执行多线程数据库应用程序时发生java.lang.NullPointerException

创建多线程应用程序，该应用程序创建多个线程并查询数据库的同一个表

给定格式为的输入xml文件：

<transliteration>
<element>
    <source>about us</source>
</element>
</transliteration>

在线

if(map.get(sourceString) == null || map.get(sourceString).equals("") || map.get(sourceString).equals(sourceString))

所以一个线程被终止，另一个线程被完全执行并生成输出文件。我不明白这个问题，谁能给我一些解决这个问题的建议呢

---

谢谢

我怀疑地图内容在评估线路时会发生变化

if(map.get(sourceString) == null || map.get(sourceString).equals("") || map.get(sourceString).equals(sourceString))

这样，null检查成功，但从映射中获得的新值可能为null。地图不同步

把这行改成

String sourceStringValue = map.get(sourceString);
if(sourceStringValue == null || sourceStringValue.equals("") || map.get(sourceString).equals(sourceString))

---

谢谢大家的努力

我尝试使用不同的方法解决这个问题，不使用静态共享映射，而是使用ExecutorService和Callable接口方法

这是我的密码

try
        {
            doc = loadXmlContentToMemory(this.inputString);
            expr = xPath.compile("/transliteration/element//source");
            result = expr.evaluate(doc, XPathConstants.NODESET);

        }catch(ParserConfigurationException ex)
        {
            System.out.println("loadXmlError: "+ex.toString());
        }
        catch(IOException ex)
        {
            System.out.println("loadXmlError: "+ex.toString());
        }
        catch(SAXException ex)
        {
            System.out.println("loadXmlError: "+ex.toString());
        }
        catch(XPathExpressionException ex)
        {
            System.out.println("loadXmlError: "+ex.toString());
        }

        NodeList nodes = (NodeList) result;
        String sourceString = "";

        if(nodes.getLength() >0)
        {
            Map<String,String> fileMap = new HashMap<String,String>(); 
            ExecutorService executor = Executors.newFixedThreadPool(NTHREADS);

            for(int index =0; index <nodes.getLength(); index++)
            {
                sourceString = nodes.item(index).getTextContent();
                Callable<Map<String,String>> worker = new MultipleDatabaseCallable(sourceString,language);
                Future<Map<String,String>> map = executor.submit(worker);

                try
                {
                    //System.out.println(""+Thread.currentThread().getName()+"SourceString:: "+sourceString+"Map: "+map.get().get(sourceString));
                      fileMap.putAll(map.get());
                }catch(InterruptedException ex)
                {
                    System.out.println("future read: "+ex.toString());
                }
                catch(ExecutionException ex)
                {
                    System.out.println("future read: "+ex.toString());
                }
            }

            executor.shutdown();
            // Wait until all threads are finish
            while (!executor.isTerminated()) {

            }
            ExecutorService tokenExecutor = Executors.newFixedThreadPool(NTHREADS);
            for(int i =0 ;i<nodes.getLength();i++)
            {
                sourceString = nodes.item(i).getTextContent();
                if(fileMap.get(sourceString) == null || fileMap.get(sourceString).equals("") || fileMap.get(sourceString).equals(sourceString))
                {
                    fileMap.remove(sourceString);
                    Callable<Map<String,String>> worker = new MultipleTokenCallable(sourceString,language);
                    Future<Map<String,String>> map = tokenExecutor.submit(worker);

                    try
                    {
                        fileMap.putAll(map.get());
                    }
                    catch(InterruptedException ex)
                    {
                        System.out.println("Tokenized put Interupted exception: "+ex.toString());
                    }
                    catch(ExecutionException ex)
                    {
                        System.out.println("Tokenized put Execution exception: "+ex.toString());
                        ex.printStackTrace(System.out);
                    }

                    Element targetElement = doc.createElement("target");
                    String targetString = "";

                    String[] tokens = sourceString.trim().split("\\s+");

                    for(int itr=0; itr < tokens.length; itr++)
                    {
                        targetString = targetString+" "+fileMap.get(tokens[itr]);
                    }
                    targetElement.setTextContent(targetString.trim());
                    nodes.item(i).getParentNode().appendChild(targetElement);
                    //System.out.println(""+Thread.currentThread().getName()+" Target:  "+targetString+" Source:  "+sourceString);
                }
                else
                {
                    Element abc = doc.createElement("target");
                    abc.setTextContent(fileMap.get(sourceString));
                    nodes.item(i).getParentNode().appendChild(abc);
                }
            }

            tokenExecutor.shutdown();
            // Wait until all threads are finish
            while (!tokenExecutor.isTerminated()) {

            }
            try
            {
                Transformer transformer = TransformerFactory.newInstance().newTransformer();
                StreamResult strResult = new StreamResult(new File(this.inputString+"_out.xml"));
                if(doc != null && strResult != null)
                {
                    DOMSource source = new  DOMSource(doc);
                    transformer.transform(source, strResult);
                }
            }
            catch(TransformerException ex)
            {
               System.out.println(""+ex);
            }
            catch(TransformerFactoryConfigurationError ex)
            {
               System.out.println(""+ex);
            }

