1. Bean依賴關係

　　一個配置類的Bean，一個例項Bean；

　　例項Bean初始化時需要依賴配置類的Bean；

1.1 配置類Bean

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

    private Integer type;

    private String rootPath;
}

1.2 例項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 {
            // 此處 config 空指標異常
            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. 問題現象

　　例項Bean初始化時配置類Bean空指標異常；

3. 解決方案

3.1 方案一

　　構造器中將Bean作為引數顯式的傳入；

@Component
public class HDFSFileHandler implements FileHandler {

    private SystemConfig config;

    private FileSystem fileSystem;
　　// 構造器顯式傳入引數
    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);
        }
    }
}