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some utility class for java develop
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package com.star.io.resource;

import com.star.clazz.ClassLoaderUtil;
import com.star.io.file.PathUtil;
import com.star.lang.Assert;
import com.star.string.StringUtil;

import java.net.URL;
import java.nio.file.Paths;

/**
 * ClassPath单一资源访问类

 * 传入路径path必须为相对路径，如果传入绝对路径，Linux路径会去掉开头的“/”，而Windows路径会直接报错。

 * 传入的path所指向的资源必须存在，否则报错
 *
 * @author Looly
 */
public class ClassPathResource extends UrlResource {

    private String path;
    private ClassLoader classLoader;
    private Class clazz;

    // -------------------------------------------------------------------------------------- Constructor start

    /**
     * 构造
     *
     * @param path 相对于ClassPath的路径
     */
    public ClassPathResource(String path) {
        this(path, null, null);
    }

    /**
     * 构造
     *
     * @param path        相对于ClassPath的路径
     * @param classLoader {@link ClassLoader}
     */
    public ClassPathResource(String path, ClassLoader classLoader) {
        this(path, classLoader, null);
    }

    /**
     * 构造
     *
     * @param path  相对于给定Class的路径
     * @param clazz {@link Class} 用于定位路径
     */
    public ClassPathResource(String path, Class clazz) {
        this(path, null, clazz);
    }

    /**
     * 构造
     *
     * @param pathBaseClassLoader 相对路径
     * @param classLoader         {@link ClassLoader}
     * @param clazz               {@link Class} 用于定位路径
     */
    public ClassPathResource(String pathBaseClassLoader, ClassLoader classLoader, Class clazz) {
        super((URL) null);
        Assert.notNull(pathBaseClassLoader, "Path must not be null");
        this.path = normalizePath(pathBaseClassLoader);
        this.classLoader = (classLoader != null) ? classLoader : ClassLoaderUtil.getClassLoader();
        this.clazz = clazz;
        initUrl();
    }
    // -------------------------------------------------------------------------------------- Constructor end

    /**
     * 获得Path
     *
     * @return path
     */
    public final String getPath() {
        return this.path;
    }

    /**
     * 获得绝对路径Path

     * 对于不存在的资源，返回拼接后的绝对路径
     *
     * @return 绝对路径path
     */
    public final String getAbsolutePath() {
        if (Paths.get(path).isAbsolute()) {
            return this.path;
        }
        // url在初始化的时候已经断言，此处始终不为null
        return PathUtil.getPath(url).normalize().toString();
    }

    /**
     * 获得 {@link ClassLoader}
     *
     * @return {@link ClassLoader}
     */
    public final ClassLoader getClassLoader() {
        return this.classLoader;
    }

    /**
     * 根据给定资源初始化URL
     */
    private void initUrl() {
        if (null != this.clazz) {
            super.url = this.clazz.getResource(this.path);
        } else if (null != this.classLoader) {
            super.url = this.classLoader.getResource(this.path);
        } else {
            super.url = ClassLoader.getSystemResource(this.path);
        }
        if (null == super.url) {
            throw new NoResourceException("Resource of path [{}] not exist!", this.path);
        }
    }

    @Override
    public String toString() {
        return (null == this.path) ? super.toString() : "classpath:" + this.path;
    }

    /**
     * 标准化Path格式
     *
     * @param path Path
     * @return 标准化后的path
     */
    private String normalizePath(String path) {
        // 标准化路径
        path = Paths.get(path).normalize().toString();
        path = StringUtil.removePrefix(path, StringUtil.SLASH, true);

        Assert.isTrue(!Paths.get(path).isAbsolute(), "Path must be a relative path !");
        return path;
    }
}