转载需注明出处：，

前面一节我们说到了远端事件。其中，市场数据就属于远端事件。市场数据有什么？我们通过代码来回答这个问题：

package org.cryptocoinpartners.schema;import javax.annotation.Nullable;import javax.persistence.Entity;import javax.persistence.ManyToOne;import org.joda.time.Instant;/** * @author Tim Olson */@Entity //实体，在数据库中会创建表格public abstract class MarketData extends RemoteEvent {    protected MarketData(Instant time, @Nullable String remoteKey, Market market) {        this(time, Instant.now(), remoteKey, market);    }    protected MarketData(Instant time, Instant timeReceived, String remoteKey, Market market) {        super(time, timeReceived, remoteKey);        this.market = market;    }    @ManyToOne(optional = false)    public Market getMarket() {        return market;    }    // JPA    protected MarketData() {        super();    }    protected void setMarket(Market market) {        this.market = market;    }    private Market market;//市场}

市场数据里面只有一个成员，市场。也即是说市场数据是某一时刻的市场。

我们接下来看看市场又有什么数据，Market。

我们通过注释代码来学习。

package org.cryptocoinpartners.schema;import java.math.BigDecimal;import java.util.ArrayList;import java.util.Collection;import java.util.List;import javax.persistence.Basic;import javax.persistence.Cacheable;import javax.persistence.Entity;import javax.persistence.Index;import javax.persistence.ManyToOne;import javax.persistence.NamedQuery;import javax.persistence.NoResultException;import javax.persistence.PostPersist;import javax.persistence.Table;import javax.persistence.Transient;import org.cryptocoinpartners.enumeration.FeeMethod;import org.cryptocoinpartners.util.PersistUtil;import org.cryptocoinpartners.util.RemainderHandler;/** * Represents the possibility to trade one Asset for another at a specific Exchange. * * @author Tim Olson */@Entity //表格@Cacheable // 缓存@NamedQuery(name = "Market.findByMarket", query = "select m from Market m where exchange=?1 and listing=?2") // 命名查询@Table(indexes = { @Index(columnList = "exchange"), @Index(columnList = "listing"), @Index(columnList = "active") }) //编织索引public class Market extends EntityBase {    public static Collection
    
      findAll() {//查询所有市场数据        return PersistUtil.queryList(Market.class, "select m from Market m");    }    /** adds the Market to the database if it does not already exist */    public static Market findOrCreate(Exchange exchange, Listing listing) {        return findOrCreate(exchange, listing, listing.getPriceBasis(), listing.getVolumeBasis());    }    @PostPersist    private void postPersist() {        //PersistUtil.detach(this);    }//查询或创建市场数据    public static Market findOrCreate(Exchange exchange, Listing listing, double quoteBasis, double volumeBasis) {        // final String queryStr = "select m from Market m where exchange=?1 and listing=?2";        try {            return PersistUtil.namedQueryOne(Market.class, "Market.findByMarket", exchange, listing);        } catch (NoResultException e) {            final Market ml = new Market(exchange, listing, quoteBasis, volumeBasis);            PersistUtil.insert(ml);            return ml;        }    }    /**     @return active Markets for the given exchange     */    public static Collection
     
       find(Exchange exchange) {        return PersistUtil.queryList(Market.class, "select s from Market s where exchange=?1 and active=?2", exchange, true);    }    /**     @return active Markets for the given listing     */    public static Collection
      
