java.lang.IllegalArgumentException:要分析的InputStream为null

请帮助我知道我的代码有什么问题。操作系统：Windows7

代码1:

 DigestStudents ds = (DigestStudents) digester.parse(this.getClass()
                            .getClassLoader()
                            .getResourceAsStream("leo/test/digester/student/student.xml"));

true:isFile:isHidden:false    
java.lang.IllegalArgumentException: InputStream to parse is null
at org.apache.commons.digester3.Digester.parse(Digester.java:1621)
at leo.test.digester.student.DigestStudents.digest(DigestStudents.java:41)
at leo.test.digester.student.DigestStudents.main(DigestStudents.java:16)

 File f = new File ("D:/workspace/RD_Axway/src/leo/test/digester/student/student.xml");
 System.out.println(f.isFile()+":isFile:isHidden:"+f.isHidden());
 DigestStudents ds = (DigestStudents) digester.parse(f);

true:isFile:isHidden:false
log4j:WARN No appenders could be found for logger (org.apache.commons.digester3.Digester).
log4j:WARN Please initialize the log4j system properly.
java.lang.NullPointerException
    at org.apache.commons.digester3.Digester.getXMLReader(Digester.java:790)
    at org.apache.commons.digester3.Digester.parse(Digester.java:1588)
    at org.apache.commons.digester3.Digester.parse(Digester.java:1557)
    at leo.test.digester.student.DigestStudents.digest(DigestStudents.java:41)
    at leo.test.digester.student.DigestStudents.main(DigestStudents.java:16)

例外情况1:

 DigestStudents ds = (DigestStudents) digester.parse(this.getClass()
                            .getClassLoader()
                            .getResourceAsStream("leo/test/digester/student/student.xml"));

true:isFile:isHidden:false    
java.lang.IllegalArgumentException: InputStream to parse is null
at org.apache.commons.digester3.Digester.parse(Digester.java:1621)
at leo.test.digester.student.DigestStudents.digest(DigestStudents.java:41)
at leo.test.digester.student.DigestStudents.main(DigestStudents.java:16)

 File f = new File ("D:/workspace/RD_Axway/src/leo/test/digester/student/student.xml");
 System.out.println(f.isFile()+":isFile:isHidden:"+f.isHidden());
 DigestStudents ds = (DigestStudents) digester.parse(f);

true:isFile:isHidden:false
log4j:WARN No appenders could be found for logger (org.apache.commons.digester3.Digester).
log4j:WARN Please initialize the log4j system properly.
java.lang.NullPointerException
    at org.apache.commons.digester3.Digester.getXMLReader(Digester.java:790)
    at org.apache.commons.digester3.Digester.parse(Digester.java:1588)
    at org.apache.commons.digester3.Digester.parse(Digester.java:1557)
    at leo.test.digester.student.DigestStudents.digest(DigestStudents.java:41)
    at leo.test.digester.student.DigestStudents.main(DigestStudents.java:16)

代码2:

 DigestStudents ds = (DigestStudents) digester.parse(this.getClass()
                            .getClassLoader()
                            .getResourceAsStream("leo/test/digester/student/student.xml"));

true:isFile:isHidden:false    
java.lang.IllegalArgumentException: InputStream to parse is null
at org.apache.commons.digester3.Digester.parse(Digester.java:1621)
at leo.test.digester.student.DigestStudents.digest(DigestStudents.java:41)
at leo.test.digester.student.DigestStudents.main(DigestStudents.java:16)

 File f = new File ("D:/workspace/RD_Axway/src/leo/test/digester/student/student.xml");
 System.out.println(f.isFile()+":isFile:isHidden:"+f.isHidden());
 DigestStudents ds = (DigestStudents) digester.parse(f);

true:isFile:isHidden:false
log4j:WARN No appenders could be found for logger (org.apache.commons.digester3.Digester).
log4j:WARN Please initialize the log4j system properly.
java.lang.NullPointerException
    at org.apache.commons.digester3.Digester.getXMLReader(Digester.java:790)
    at org.apache.commons.digester3.Digester.parse(Digester.java:1588)
    at org.apache.commons.digester3.Digester.parse(Digester.java:1557)
    at leo.test.digester.student.DigestStudents.digest(DigestStudents.java:41)
    at leo.test.digester.student.DigestStudents.main(DigestStudents.java:16)

例外情况2:

 DigestStudents ds = (DigestStudents) digester.parse(this.getClass()
                            .getClassLoader()
                            .getResourceAsStream("leo/test/digester/student/student.xml"));

true:isFile:isHidden:false    
java.lang.IllegalArgumentException: InputStream to parse is null
at org.apache.commons.digester3.Digester.parse(Digester.java:1621)
at leo.test.digester.student.DigestStudents.digest(DigestStudents.java:41)
at leo.test.digester.student.DigestStudents.main(DigestStudents.java:16)

