java文件读取与输出到文件

文件读取需要找到文件具体在什么地方，有相对路径和绝对路径；

绝对路径就是相对于操作系统的路径，比如在windows下的D:\XX\file.txt；

相对路径则是针对想在运行的项目环境的路径，可以执行类可以通过项目所在的容器环境找到文件；

相对路径简单可以分为两种情况：

一、从项目根目录下寻找

File file = new File("conf/mixpanel.xml");
FileInputStream fi = new FileInputStream("conf/log4j.properties");

二、通过ClassLoader利用类加载的加载路径进行寻找

AppTest.class.getClassLoader().getResourceAsStream("config.xml");
AppTest.class.getClassLoader().getResource("config.xml");

 /**
     * 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.
     *
     * <p> The name of a resource is a '<tt>/</tt>'-separated path name that
     * identifies the resource.
     *
     * <p> This method will first search the parent class loader for the
     * resource; if the parent is <tt>null</tt> the path of the class loader
     * built-in to the virtual machine is searched.  That failing, this method
     * will invoke {@link #findResource(String)} to find the resource.  </p>
     *
     * @param  name
     *         The resource name
     *
     * @return  A <tt>URL</tt> object for reading the resource, or
     *          <tt>null</tt> if the resource could not be found or the invoker
     *          doesn't have adequate  privileges to get the resource.
     *
     * @since  1.1
     */
    public URL getResource(String name) {
        URL url;
        if (parent != null) {
            url = parent.getResource(name);
        } else {
            url = getBootstrapResource(name);
        }
        if (url == null) {
            url = findResource(name);
        }
        return url;
    }

文件输出：

FileOutputStream fos = new FileOutputStream("");
fos.write(CellUtil.cloneQualifier(cell));
fos.write(Bytes.toBytes("="));
fos.write(CellUtil.cloneValue(cell));
fos.write(Bytes.toBytes("\r\n"));
fos.close();

 如果文件输出的路径不存在，需要进行创建；