Java中解析嵌套YAML配置：使用Jackson进行对象映射

# Servlet MCD configuration file
app:
  buildRpmPath: /home/jkerich/Software/buildrpm/
  rootConfigurationPath: /home/jkerich/Software/RTConfigurationFiles/

import java.io.FileInputStream;
import java.io.InputStream;
import java.util.Map;
import org.yaml.snakeyaml.Yaml;

public class YamlParserProblem {
    public static void main(String[] args) {
        String defaultPath = "config.yaml"; // 假设这是你的YAML文件路径
        Yaml yaml = new Yaml();
        InputStream inputStream = null;
        try {
            inputStream = new FileInputStream(defaultPath);
            Map<String, Object> yamlMaps = yaml.load(inputStream);
            System.out.println("解析后的Map: " + yamlMaps);
            // 尝试直接链式调用，这将导致编译错误或运行时ClassCastException
            // buildRpmPath = yamlMaps.get("app").get("buildRpmPath").toString();
            // 错误原因：yamlMaps.get("app")返回的是Object类型，Object没有get方法。
            // 即使强制转换为Map，也可能因为泛型不匹配导致警告或运行时错误。
        } catch (Exception e) {
            e.printStackTrace();
        } finally {
            if (inputStream != null) {
                try {
                    inputStream.close();
                } catch (Exception e) {
                    e.printStackTrace();
                }
            }
        }
    }
}

<dependencies>
    <dependency>
        <groupId>com.fasterxml.jackson.core</groupId>
        <artifactId>jackson-databind</artifactId>
        <version>2.13.4</version> <!-- 请使用最新稳定版本 -->
    </dependency>
    <dependency>
        <groupId>com.fasterxml.jackson.dataformat</groupId>
        <artifactId>jackson-dataformat-yaml</artifactId>
        <version>2.13.4</version> <!-- 请使用最新稳定版本 -->
    </dependency>
</dependencies>

app:
  buildRpmPath: /home/jkerich/Software/buildrpm/
  rootConfigurationPath: /home/jkerich/Software/RTConfigurationFiles/

package com.example.config;

public class AppConfig {
    private String buildRpmPath;
    private String rootConfigurationPath;

    // 无参构造函数是Jackson反序列化所必需的
    public AppConfig() {}

    public String getBuildRpmPath() {
        return buildRpmPath;
    }

    // Jackson会通过setter方法将YAML中的值注入到字段中
    // 注意：setter方法名应遵循Java Bean规范，与YAML键名（驼峰命名）对应
    public void setBuildRpmPath(String buildRpmPath) {
        this.buildRpmPath = buildRpmPath;
    }

    public String getRootConfigurationPath() {
        return rootConfigurationPath;
    }

    public void setRootConfigurationPath(String rootConfigurationPath) {
        this.rootConfigurationPath = rootConfigurationPath;
    }

    @Override
    public String toString() {
        return "AppConfig{" +
               "buildRpmPath='" + buildRpmPath + '\'' +
               ", rootConfigurationPath='" + rootConfigurationPath + '\'' +
               '}';
    }
}

package com.example.config;

public class ApplicationConfiguration {
    private AppConfig app; // 对应YAML中的'app'键

    public ApplicationConfiguration() {}

    public AppConfig getApp() {
        return app;
    }

    public void setApp(AppConfig app) {
        this.app = app;
    }

    @Override
    public String toString() {
        return "ApplicationConfiguration{" +
               "app=" + app +
               '}';
    }
}

package com.example;

import com.example.config.ApplicationConfiguration;
import com.fasterxml.jackson.databind.ObjectMapper;
import com.fasterxml.jackson.dataformat.yaml.YAMLFactory;

import java.io.File;
import java.io.IOException;

public class YamlParserSolution {
    public static void main(String[] args) {
        String yamlFilePath = "config.yaml"; // 假设你的YAML文件名为config.yaml

        ObjectMapper mapper = new ObjectMapper(new YAMLFactory());
        try {
            // 从文件读取YAML并映射到ApplicationConfiguration对象
            ApplicationConfiguration config = mapper.readValue(new File(yamlFilePath), ApplicationConfiguration.class);

            // 现在可以类型安全地访问配置值
            if (config != null && config.getApp() != null) {
                String buildRpmPath = config.getApp().getBuildRpmPath();
                String rootConfigurationPath = config.getApp().getRootConfigurationPath();

                System.out.println("Build RPM Path: " + buildRpmPath);
                System.out.println("Root Configuration Path: " + rootConfigurationPath);
            } else {
                System.out.println("无法加载或解析YAML配置。");
            }

        } catch (IOException e) {
            System.err.println("解析YAML文件时发生错误: " + e.getMessage());
            e.printStackTrace();
        }
    }
}