Question

我尝试将JRVirtualPrintPage对象写入OutputStream，以便将其用于持久性文件。

但是当我从InputStream中读取时，我无法加载我在执行百分位数计算时定义的类

我的代码如下：

private void writePages() throws IOException, JRException {

 OutputStream pos = new OutputStream();
    ObjectOutputStream oos = new ObjectOutputStream(pos);

    List pages = print.getPages();

    numPages = pages == null ? 0 : pages.size();
    writeInt(numPages);

    pageFilePointers = new long[pages.size()];
    long pfpOffset = writeObject(pageFilePointers);


    for(int i = 0; i < numPages; i++) {
        if (interrupted)
            return;

        if (Thread.currentThread().isInterrupted()) {
            throw new JRException("Current thread interrupted.");
        }

        JRVirtualPrintPage vpage = (JRVirtualPrintPage)pages.get(i);

        oos.writeObject(vpage);


        for (JRPrintElement jrPrintElement : elements) {
            oos.writeObject(jrPrintElement);
        }

        pageFilePointers[i] = writeBytes(pos.getBytes());
    }

    long saveFP = file.getFilePointer();
    file.seek(pfpOffset);
    writeObject(pageFilePointers);
    file.seek(saveFP);
}

private void readPages() throws IOException, ClassNotFoundException {
    int numPages = readInt();
    pageFilePointers = (long[])readObject();

    AJPersistenceInputStream pis = new AJPersistenceInputStream();
    file.seek(pageFilePointers[0]);
    byte[] pageBytes = readBytes();
    pis.reset(pageBytes);
    ObjectInputStream ois = new ObjectInputStream(pis);

    JRVirtualPrintPage page = (JRVirtualPrintPage)ois.readObject();

    if (startIndex == endIndex) {
        for(int i=1; i<=startIndex; i++)
            page = getPrintPage(pis, ois, i);
        print.addPage(page);
    } else {
        endIndex = Math.min(endIndex, pageFilePointers.length-1);

        for(int i=0; i<=endIndex; i++) {
            if (i>0)    // else already read page index == 0
                page = getPrintPage(pis, ois, i);
            if (i >= startIndex)
                print.addPage(page);
        }
    }
}

我在下面收到了错误：

java.lang.ClassNotFoundException: com.alu.vital.vq.jasper.aggregation.AJPercentileAggregator
    at java.net.URLClassLoader$1.run(URLClassLoader.java:366)
    at java.net.URLClassLoader$1.run(URLClassLoader.java:355)
    at java.security.AccessController.doPrivileged(Native Method)
    at java.net.URLClassLoader.findClass(URLClassLoader.java:354)
    at java.lang.ClassLoader.loadClass(ClassLoader.java:424)
    at java.lang.ClassLoader.loadClass(ClassLoader.java:357)
    at java.lang.Class.forName0(Native Method)
    at java.lang.Class.forName(Class.java:270)
    at java.io.ObjectInputStream.resolveClass(ObjectInputStream.java:623)
    at java.io.ObjectInputStream.readNonProxyDesc(ObjectInputStream.java:1610)
    at java.io.ObjectInputStream.readClassDesc(ObjectInputStream.java:1515)
    at java.io.ObjectInputStream.readOrdinaryObject(ObjectInputStream.java:1769)
    at java.io.ObjectInputStream.readObject0(ObjectInputStream.java:1348)
    at java.io.ObjectInputStream.defaultReadFields(ObjectInputStream.java:1989)
    at java.io.ObjectInputStream.defaultReadObject(ObjectInputStream.java:499)
    at net.sf.jasperreports.engine.fill.JRTemplatePrintText.readObject(JRTemplatePrintText.java:91)

＆＃34; com.alu.vital.vq.jasper.aggregation.AJPercentileAggregator＆＃34; class是我定义为执行百分位计算的类。它是在构建报告时编译的。

为什么我使用JRVirtualPrintPage对象写入OutputStream，当从InputStream读取时，我还将对象转换为JRVirtualPrintPage类型，为什么会发生此异常？

请帮我解释一下这个细节。我该如何解决？我认为它适用于新的Virtualize机制，因为只有当我将 JasperReports 从3.7.4升级到5.0.1时才会出现此问题

Answer 1

答案在行

at java.io.ObjectInputStream.defaultReadFields（ObjectInputStream.java:1989）

at java.io.ObjectInputStream.defaultReadObject（ObjectInputStream.java:499）

从堆栈跟踪的底部。

您的JRVirtualPrintPage类似乎有一个AJPercentileAggregator类型的字段。因此，当您序列化JRVirtualPrintPage时，正在序列化其所有字段，因此AJPercentileAggregator也是如此。

你可以：

将自定义序列化程序写入JRVirtualPrintPage，跳过AJPercentileAggregator类型的字段。
将此字段标记为瞬态，从序列化中跳过

从InputStream读取readObject时找不到错误类

1 个答案: