Question

我正在构建REST API，我有访问器

    @Accessor
public interface ActiveBidAccessor {
    @Query("SELECT * FROM keyspace.active_bid WHERE username = :username")
    public Result<ActiveBid> getAllByUsersname(@Param("username") String username);


    @Query("SELECT * FROM keyspace.active_bid")
    public Result<ActiveBid> getAll();
}

和ActiveBid类

@Table(keyspace = "keyspace", name = "active_bid", readConsistency = "QUORUM", writeConsistency = "QUORUM", caseSensitiveKeyspace = false, caseSensitiveTable = false)
public class ActiveBid {
    @PartitionKey
    UUID uid;
    @ClusteringColumn
    @Column(name = "username")
    String username;
    @Column(name = "project_name")
    String projectName;
    @Column(name = "project_link")
    String projectLink;
    @Column(name = "total_bid")
    int totalBid;
    @Column(name = "user_bid")
    long userBid;
    @Column(name = "avg_bid")
    long avgBid;
    @Column(name = "end_date")
    Date endDate;

    public ActiveBid(UUID uid, String username, String projectName, String projectLink, int totalBid, long userBid,
            long avgBid, Date endDate) {
        super();
        this.uid = uid;
        this.username = username;
        this.projectName = projectName;
        this.projectLink = projectLink;
        this.totalBid = totalBid;
        this.userBid = userBid;
        this.avgBid = avgBid;
        this.endDate = endDate;
    }

    public UUID getUid() {
        return uid;
    }

    public void setUid(UUID uid) {
        this.uid = uid;
    }

    public String getUsername() {
        return username;
    }

    public void setUsername(String username) {
        this.username = username;
    }

    public String getProjectName() {
        return projectName;
    }

    public void setProjectName(String projectName) {
        this.projectName = projectName;
    }

    public String getProjectLink() {
        return projectLink;
    }

    public void setProjectLink(String projectLink) {
        this.projectLink = projectLink;
    }

    public int getTotalBid() {
        return totalBid;
    }

    public void setTotalBid(int totalBid) {
        this.totalBid = totalBid;
    }

    public long getUserBid() {
        return userBid;
    }

    public void setUserBid(long userBid) {
        this.userBid = userBid;
    }

    public long getAvgBid() {
        return avgBid;
    }

    public void setAvgBid(long avgBid) {
        this.avgBid = avgBid;
    }

    public Date getEndDate() {
        return endDate;
    }

    public void setEndDate(Date endDate) {
        this.endDate = endDate;
    }

    @Override
    public int hashCode() {
        return Objects.hashCode(uid, username, projectName, projectLink, totalBid, userBid, avgBid, endDate);
    }

    @Override
    public boolean equals(Object obj) {
        if (obj instanceof ActiveBid) {
            ActiveBid that = (ActiveBid) obj;
            return Objects.equal(this.uid, that.uid) && Objects.equal(this.username, that.username)
                    && Objects.equal(this.projectName, that.projectName)
                    && Objects.equal(this.projectLink, that.projectLink) && Objects.equal(this.totalBid, that.totalBid)
                    && Objects.equal(this.userBid, that.userBid) && Objects.equal(this.avgBid, that.avgBid)
                    && Objects.equal(this.endDate, that.endDate);
        }
        return false;
    }

和我的球衣请求映射器，其中包含获取数据的逻辑

@GET
@Path("/get")
@Produces(MediaType.APPLICATION_JSON)
public List<ActiveBid> getTrackInJSON() {
    logger.info("LoginApi: Returning the active bid");
    List<ActiveBid> activeBidList = new ArrayList<ActiveBid>();

    MappingManager manager = new MappingManager(cassDB.getSession());
    ActiveBidAccessor activeBidAccessor = manager.createAccessor(ActiveBidAccessor.class);
    Result<ActiveBid> activeBidResult = activeBidAccessor.getAllByUsersname("zakir");
    for(ActiveBid bid:activeBidResult){
        activeBidList.add(bid);
    }

