如何使用GSon进行配置?读卡器出错，使用其他方法生成cfg

Question

我尝试用Gson进行配置，我做了这个代码的例子：

    Channel c = new Channel(3, "TEST STRING!");
    Gson gson = new GsonBuilder().create();
    FileWriter writer = new FileWriter("config.json");
    gson.toJson(c, writer);
    writer.flush();
    Reader reader = new InputStreamReader(Bot.class.getResourceAsStream("config.json"), "UTF - 8");
    Gson ab = new GsonBuilder().create();
    Channel a = ab.fromJson(reader, Channel.class);
    System.out.println(a);

但我有错误：java.lang.NullPointerException在线

Reader reader = new InputStreamReader(Bot.class.getResourceAsStream("config.json"), "UTF - 8");

我哪里搞错了？

另一个问题，如何在文件中进行配置？

Answer 1

选项一：您正在读取的文件不能在运行时创建，您可以在开发环境中手动创建它，就像创建java源文件一样。这样它就可以在类路径上，通过getResourceAsStream():提供给您

项目布局：

MyProject
└── src
    └── config.json // option one
    └── com
        └── myproject
            └── Main.java
            └── config.json // option two

您的代码：

// If you placed config.json at location 1 (notice the leading slash)
Reader reader = new InputStreamReader(Bot.class.getResourceAsStream("/config.json"), "UTF - 8");
// If you placed config.json at location 2 (notice no leading slash)
Reader reader = new InputStreamReader(Bot.class.getResourceAsStream("config.json"), "UTF - 8");
Gson ab = new GsonBuilder().create();
Channel a = ab.fromJson(reader, Channel.class);
System.out.println(a);

---

选项二：这可能是你问题的解决方案，但我想我会澄清getResourceAsStream()的作用。与其尝试在类路径上查找config.json，不如从刚保存到的文件中再次加载它。

// You might need to add this import
import java.nio.charset.StandardCharsets;
/*
 * THIS BLOCK SAVES THE `Channel` INSTANCE TO THE FILE `config.json`
 */
// I also fixed this. Always specify your encodings!
try(FileOutputStream fos = new FileOutputStream("config.json");
    OutputStreamWriter osw = new OutputStreamWriter(fos, StandardCharsets.UTF_8);
    BufferedWriter writer = new BufferedWriter(osw))
{
    Channel c = new Channel(3, "TEST STRING!");
    Gson gson = new GsonBuilder().create();
    gson.toJson(c, writer);
} // This is a "try-with-resources" statement. The Closeable resource defined in the try() block will automatically be closed at the end of the try block.
/*
 * THIS BLOCK RECONSTRUCTS THE JUST SAVED `Channel` instance from the file `config.json`
 */
// This opens the file 'config.json' in the working directory of the running program
try(FileInputStream fis = new FileInputStream("config.json");
    InputStreamReader isr = new InputStreamReader(fis, StandardCharsets.UTF_8);
    BufferedReader reader = new BufferedReader(isr))
{
    Gson ab = new GsonBuilder().create();
    Channel a = ab.fromJson(reader, Channel.class);
    System.out.println(a);
} // Again, a try-with-resources statement