Class.getResourceAsStream() VS. ClassLoader.getResourceAsStream()

For Class.getResourceAsStream(String name), 
  • if the name parameter doesn‘t start with a "/", then it‘s a relative path to the class‘s package.
  • If the name parameter starts with a "/", then it‘s an absolute path.
For ClassLoader.getResourceAsStream(String name), 
  • the name parameter is always an absolute path.
  • and it can never start with a "/",if it does, the resource is never found.

If the file cannot be found, both methods return null and no exception is thrown.

The following program illustrates the difference.

Project structure

ResourceAsStream.java
public class ResourceAsStream {

    /**
     * @param args
     */
    public static void main(String[] args) {
        String path1 = "a.properties";
        String path2 = "/a.properties";
        String path3 = "test/a.properties";
        String path4 = "/test/a.properties";

        System.out.println("Class.getResourceAsStream()");
        InputStream is = ResourceAsStream.class.getResourceAsStream(path1);
        System.out.println(path1 + " " + (is != null));
        is = ResourceAsStream.class.getResourceAsStream(path2);
        System.out.println(path2 + " " + (is != null));
        is = ResourceAsStream.class.getResourceAsStream(path3);
        System.out.println(path3 + " " + (is != null));
        is = ResourceAsStream.class.getResourceAsStream(path4);
        System.out.println(path4 + " " + (is != null));
        System.out.println();
        System.out.println("ClassLoader.getResourceAsStream()");
        is = ResourceAsStream.class.getClassLoader().getResourceAsStream(path1);
        System.out.println(path1 + " " + (is != null));
        is = ResourceAsStream.class.getClassLoader().getResourceAsStream(path2);
        System.out.println(path2 + " " + (is != null));
        is = ResourceAsStream.class.getClassLoader().getResourceAsStream(path3);
        System.out.println(path3 + " " + (is != null));
        is = ResourceAsStream.class.getClassLoader().getResourceAsStream(path4);
        System.out.println(path4 + " " + (is != null));
    }
}
Result:
Class.getResourceAsStream()
a.properties true
/a.properties false
test/a.properties false
/test/a.properties true

ClassLoader.getResourceAsStream()
a.properties false
/a.properties false
test/a.properties true
/test/a.properties false

JDK explanation about this two method

Class.java

public InputStream getResourceAsStream(String name)

Finds a resource with a given name. The rules for searching resources associated with a given class are implemented by the defining class loader of the class. This method delegates to this object‘s class loader. If this object was loaded by the bootstrap class loader, the method delegates to ClassLoader.getSystemResourceAsStream(java.lang.String).

Before delegation, an absolute resource name is constructed from the given resource name using this algorithm:

    • If the name begins with a ‘/‘ (‘\u002f‘), then the absolute name of the resource is the portion of the name following the ‘/‘.
    • Otherwise, the absolute name is of the following form:

      modified_package_name/name

      Where the modified_package_name is the package name of this object with ‘/‘ substituted for ‘.‘ (‘\u002e‘).

Parameters:
name - name of the desired resource
Returns:
InputStream object or null if no resource with this name is found
Throws:
NullPointerException - If name is null

ClassLoader.java

public InputStream getResourceAsStream(String name)
Returns an input stream for reading the specified resource.
The search order is described in the documentation for getResource(String).
Parameters:
    name - The resource name
Returns:
    An input stream for reading the resource, or null if the resource could not be found
Since:
    1.1

public URL getResource(String name)
Finds the resource with the given name. A resource is some data (images, audio, text, etc) that can be accessed by class code in a way that is independent of the location of the code.
The name of a resource is a ‘/‘-separated path name that identifies the resource. --here it means absolute path

This method will first search the parent class loader for the resource; if the parent is null the path of the class loader built-in to the virtual machine is searched. That failing, this method will invokefindResource(String) to find the resource.

Parameters:
name - The resource name
    Returns:
A URL object for reading the resource, or null if the resource could not be found or the invoker doesn‘t have adequate privileges to get the resource.
    Since:
1.1

below from http://www.javaworld.com/article/2077404/core-java/got-resources-.html

Because Class.getResource() eventually delegates toClassLoader.getResource(), the two methods are indeed very similar.

However, the first method is often preferable. It provides a nice extra feature: it looks up package-local resources.

As an example, this code snippet getClass().getResource("settings.properties"); executed from a class some.pkg.MyClass

looks for a resource deployed a ssome/pkg/settings.properties.You might wonder why this is better then the equivalent

getClass().getClassLoader().getResource("some/pkg/settings.properties");

The reason is the possibility for future refactoring. Should you decide to rename pkgto betterpkgname and move all classes and resources into the new

package, the first code snippet requires no further code changes. The second code snippet embeds the old package name in a string literal—something that

is easy to forget and can become a runtime error later. Another advantage of Class.getResource() is that it does not require thegetClassLoader runtime

security permission, which the other approach requires.

I should mention a few extra details. Is it better to acquire the relevant Class object using the getClass() instance method or using MyClass.class?

The answer depends on whether you plan to have classes in other packages extend MyClass.

Since get Class() always returns the most derived class, it might return a class in a package different from some.pkg, possibly coded after MyClass is

conceived. If this is a possibility, you should safeguard against potential lookup errors by using the class literal syntax form, MyClass.class. As an added

benefit, it also works from static methods.

Class.getResourceAsStream() VS. ClassLoader.getResourceAsStream()

时间: 2024-10-09 06:33:43

Class.getResourceAsStream() VS. ClassLoader.getResourceAsStream()的相关文章

对Class.getResourceAsStream和ClassLoader.getResourceAsStream方法所使用的资源路径的解释 (转)

对Class.getResourceAsStream和ClassLoader.getResourceAsStream方法所使用的资源路径的解释 标签: classgetResourceAsStreampath 2014-08-22 11:21 13675人阅读 评论(0) 收藏 举报 版权声明:本文为博主原创文章,未经博主允许不得转载. 这是个很基础的问题了,这里提供一些示例,帮助快速理解和记忆这个问题. 在该方法的文档:http://docs.oracle.com/javase/7/docs/

Class.getResourceAsStream()和ClassLoader.getResourceAsStream()

Edit Class.getResourceAsStream()和ClassLoader.getResourceAsStream() 注意三点: 1.用Class.getResourceAsStream() 时,路径应该是以"/"开头的,如: mypackage.Hello.class.getResourceAsStream("/config/config.ini"); 2.如果直接用ClassLoader.getResourceAsStream()不用以"

class getResourceAsStream 和 classloader getResourceAsStream获取资源的不同

工程目录结构: prj(工程根目录) cn json classloader GetResourceByClassAndClassLoader.Java beans.xml /** * */ package cn.json.classloader; import java.io.InputStream; /** * @author json * * @date 2014-5-7 * * @version 1.0 */ public class GetResourceByClassAndClass

Class.getResourceAsStream和ClassLoader.getResourceAsStream方法

这是个很基础的问题了,这里提供一些示例,帮助快速理解和记忆这个问题. 在该方法的文档:http://docs.oracle.com/javase/7/docs/api/java/lang/Class.html#getResourceAsStream%28java.lang.String%29 中详细有描述了它接收的路径是如何定义的! 本文原文出处: blog.csdn.net/bluishglc/article/details/38753047 严禁任何形式的转载,否则将委托CSDN官方维护权益

ClassLoader.getResourceAsStream(name); 获取配置文件的方法

ClassLoader.getResourceAsStream(name);路径问题 InputStream in = getClass().getResourceAsStream('/'+"spring-beans.dtd"); 表示从classs目录下面的找文件,文件放在src下面就可以了.InputStream in = getClass().getResourceAsStream("spring-beans.dtd"); 表示从当前classs下面的路径找文

ClassLoader.getResourceAsStream() 加载配置文件资源

JAVA 笔记 ClassLoader.getResourceAsStream() 与 Class.getResourceAsStream()的区别     Class.getResourceAsStream() 会指定要加载的资源路径与当前类所在包的路径一致. 例如你写了一个MyTest类在包com.test.mycode 下,那么MyTest.class.getResourceAsStream("name") 会在com.test.mycode包下查找相应的资源. 如果这个name

ClassLoader.getResourceAsStream() 与 Class.getResourceAsStream()的区别

package com.xinwei.util; import java.io.IOException; import java.io.InputStream; import java.util.Properties; public class PropertiesLoader { public static void main(String[] args) { // test1(); test2(); } //在使用Class.getResourceAsStream 时, 资源路径有两种方式,

JAVA 笔记 ClassLoader.getResourceAsStream() 与 Class.getResourceAsStream()的区别

   Class.getResourceAsStream() 会指定要加载的资源路径与当前类所在包的路径一致. 例如你写了一个MyTest类在包com.test.mycode 下,那么MyTest.class.getResourceAsStream("name") 会在com.test.mycode包下查找相应的资源. 如果这个name是以 '/' 开头的,那么就会从classpath的根路径下开始查找. ClassLoader.getResourceAsStream()  无论要查找

classLoader.getResourceAsStream中文乱码

一直用一个方法安然无恙,今天在新项目中突然乱码了,原代码: ClassLoader classLoader = Thread.currentThread().getContextClassLoader(); InputStream is = null; is = classLoader.getResourceAsStream("config/constant.properties"); if (is != null) { try { props.load(is); } 优化后: sta