we at the end of the 'data' property? Keep writing the            // content of the 'data' property if it's not the case            while ((bytesRead > 0) && !isDocContentFin) {                bytesBeforeEndChar = 0;                // Since am using a buffer the escape char Could be in the                // mIDdle of it, gotta look if it is                for (byte b : buffer) {                    if (b != endChar) {                        bytesBeforeEndChar++;                    } else {                        isDocContentFin = true;                        break;                    }                }                if (bytesRead > bytesBeforeEndChar) {                    Log.v("Traitement JsON", "Write the tail");                    out.write(buffer, 0, bytesBeforeEndChar);                    deuxIEmePartIERead += bytesBeforeEndChar;                } else {                    out.write(buffer, 0, bytesRead);                    deuxIEmePartIERead += bytesRead;                }                bytesRead = in.read(buffer);            }            Log.v("Traitement JsON", "Bytes read: " + (premIErePartIERead + deuxIEmePartIERead) + " (" + premIErePartIERead + " head,"                    + deuxIEmePartIERead + " tail)");            isDone = true;        } else {            Log.v("Traitement JsON", "file is small enough to be read directly");            String contenuFichIEr = jp.getText();            out.write(contenuFichIEr.getBytes());            isDone = true;        }    } else {        throw new JsonParseException("The property " + keyDocContent.getValue() + " Couldn't be found in the Json Stream.", null);    }    jp.close();    return isDone;}

它虽然不漂亮,但是却像魅力一样！ @staxman让我知道您的想法.

编辑：

现在这是已实现的功能,请参阅：https://github.com/FasterXML/jackson-core/issues/14
和JsonParser.readBinaryValue()

总结

以上是内存溢出为你收集整理的Android：解析具有较大属性且内存使用率较低的JSON文件全部内容，希望文章能够帮你解决Android：解析具有较大属性且内存使用率较低的JSON文件所遇到的程序开发问题。

如果觉得内存溢出网站内容还不错，欢迎将内存溢出网站推荐给程序员好友。