Question

我正在尝试解析员工的XML文件，并且我想用XML中的数据创建所有员工的数组列表，但是当我运行程序并尝试解析XML文件时，给了我一个零点例外。这是我的XML文件：

<?xml version="1.0"?>
<employees>
    <employee>
        <name>Roberta Robertson</name>
        <manager>false</manager>
    </employee>
    <employee>
        <name>Taylor Meyers</name>
        <manager>true</manager>
    </employee>
    <employee>
        <name>John Mayer</name>
        <manager>true</manager>
    </employee>
</employees>

这是我解析XML文件的代码。当我按下GUI中的某个按钮时，我会调用该方法。

public class employeesParser {
private DocumentBuilder builder;
private XPath path;

private void employeesParser()
        throws ParserConfigurationException
{

    // create the documentbuiler and path
    DocumentBuilderFactory dbfactory 
                = DocumentBuilderFactory.newInstance();
    builder = dbfactory.newDocumentBuilder();
    XPathFactory xpfactory = XPathFactory.newInstance();
    path = xpfactory.newXPath();
}

// read the file
public ArrayList<Employee> loadEmployees(String fileName)
    throws SAXException, IOException, XPathExpressionException
{
    //parsing the file

    File f = new File(fileName);
    Document doc = builder.parse(f);

    //reading the file, extracting the employees, add employees to ArrayList
    int employeeCount = Integer.parseInt(path.evaluate(
        "count(/employees/employee)", doc));

    for (int i = 1; i <= employeeCount; i++)
    {
        String employeeName = path.evaluate(
        "/employees/employee[" + i + "]/name", doc);
        boolean managerStatus = Boolean.parseBoolean(path.evaluate(
                "employees/employee[" + i + "]/manager", doc));
        Employee employee = new Employee(employeeName, managerStatus);
        employeeList.add(employee);
    }

    return employeeList;

    }
}

这是我称之为方法的地方：

private void addEmployeeXMLActionPerformed(java.awt.event.ActionEvent evt) {                                               
    // TODO add your handling code here:
    try {
        employeesParser parser = new employeesParser();
        employeeList = parser.loadEmployees("employees.xml");
    }
    catch (SAXException|IOException|XPathExpressionException e) {
    }
}

根据异常消息，错误发生在以下代码行：

    Document doc = builder.parse(f);

在我的loadEmployees（）方法中找到。谁能告诉我我做错了什么？我之前使用的代码非常类似，并且它已经有效了。非常感谢！

Answer 1

在您的代码中，您没有为employeesParser定义构造函数。 DocumentBuilder和DocumentBuilderFactory的初始化位于名为“employeesParser”的私有方法中。您可以将此初始化代码移动到构造函数中，或者在loadEmployees（）方法的开头调用此employeesParser方法。

Java - 解析XML文件时出现空指针异常

1 个答案: