getResource(String name)用法及源码分析

Project获取资源需要一个启点，加载资源的动作是由ClassLoader来完成的。
Class对象和当前线程对象可以找到当前加载资源的ClassLoader，
通过ClassLoader的getResource(String name)方法及其它衍生出来的方法可以找到Application的启点及获取相关资源

    
private void display() {
        path=this.getClass().getResource("/loadresource").getPath();
        System.out.println(path);
        path=this.getClass().getResource("/loadresource/bp.txt").getPath();
        System.out.println(path);
        path=this.getClass().getResource("/").getPath();
        System.out.println(path);
        URL url=this.getClass().getResource("loadresource/bp.txt");
        System.out.println("Is Null:"+(url==null));
        
        path=GetResouceTest.class.getClassLoader().getResource("").getPath();
        System.out.println(path);
        path=GetResouceTest.class.getClassLoader().getResource("loadresource/bp.txt").getPath();
        System.out.println(path);
        url=GetResouceTest.class.getClassLoader().getResource("/loadresource/bp.txt");
        System.out.println("Is Null:"+(url==null));
        
        
        path=Thread.currentThread().getContextClassLoader().getResource("").getPath();
        System.out.println(path);
        path=Thread.currentThread().getContextClassLoader().getResource("loadresource/bp.txt").getPath();
        System.out.println(path);
        url=Thread.currentThread().getContextClassLoader().getResource("loadresource/bp.txt");
        System.out.println("Is Null:"+(url==null));
        url=Thread.currentThread().getContextClassLoader().getResource("/loadresource/bp.txt");
        System.out.println("Is Null:"+(url==null));
        
    }

/E:/java/workspace/test/bin/loadresource
/E:/java/workspace/test/bin/loadresource/bp.txt
/E:/java/workspace/test/bin/
Is Null:true
/E:/java/workspace/test/bin/
/E:/java/workspace/test/bin/loadresource/bp.txt
Is Null:true
/E:/java/workspace/test/bin/
/E:/java/workspace/test/bin/loadresource/bp.txt
Is Null:false
Is Null:true

 /**
     * Finds a resource with a given name.  The rules for searching resources
     * associated with a given class are implemented by the defining
     * {@linkplain ClassLoader 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 {@link
     * ClassLoader#getSystemResource}.
     *
     * <p> Before delegation, an absolute resource name is constructed from the
     * given resource name using this algorithm:
     *
     * <ul>
     *
     * <li> If the {@code name} begins with a {@code '/'}
     * (<tt>'&#92;u002f'</tt>), then the absolute name of the resource is the
     * portion of the {@code name} following the {@code '/'}.
     *
     * <li> Otherwise, the absolute name is of the following form:
     *
     * <blockquote>
     *   {@code modified_package_name/name}
     * </blockquote>
     *
     * <p> Where the {@code modified_package_name} is the package name of this
     * object with {@code '/'} substituted for {@code '.'}
     * (<tt>'&#92;u002e'</tt>).
     *
     * </ul>
     *
     * @param  name name of the desired resource
     * @return      A  {@link java.net.URL} object or {@code null} if no
     *              resource with this name is found
     * @since  JDK1.1
     */
    public java.net.URL getResource(String name) {
        name = resolveName(name);
        ClassLoader cl = getClassLoader0();
        if (cl==null) {
            // A system class.
            return ClassLoader.getSystemResource(name);
        }
        return cl.getResource(name);
    }

   /**
     * Add a package name prefix if the name is not absolute Remove leading "/"
     * if name is absolute
     */
    private String resolveName(String name) {
        if (name == null) {
            return name;
        }
        if (!name.startsWith("/")) {
            Class<?> c = this;
            while (c.isArray()) {
                c = c.getComponentType();
            }
            String baseName = c.getName();
            int index = baseName.lastIndexOf('.');
            if (index != -1) {
                name = baseName.substring(0, index).replace('.', '/')
                    +"/"+name;
            }
        } else {
            name = name.substring(1);
        }
        return name;
    }