 File f = new File ("D:/workspace/RD_Axway/src/leo/test/digester/student/student.xml");
 System.out.println(f.isFile()+":isFile:isHidden:"+f.isHidden());
 DigestStudents ds = (DigestStudents) digester.parse(f);

true:isFile:isHidden:false
log4j:WARN No appenders could be found for logger (org.apache.commons.digester3.Digester).
log4j:WARN Please initialize the log4j system properly.
java.lang.NullPointerException
    at org.apache.commons.digester3.Digester.getXMLReader(Digester.java:790)
    at org.apache.commons.digester3.Digester.parse(Digester.java:1588)
    at org.apache.commons.digester3.Digester.parse(Digester.java:1557)
    at leo.test.digester.student.DigestStudents.digest(DigestStudents.java:41)
    at leo.test.digester.student.DigestStudents.main(DigestStudents.java:16)

Student.java

package leo.test.digester.student;

public class Student {
private String name;
private String course;

public Student() {
}

public String getName() {
    return name;
}

public void setName(String newName) {
    name = newName;
}

public String getCourse() {
    return course;
}

public void setCourse(String newCourse) {
    course = newCourse;
}
public String toString() {
    return("Name="+this.name + " & Course=" +  this.course);
}
}

package leo.test.digester.student;

import java.util.Vector;
import org.apache.commons.digester3.Digester;

public class DigestStudents {
    Vector students;

    public DigestStudents() {
        students= new Vector();
    }

    public static void main(String[] args) {
        DigestStudents digestStudents = new DigestStudents();
        digestStudents.digest();
    }

    private void digest() {
        try {
            Digester digester = new Digester();
            //Push the current object onto the stack
            digester.push(this);

            //Creates a new instance of the Student class
            digester.addObjectCreate( "students/student", Student.class );

            //Uses setName method of the Student instance
            //Uses tag name as the property name
            digester.addBeanPropertySetter( "students/student/name");

            //Uses setCourse method of the Student instance
            //Explicitly specify property name as 'course'
            digester.addBeanPropertySetter( "students/student/course", "course" );

            //Move to next student
            digester.addSetNext( "students/student", "addStudent" );

             File f = new File ("D:/workspace/RD_Axway/src/leo/test/digester/student/student.xml");
             System.out.println(f.isFile()+":isFile:isHidden:"+f.isHidden());


            DigestStudents ds = (DigestStudents) digester.parse(this.getClass()
                                .getClassLoader()
                                .getResourceAsStream("D:/workspace/RD_Axway/src/leo/test/digester/student/student.xml"));

            //Print the contents of the Vector
            System.out.println("Students Vector "+ds.students);
        } catch (Exception ex) {
            ex.printStackTrace();
        }
    }

    public void addStudent( Student stud ) {
        //Add a new Student instance to the Vector
        students.add( stud );
    }
}

student.xml

<?xml version="1.0" encoding="UTF-8"?>
<students>
        <student>
                <name>Java Boy</name>
                <course>JSP</course>
        </student>
        <student>
                <name>Java Girl</name>
                <course>EJB</course>
        </student>
</students>

---

我认为这句话有问题：

DigestStudents ds=（DigestStudents）digester.parse（this.getClass（）.getClassLoader（）.getResourceAsStream（“D:/workspace/RD_Axway/src/leo/test/digester/student/student.xml”）

找不到资源，因此返回null。
我认为这行有问题：

DigestStudents ds=（DigestStudents）digester.parse（this.getClass（）.getClassLoader（）.getResourceAsStream（“D:/workspace/RD_Axway/src/leo/test/digester/student/student.xml”）

找不到资源，因此返回null。
ClassLoader.getResourceAsStream在类路径中查找文件。
将getResourceAsStream更改为：

.getResourceAsStream("student.xml"));

确保指定了路径

D:/workspace/RD_Axway/src/leo/test/digester/student/

在类路径中，然后重新编译并再次运行它。
ClassLoader.getResourceAsStream在类路径中查找文件。
将getResourceAsStream更改为：

.getResourceAsStream("student.xml"));

确保指定了路径

D:/workspace/RD_Axway/src/leo/test/digester/student/

在类路径中，然后重新编译并再次运行它。
和
getResourceAsStream
都处理与类路径相关的URI

您需要修改路径，使其与

getResourceAsStream("/leo/test/digester/student/student.xml");

getResource
和
getresourceastream
都处理与类路径相关的URI

您需要修改路径，使其与

getResourceAsStream("/leo/test/digester/student/student.xml");