        }

试试看
{
doc=loadXmlContentToMemory（this.inputString）；
expr=xPath.compile（“/translation/element//source”）；
结果=expr.evaluate（doc，XPathConstants.NODESET）；
}捕获（ParserConfiguration异常ex）
{
System.out.println（“loadXmlError:+ex.toString（））；
}
捕获（IOEX异常）
{
System.out.println（“loadXmlError:+ex.toString（））；
}
捕获（SAXEx异常）
{
System.out.println（“loadXmlError:+ex.toString（））；
}
catch（XPathExpressionException-ex）
{
System.out.println（“loadXmlError:+ex.toString（））；
}
节点列表节点=（节点列表）结果；
字符串sourceString=“”；
if（nodes.getLength（）>0）
{
Map fileMap=newhashmap（）；
ExecutorService executor=Executors.newFixedThreadPool（n线程）；
for（int index=0；当该线程正在运行时，我怀疑索引
map
为空。
map=OutputRecords.getRecords（）；
是否将其设置为空？OutputRecords.getRecords（）；返回静态映射变量，该变量在类加载时初始化，它可能为空，但我不知道何时可以为空。是否尝试将映射变量声明为volatile？如果它是共享静态映射，则不应从多个线程同时读写。@JB Nizet那么如何从threadI tr的run方法返回值我也这么做了，但这对我不起作用。不过，我通过删除共享映射方法，使用ExecutorService和Callable接口，并使用call（）方法返回每个线程的值，解决了这个问题。谢谢大家的努力
if(map.get(sourceString) == null || map.get(sourceString).equals("") || map.get(sourceString).equals(sourceString))

if(map.get(sourceString) == null || map.get(sourceString).equals("") || map.get(sourceString).equals(sourceString))

String sourceStringValue = map.get(sourceString);
if(sourceStringValue == null || sourceStringValue.equals("") || map.get(sourceString).equals(sourceString))

try
        {
            doc = loadXmlContentToMemory(this.inputString);
            expr = xPath.compile("/transliteration/element//source");
            result = expr.evaluate(doc, XPathConstants.NODESET);

        }catch(ParserConfigurationException ex)
        {
            System.out.println("loadXmlError: "+ex.toString());
        }
        catch(IOException ex)
        {
            System.out.println("loadXmlError: "+ex.toString());
        }
        catch(SAXException ex)
        {
            System.out.println("loadXmlError: "+ex.toString());
        }
        catch(XPathExpressionException ex)
        {
            System.out.println("loadXmlError: "+ex.toString());
        }

        NodeList nodes = (NodeList) result;
        String sourceString = "";

        if(nodes.getLength() >0)
        {
            Map<String,String> fileMap = new HashMap<String,String>(); 
            ExecutorService executor = Executors.newFixedThreadPool(NTHREADS);

            for(int index =0; index <nodes.getLength(); index++)
            {
                sourceString = nodes.item(index).getTextContent();
                Callable<Map<String,String>> worker = new MultipleDatabaseCallable(sourceString,language);
                Future<Map<String,String>> map = executor.submit(worker);

                try
                {
                    //System.out.println(""+Thread.currentThread().getName()+"SourceString:: "+sourceString+"Map: "+map.get().get(sourceString));
                      fileMap.putAll(map.get());
                }catch(InterruptedException ex)
                {
                    System.out.println("future read: "+ex.toString());
                }
                catch(ExecutionException ex)
                {
                    System.out.println("future read: "+ex.toString());
                }
            }

            executor.shutdown();
            // Wait until all threads are finish
            while (!executor.isTerminated()) {

            }
            ExecutorService tokenExecutor = Executors.newFixedThreadPool(NTHREADS);
            for(int i =0 ;i<nodes.getLength();i++)
            {
                sourceString = nodes.item(i).getTextContent();
                if(fileMap.get(sourceString) == null || fileMap.get(sourceString).equals("") || fileMap.get(sourceString).equals(sourceString))
                {
                    fileMap.remove(sourceString);
                    Callable<Map<String,String>> worker = new MultipleTokenCallable(sourceString,language);
                    Future<Map<String,String>> map = tokenExecutor.submit(worker);

                    try
                    {
                        fileMap.putAll(map.get());
                    }
                    catch(InterruptedException ex)
                    {
                        System.out.println("Tokenized put Interupted exception: "+ex.toString());
                    }
                    catch(ExecutionException ex)
                    {
                        System.out.println("Tokenized put Execution exception: "+ex.toString());
                        ex.printStackTrace(System.out);
                    }

                    Element targetElement = doc.createElement("target");
                    String targetString = "";

                    String[] tokens = sourceString.trim().split("\\s+");

                    for(int itr=0; itr < tokens.length; itr++)
                    {
                        targetString = targetString+" "+fileMap.get(tokens[itr]);
                    }
                    targetElement.setTextContent(targetString.trim());
                    nodes.item(i).getParentNode().appendChild(targetElement);
                    //System.out.println(""+Thread.currentThread().getName()+" Target:  "+targetString+" Source:  "+sourceString);
                }
                else
                {
                    Element abc = doc.createElement("target");
                    abc.setTextContent(fileMap.get(sourceString));
                    nodes.item(i).getParentNode().appendChild(abc);
                }
            }

            tokenExecutor.shutdown();
            // Wait until all threads are finish
            while (!tokenExecutor.isTerminated()) {

            }
            try
            {
                Transformer transformer = TransformerFactory.newInstance().newTransformer();
                StreamResult strResult = new StreamResult(new File(this.inputString+"_out.xml"));
                if(doc != null && strResult != null)
                {
                    DOMSource source = new  DOMSource(doc);
                    transformer.transform(source, strResult);
                }
            }
            catch(TransformerException ex)
            {
               System.out.println(""+ex);
            }
            catch(TransformerFactoryConfigurationError ex)
            {
               System.out.println(""+ex);
            }

        }