        find(Listing listing) {        return PersistUtil.queryList(Market.class, "select s from Market s where listing=?1 and active=?2", listing, true);    }    @ManyToOne(optional = false)    public Exchange getExchange() {        return exchange;    }    @ManyToOne(optional = false)    public Listing getListing() {        return listing;    }    @Basic(optional = false)    public double getPriceBasis() {        return listing.getPriceBasis() == 0 ? priceBasis : listing.getPriceBasis();    }    @Transient    public int getScale() {        int length = (int) (Math.log10(getPriceBasis()));        return length;    }    @Basic(optional = false)    public double getVolumeBasis() {        return listing.getVolumeBasis() == 0 ? volumeBasis : listing.getVolumeBasis();    }    /** @return true iff the Listing is currently traded at the Exchange.  The Market could have been retired. */    public boolean isActive() {        return active;    }    @Transient    public Asset getBase() {        return listing.getBase();    }    @Transient    public Asset getQuote() {        return listing.getQuote();    }    @Transient    public int getMargin() {        return listing.getMargin() == 0 ? exchange.getMargin() : listing.getMargin();    }    @Transient    public double getFeeRate() {        return listing.getFeeRate() == 0 ? exchange.getFeeRate() : listing.getFeeRate();    }    @Transient    public FeeMethod getMarginFeeMethod() {        return listing.getMarginFeeMethod() == null ? exchange.getMarginFeeMethod() : listing.getMarginFeeMethod();    }    @Transient    public FeeMethod getFeeMethod() {        return listing.getFeeMethod() == null ? exchange.getFeeMethod() : listing.getFeeMethod();    }    @Transient    public double getMultiplier() {        return listing.getMultiplier();    }    @Transient    public double getTickValue() {        return listing.getTickValue();    }    @Transient    public double getContractSize() {        return listing.getContractSize();    }    @Transient    public double getTickSize() {        return listing.getTickSize();    }    @Transient    public Asset getTradedCurrency() {        return listing.getTradedCurrency();    }    @Transient    public String getSymbol() {        return exchange.toString() + ':' + listing.toString();    }    @Override    public String toString() {        return getSymbol();    }    public static Market forSymbol(String marketSymbol) {        for (Market market : findAll()) {            if (market.getSymbol().equalsIgnoreCase(marketSymbol))                return market;        }        return null;    }    public static List
       
         allSymbols() {        List
        
          result = new ArrayList<>();        List
         
           markets = PersistUtil.queryList(Market.class, "select m from Market m"); for (Market market : markets) result.add((market.getSymbol())); return result; } public static class MarketAmountBuilder { public DiscreteAmount fromPriceCount(long count) { return priceBuilder.fromCount(count); } public DiscreteAmount fromVolumeCount(long count) { return volumeBuilder.fromCount(count); } public DiscreteAmount fromPrice(BigDecimal amount, RemainderHandler remainderHandler) { return priceBuilder.fromValue(amount, remainderHandler); } public DiscreteAmount fromVolume(BigDecimal amount, RemainderHandler remainderHandler) { return volumeBuilder.fromValue(amount, remainderHandler); } public MarketAmountBuilder(double priceBasis, double volumeBasis) { this.priceBuilder = DiscreteAmount.withBasis(priceBasis); this.volumeBuilder = DiscreteAmount.withBasis(volumeBasis); } private final DiscreteAmount.DiscreteAmountBuilder priceBuilder; private final DiscreteAmount.DiscreteAmountBuilder volumeBuilder; } public MarketAmountBuilder buildAmount() { if (marketAmountBuilder == null) marketAmountBuilder = new MarketAmountBuilder(getPriceBasis(), getVolumeBasis()); return marketAmountBuilder; } // JPA protected Market() { } protected void setExchange(Exchange exchange) { this.exchange = exchange; } protected void setListing(Listing listing) { this.listing = listing; } protected void setActive(boolean active) { this.active = active; } protected void setPriceBasis(double quoteBasis) { this.priceBasis = quoteBasis; } protected void setVolumeBasis(double volumeBasis) { this.volumeBasis = volumeBasis; } private Market(Exchange exchange, Listing listing, double priceBasis, double volumeBasis) { this.exchange = exchange; this.listing = listing; this.priceBasis = priceBasis; this.volumeBasis = volumeBasis; this.active = true; } private Exchange exchange;//交易所 private Listing listing;//挂牌清单 private double priceBasis;//基准价格 private double volumeBasis;//基准量 private boolean active;//是否活跃 private MarketAmountBuilder marketAmountBuilder;}