    return activeBidList;
}

我收到以下错误

引起：java.lang.RuntimeException：无法创建实例 com.xyz.v1.ActiveBid at com.datastax.driver.mapping.ReflectionMapper.newEntity（ReflectionMapper.java:47）在com.datastax.driver.mapping.Result.map（Result.java:40）at com.datastax.driver.mapping.Result.one（Result.java:87）at com.datastax.driver.mapping.Mapper $ 1.apply（Mapper.java:82）at com.datastax.driver.mapping.Mapper $ 1.apply（Mapper.java:79）at com.google.common.util.concurrent.Futures $ 1.适用（Futures.java:713）在 com.google.common.util.concurrent.Futures $ ChainingListenableFuture.run（Futures.java:861）在 com.google.common.util.concurrent.MoreExecutors $ SameThreadExecutorService.execute（MoreExecutors.java:297）在 com.google.common.util.concurrent.ExecutionList.executeListener（ExecutionList.java:156）在 com.google.common.util.concurrent.ExecutionList.execute（ExecutionList.java:145）在 com.google.common.util.concurrent.AbstractFuture.set（AbstractFuture.java:185）在 com.google.common.util.concurrent.Futures $ ChainingListenableFuture $ 1.run（Futures.java:872）在 com.google.common.util.concurrent.MoreExecutors $ SameThreadExecutorService.execute（MoreExecutors.java:297）在 com.google.common.util.concurrent.ExecutionList.executeListener（ExecutionList.java:156）在 com.google.common.util.concurrent.ExecutionList.execute（ExecutionList.java:145）在 com.google.common.util.concurrent.AbstractFuture.set（AbstractFuture.java:185）在 com.datastax.driver.core.DefaultResultSetFuture.onSet（DefaultResultSetFuture.java:174）在 com.datastax.driver.core.RequestHandler.setFinalResult（RequestHandler.java:177）在 com.datastax.driver.core.RequestHandler.access $ 2500（RequestHandler.java:43）在 com.datastax.driver.core.RequestHandler $ SpeculativeExecution.setFinalResult（RequestHandler.java:792）在 com.datastax.driver.core.RequestHandler $ SpeculativeExecution.onSet（RequestHandler.java:467）在 com.datastax.driver.core.Connection $ Dispatcher.channelRead0（Connection.java:1013）在 com.datastax.driver.core.Connection $ Dispatcher.channelRead0（Connection.java:936）在 io.netty.channel.SimpleChannelInboundHandler.channelRead（SimpleChannelInboundHandler.java:105）在 io.netty.channel.AbstractChannelHandlerContext.invokeChannelRead（AbstractChannelHandlerContext.java:318）在 io.netty.channel.AbstractChannelHandlerContext.fireChannelRead（AbstractChannelHandlerContext.java:304）在 io.netty.handler.timeout.IdleStateHandler.channelRead（IdleStateHandler.java:266）在 io.netty.channel.AbstractChannelHandlerContext.invokeChannelRead（AbstractChannelHandlerContext.java:318）在 io.netty.channel.AbstractChannelHandlerContext.fireChannelRead（AbstractChannelHandlerContext.java:304）在 io.netty.handler.codec.MessageToMessageDecoder.channelRead（MessageToMessageDecoder.java:103）在 io.netty.channel.AbstractChannelHandlerContext.invokeChannelRead（AbstractChannelHandlerContext.java:318）在 io.netty.channel.AbstractChannelHandlerContext.fireChannelRead（AbstractChannelHandlerContext.java:304）在 io.netty.handler.codec.ByteToMessageDecoder.fireChannelRead（ByteToMessageDecoder.java:276）在 io.netty.handler.codec.ByteToMessageDecoder.channelRead（ByteToMessageDecoder.java:263）在 io.netty.channel.AbstractChannelHandlerContext.invokeChannelRead（AbstractChannelHandlerContext.java:318）在 io.netty.channel.AbstractChannelHandlerContext.fireChannelRead（AbstractChannelHandlerContext.java:304）在 io.netty.channel.DefaultChannelPipeline.fireChannelRead（DefaultChannelPipeline.java:846）在 io.netty.channel.nio.AbstractNioByteChannel $ NioByteUnsafe.read（AbstractNioByteChannel.java:131）在 io.netty.channel.nio.NioEventLoop.processSelectedKey（NioEventLoop.java:511）在 io.netty.channel.nio.NioEventLoop.processSelectedKeysOptimized（NioEventLoop.java:468）在 io.netty.channel.nio.NioEventLoop.processSelectedKeys（NioEventLoop.java:382）在io.netty.channel.nio.NioEventLoop.run（NioEventLoop.java:354）at io.netty.util.concurrent.SingleThreadEventExecutor $ 2.run（SingleThreadEventExecutor.java:112） ......还有1个

有人可以帮我解决这个问题吗，我不知道Cassandra会不会这么做。

Answer 1

驱动程序不善于报告异常原因。 stacktrace points to this

@Override
public T newEntity() {
    try {
        return entityClass.newInstance();
    } catch (Exception e) {
        throw new RuntimeException("Can't create an instance of " + entityClass.getName());
    }
}

不幸吞下了这个例外。

同样，读取该代码时，似乎发生异常，因为您的实体类中没有可访问的无参数构造函数。

只需添加一个

public ActiveBid() {}

文档here并未明确说明，但所有示例都使用此类构造函数。

Answer 2

经典问题，您的班级ActiveBid应尊重Java Beans惯例，例如提供默认（public＆amp; no arg）构造函数

Cassandra映射器未映射到类

2 个答案: