gameVersion改为titleVersion

var gameVersion = "1.8.9";声明变量,指定游戏版本

引入commons-iogson

<dependency>
    <groupId>commons-io</groupId>
    <artifactId>commons-io</artifactId>
    <version>2.8.0</version>
</dependency>
<dependency>
    <groupId>com.google.code.gson</groupId>
    <artifactId>gson</artifactId>
    <version>2.8.6</version>
</dependency>

读取游戏列表访问https://launchermeta.mojang.com/mc/game/version_manifest_v2.json

var gson = new Gson();
        var gameListJson = IOUtils.toString(new URL("https://launchermeta.mojang.com/mc/game/version_manifest_v2.json"), StandardCharsets.UTF_8);
        var gameList = gson.fromJson(gameListJson, JsonObject.class).get("versions").getAsJsonArray();
        var gameJsonURL = "";
        for (JsonElement jsonElement : gameList) {
            if (jsonElement.getAsJsonObject().get("id").getAsString().equals(gameVersion)) {
                gameJsonURL = jsonElement.getAsJsonObject().get("url").getAsString();
            }
        }

        if (gameJsonURL.equals("")) {
            throw new RuntimeException(gameVersion + " Not Found!");
        }

获取versions遍历出所以版本,之后获取指定版本的json

如果没找到版本就抛出异常

var gameJson = gson.fromJson(IOUtils.toString(new URL(gameJsonURL), StandardCharsets.UTF_8), JsonObject.class);
var gameJarUrl = gameJson.get("downloads").getAsJsonObject().get("client").getAsJsonObject().get("url").getAsString();

获取jar文件的url

var versionsDir = new File(gameDir, "versions");

if (!versionsDir.exists()) {
    versionsDir.mkdir();
}

var versionDir = new File(versionsDir, gameVersion);

if (!versionDir.exists()) {
    versionDir.mkdir();
}

var gameJarFile = new File(versionDir,gameVersion + ".jar");

获取本地的Jar路径

if (!gameJarFile.exists()) {
    FileUtils.writeByteArrayToFile(gameJarFile, IOUtils.toByteArray(new URL(gameJarUrl)));
}

如果没有这个文件那么就下载

var gameDir = new File(".",".minecraft");

修改游戏目录为当前目录下的.minecraft