java - 如何使用GSon进行配置？阅读器出错，还有其他方式制作cfg吗？

Question

我尝试使用 Gson 进行配置我制作了以下代码示例:

    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 排队

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

我哪里出错了？

另一个问题，如何在文件中进行配置？

Answer 1

选项一:您正在读取的文件无法在运行时创建，您需要在开发环境中手动创建它，就像创建 java 源文件一样。这样它就可以位于类路径上，您可以通过 getResourceAsStream() 获取:

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);

<小时/>

选项二:这可能是您问题的解决方案，但我想我应该澄清 getResourceAsStream() 的作用。不要尝试在类路径上查找 config.json，而是从刚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