从字节数组中读取图片 [英] Reading picture from byte array

问题描述

我正在编写一个Java小程序，需要读取ZIP文件中的一些XML和图像文件。 Zip文件将通过HTTP下载，applet是无符号的，因此我需要使用 java.util.zip.ZipInputStream 来操作数据。当我尝试读取Zip文件中的PNG文件时出现问题。

I'm writing a Java applet that need to read some XML and image files inside a ZIP file. The Zip file will be download through HTTP and the applet is unsigned, so I need to use java.util.zip.ZipInputStream to manipulated the data. There's a problem when I'm trying to read a PNG file inside the Zip file.

我处理Zip文件的步骤：

The steps I handle the Zip file:

1. 通过Http下载Zip

1. Download the Zip through Http

URL resourceURL = new URL(source);
HttpURLConnection httpConnection= (HttpURLConnection) resourceURL.openConnection();
httpConnection.connect();
InputStream resourceFileIn = httpConnection.getInputStream();

使用ZipInputStream保存下载的数据

Use ZipInputStream to hold the data downloaded

ZipInputStream resourceZipIn = new ZipInputStream(resourceFileIn);

遍历每个ZipEntry并提取相应的字节数组

Iterate through every ZipEntry and extract the corresponding byte array

ArrayList<ExtractedEntry> extractedList = new ArrayList<ExtractedEntry>();
ZipEntry currentEntry;
while ((currentEntry = resourceZipIn.getNextEntry()) != null) {
    byte[] byteHolder = new byte[(int) currentEntry.getSize()];
    resourceZipIn.read(byteHolder, 0, byteHolder.length);
    extractedList.add(new ExtractedEntry(currentEntry.getName(), byteHolder));
}

备注：提取的每个ZipEntry都由以下类保存

remarks: every ZipEntry extracted is hold by the following class

public class ExtractedEntry {
    private String name;
    private byte[] byteArray;

    public ExtractedEntry(String name, byte[] byteArray) {
        super();
        this.name = name;
        this.byteArray = byteArray;
    }

    public String getName() {
        return name;
    }

    public byte[] getByteArray() {
        return byteArray;
    }
}

找到我要读取的文件在提取的列表中

Find the file I want to read from in the extracted list

ExtractedEntry bgEntry = null;
for (int j = 0; j < extractedList.size() && bgEntry == null; j++) {
    if (extractedList.get(j).getName().equals("background.png")) {
        bgEntry = extractedList.get(j);
    }
}

根据需要执行特定操作

Perform specific action according to need

InputStream mapBgIn = new ByteArrayInputStream(bgEntry.getByteArray());
BufferedImage bgEntry = ImageIO.read(bgIn);

---

<我只列出了读取PNG文件的动作，因为这是我遇到问题的地方。当我尝试以上述方式读取图像时，我总是在第5步的最后一行收到以下错误。

---

I list out only the action of reading the PNG file as that is where I encounter the problem. When I try to read the image in the way mentioned above, I always receive the following error at the last line of step 5.

javax.imageio.IIOException: Error reading PNG image data at com.sun.imageio.plugins.png.PNGImageReader.readImage(Unknown Source)
    at com.sun.imageio.plugins.png.PNGImageReader.read(Unknown Source)
    at javax.imageio.ImageIO.read(Unknown Source)
    at javax.imageio.ImageIO.read(Unknown Source)
    at com.quadd.soft.game.wtd.lib.resource.ResourceManager.loadHttpZipRes(ResourceManager.java:685)
Caused by: javax.imageio.IIOException: Unknown row filter type (= 7)!
    at com.sun.imageio.plugins.png.PNGImageReader.decodePass(Unknown Source)
    at com.sun.imageio.plugins.png.PNGImageReader.decodeImage(Unknown Source)
    ... 29 more

---

但是，如果我读了图像从下面的步骤3开始，没有问题。

---

However, if I read the image in the following way starting from step 3, there's no problem.

ZipInputStream resourceZipIn = new ZipInputStream(resourceFileIn);
ZipEntry testEntry;
while ((testEntry = resourceZipIn.getNextEntry()) != null) {
    if (testEntry.getName().equals("background.png")) {
        BufferedImage bgEntry = ImageIO.read(resourceZipIn);
    }
}

---

因此，我猜我的代码在从 java.util.zip.ZipInputStream 中提取字节时出现了一些问题，并将其放回以读取图像。但是我对操纵流很陌生，所以我无法弄清楚究竟是什么问题。我想问一下是否有人可以指出我在代码中犯了哪些错误导致错误。

---

Therefore, I guess that there's some problem with my code at extracting the bytes from java.util.zip.ZipInputStream and put it back for reading the image. But I'm quite new to manipulating stream so I just couldn't figure out what exactly is the problem. I would like to ask if anyone could point out what mistake I've made in the code which cause the error.

推荐答案

read 方法不保证它填充字节数组;它只读取一个小块并返回它读取的字节数。你需要一个循环，或者使用一个填充数组的辅助类。

The read method does not guarantee that it fills the byte array; it reads only a small block and returns the number of bytes that it read. You need a loop, or use a helper class that does fill the array.

例如

DataInputStream in = new DataInputStream(resourceZipIn);
in.readFully(byteHolder);
in.close();

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