0

请帮助我知道我的代码有什么问题。我从这个链接尝试了示例。操作系统：Windows 7

代码 1：

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

例外一：

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)

代码 2：

 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);

例外 2：

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)

学生.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);
}
}

学生.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>

DigestStudents.java

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 );
    }
}
4

6 回答 6

1

我认为这条线是有问题的：

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。

于 2013-09-13T07:33:15.280 回答
1

ClassLoader.getResourceAsStream 在您的类路径中查找文件。将您的 getResourceAsStream 更改为：

.getResourceAsStream("student.xml"));

确保指定路径

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

在您的类路径中，然后重新编译并再次运行它。

于 2013-09-13T07:40:18.877 回答
1

两者都getResource适用getResourceAsStream于相对于类路径的 URI。

您需要将路径修改为类似于以下内容的内容

getResourceAsStream("/leo/test/digester/student/student.xml");
于 2013-09-13T07:40:42.430 回答
1

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"));

和

 DigestStudents ds = (DigestStudents) digester.parse(this.getClass()
                       .getClassLoader()
                       .getResourceAsStream("leo/test/digester/student/student.xml"));
于 2013-09-13T07:41:34.473 回答
1

获取加载我们类的对象的整个想法是能够独立于当前系统设置，从当前绝对路径获取资源。getResourceAsStream因为找不到文件，所以您输入 null 。只需student.xml按照 Kayaman 的建议创建相对路径或绝对路径即可。

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

classLoader.getResourceAsStream您使用与加载当前类相同的路径搜索顺序来获取文件。请参阅 javadoc 获取 getResource：

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

查找具有给定名称的资源。资源是可以由类代码以独立于代码位置的方式访问的一些数据（图像、音频、文本等）。

资源的名称是一个以“/”分隔的路径名，用于标识该资源。

该方法将首先在父类加载器中搜索资源；如果 parent 为 null，则搜索虚拟机内置的类加载器的路径。如果失败，此方法将调用 findResource(String) 来查找资源。

由于这种概括，代码更具可移植性，无论您是在 Windows 还是 Linux 上，甚至在某些分布式系统上都无关紧要。更多关于加载类和可能的来源：java.lang.ClassLoader

于 2013-09-13T08:10:46.467 回答
0

将文件放在当前文件夹或 uri 格式中。

//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"));
于 2014-03-13T09:13:57.713 回答