Spring 中初始化一个Bean对象时依赖其他Bean对象空指针异常

1. Bean依赖关系

　　一个配置类的Bean，一个实例Bean；

　　实例Bean初始化时需要依赖配置类的Bean；

1.1 配置类Bean

@ConfigurationProperties(prefix = "system")
public class SystemConfig {

    private Integer type;

    private String rootPath;
}

1.2 实例Bean

@Component
public class HDFSFileHandler implements FileHandler {

    @Autowired
    private SystemConfig config;

    private FileSystem fileSystem;

    public HDFSFileHandler(){
        start();
    }

    /**
     * 初始化 fileSystem
     */
    private void start()  {
        try {
            // 此处 config 空指针异常
            if (SystemConstant.FILE_SYSTEM_HDFS.equals(config.getType())){
                String uri = "hdfs://" + config.getHdfsIp() + ":" + config.getHdfsPort();
                fileSystem = FileSystem.get(new URI(uri), new Configuration(), "hadoop");
                log.debug("uri:" + uri);
                log.debug("fileSystem:" + fileSystem);
            }
        } catch (Exception e) {
            log.error("init fileSystem occur a exception",e);
        }
    }
}

2. 问题现象

　　实例Bean初始化时配置类Bean空指针异常；

　　

3. 解决方案

3.1 方案一

　　构造器中将Bean作为参数显式的传入；

@Component
public class HDFSFileHandler implements FileHandler {

    private SystemConfig config;

    private FileSystem fileSystem;
　　// 构造器显式传入参数
    public HDFSFileHandler(SystemConfig config) {
        this.config = config;
        start();
    }

    /**
     * 初始化 fileSystem
     */
    private void start()  {
        try {
            
            if (SystemConstant.FILE_SYSTEM_HDFS.equals(config.getType())){
                String uri = "hdfs://" + config.getHdfsIp() + ":" + config.getHdfsPort();
                fileSystem = FileSystem.get(new URI(uri), new Configuration(), "hadoop");
                log.debug("uri:" + uri);
                log.debug("fileSystem:" + fileSystem);
            }
        } catch (Exception e) {
            log.error("init fileSystem occur a exception",e);
        }
    }
}

3.2  @Autowired + @PostConstruct

@Component
public class HDFSFileHandler implements FileHandler {

    @Autowired
    private SystemConfig config;

    private FileSystem fileSystem;

    public HDFSFileHandler() {
        start();
    }

    /**
     * 初始化 fileSystem
     */
    @PostConstruct
    private void start()  {
        try {
            if (SystemConstant.FILE_SYSTEM_HDFS.equals(config.getType())){
                String uri = "hdfs://" + config.getHdfsIp() + ":" + config.getHdfsPort();
                fileSystem = FileSystem.get(new URI(uri), new Configuration(), "hadoop");
                log.debug("uri:" + uri);
                log.debug("fileSystem:" + fileSystem);
            }
        } catch (Exception e) {
            log.error("init fileSystem occur a exception",e);
        }
    }
}