ClassLoader#getResourceAsStream（）
能够定位相对于类路径的“根””的文件。您需要替换此行：

 DigestStudents ds = (DigestStudents) digester.parse(this.getClass()
                       .getClassLoader()
                       .getResourceAsStream("D:/workspace/RD_Axway/src/leo/test/digester/student/student.xml"));

与

ClassLoader#getResourceAsStream（）
能够定位相对于类路径的“根””的文件。您需要替换此行：

 DigestStudents ds = (DigestStudents) digester.parse(this.getClass()
                       .getClassLoader()
                       .getResourceAsStream("D:/workspace/RD_Axway/src/leo/test/digester/student/student.xml"));

与

获取加载我们类的对象的整个想法是能够从当前的系统设置、当前的绝对路径中独立地获取资源。
您在
getResourceAsStream
中得到null，因为找不到文件。只需按照Kayaman的建议，将
student.xml的路径设置为相对路径，或绝对路径

this.getClass()
.getClassLoader()
.getResourceAsStream("path/to/file/student.xml")

您可以通过
classLoader.getResourceAsStream
以与加载当前类相同的路径搜索顺序获取文件。有关getResource，请参见javadoc：

java.lang.ClassLoader.getResource（字符串名称）

查找具有给定名称的资源。资源是一些数据
（图像、音频、文本等）可以通过类代码以某种方式访问
这与代码的位置无关

资源的名称是以“/”分隔的路径名，用于标识
资源

此方法将首先在父类装入器中搜索
资源；如果父级为null，则类装入器内置的路径为空
搜索到虚拟机。如果失败，这种方法将
调用findResource（字符串）以查找资源

由于这种通用性，代码更具可移植性，无论您是在Windows还是Linux上，甚至是在某些分布式系统上。关于加载类和可能的源的更多信息：
获取加载类的对象的整个想法是能够从当前的系统设置、从当前的绝对路径独立地获取资源。
您在
getResourceAsStream
中得到null，因为找不到文件。只需按照Kayaman的建议，将
student.xml的路径设置为相对路径，或绝对路径

this.getClass()
.getClassLoader()
.getResourceAsStream("path/to/file/student.xml")

您可以通过
classLoader.getResourceAsStream
以与加载当前类相同的路径搜索顺序获取文件。有关getResource，请参见javadoc：

java.lang.ClassLoader.getResource（字符串名称）

查找具有给定名称的资源。资源是一些数据
（图像、音频、文本等）可以通过类代码以某种方式访问
这与代码的位置无关

资源的名称是以“/”分隔的路径名，用于标识
资源

此方法将首先在父类装入器中搜索
资源；如果父级为null，则类装入器内置的路径为空
搜索到虚拟机。如果失败，这种方法将
调用findResource（字符串）以查找资源

由于这种通用性，代码更具可移植性，无论您是在Windows还是Linux上，甚至是在某些分布式系统上。有关加载类和可能的源的详细信息：
将文件置于当前文件夹或uri格式

//placing the xml file in the current java file folder(which is not goog way of coding.

DigesterTest ds = (DigesterTest) digest.parse(this.getClass().getResourceAsStream(
             "test.xml"));
DigesterTest ds = (DigesterTest) digest.parse("file://exact location of the file");
//created a xml folder under java project 
DigesterTest ds = (DigesterTest) digest.parse(new File("xml/test.xml"));

将文件置于当前文件夹或uri格式

//placing the xml file in the current java file folder(which is not goog way of coding.

DigesterTest ds = (DigesterTest) digest.parse(this.getClass().getResourceAsStream(
             "test.xml"));
DigesterTest ds = (DigesterTest) digest.parse("file://exact location of the file");
//created a xml folder under java project 
DigesterTest ds = (DigesterTest) digest.parse(new File("xml/test.xml"));

请检查我的异常跟踪文件是否可用！简单地使用“！”：）在getResourceAsStream中使用绝对路径，如果我错了，请纠正我，它是相对于类路径根的。我建议你先把它放在你的src文件夹中，然后慢慢解决，或者你可以选择使用FileInputStream？如果你想坚持绝对文件路径，请检查我的更新问题，即使发送文件对象，它也不起作用。请检查我的异常跟踪文件是否可用！简单地使用“！”：）在getResourceAsStream中使用绝对路径，如果我错了，请纠正我，它是相对于类路径根的。我建议你先把它放在你的src文件夹中，然后慢慢解决，或者你可以选择使用FileInputStream？如果你想坚持绝对文件路径，请检查我更新的问题，即使发送文件对象，它也不起作用。如果
student.xml
文件存在于你的类路径
leo/test/digester/student/
中，那么它应该可以工作！谢谢你的帮助，但是我正在使用EclipseIDE，我试图将文件放在一个位置并