protobuf 负载比 JSON 大？

Question

我有一个“级别”对象列表的对象，我正在测试用 Spring Boot Rest Controller 以两种方式传输它们：

1. 使用 JSON，在 Rest Controller 中我使用类似：

    @RequestMapping(value = "/api/v1/layers/{layername}", method =         RequestMethod.GET, produces = "application/json")
    public @ResponseBody List<Level>  query(@PathVariable String layername,
                  @RequestParam("northEastLat") Float northEastLat,
                  @RequestParam("northEastLng") Float northEastLng,
                  @RequestParam("northWestLat") Float northWestLat,
                  @RequestParam("northWestLng") Float northWestLng,
   
                  @RequestParam("southEastLat") Float southEastLat,
                  @RequestParam("southEastLng") Float southEastLng,
                  @RequestParam("southWestLat") Float southWestLat,
                  @RequestParam("southWestLng") Float southWestLng
   ) {
   
   List<Level> poligons=levelService.obtainLevels(layername,southWestLng,southWestLat,northWestLng,northWestLat,northEastLng,northEastLat,southEastLng,southEastLat);
   int i=1;
   for (Level p : poligons) {
   
       System.out.println("poligon" + i++ + " is:" + p.toString());
   }
   
   return poligons;
   }
   

2. 对于 Protostuff Protobuf 格式，我使用类似：

     @RequestMapping(value = "/api/v1/layers/{layername}", method = RequestMethod.GET,produces = "text/plain")
     public String query(@PathVariable String layername,
                   @RequestParam("northEastLat") Float northEastLat,
                   @RequestParam("northEastLng") Float northEastLng,
                   @RequestParam("northWestLat") Float northWestLat,
                   @RequestParam("northWestLng") Float northWestLng,
   
                   @RequestParam("southEastLat") Float southEastLat,
                   @RequestParam("southEastLng") Float southEastLng,
                   @RequestParam("southWestLat") Float southWestLat,
                   @RequestParam("southWestLng") Float southWestLng
     ) {
   
   
   List<Level> poligons=levelService.obtainLevels(layername,southWestLng,southWestLat,northWestLng,northWestLat,northEastLng,northEastLat,southEastLng,southEastLat);
   LevelList list = new LevelList(poligons);
   
   byte[] bytes;
   
   int i=1;
   for (Level p : poligons) {
   
       System.out.println("poligon" + i++ + " is:" + p.toString());
   }
   
   Schema<LevelList> schema = RuntimeSchema.getSchema(LevelList.class);
   LinkedBuffer buffer = LinkedBuffer.allocate();
   
   
   
   try
   {
       bytes = ProtostuffIOUtil.toByteArray(list, schema, buffer);
   }
   finally
   {
       buffer.clear();
   }
   
    return new String(bytes);
   }
   

关卡对象格式为： [{"wkb_geometry":"{"type":"Polygon","coordinates":[[[24.446822,45.34997],[24.706508,45.352485]]]}","id":199,"level":"3 ","type":null}

关卡对象是：

@Entity(name = "Level")
@Table(name="Level2G")
@SecondaryTables({
    @SecondaryTable(name="Level3G"),
    @SecondaryTable(name="Level4G")
})
public class Level implements Serializable {

private static final long serialVersionUID = 1L;

// @Column(name = "wkb_geometry",columnDefinition="Geometry")
//@Type(type = "org.hibernate.spatial.GeometryType")
@Column(name="wkb_geometry")
private /*Geometry */ String  wkb_geometry;

@Id
@Column(name="id")
private Integer id;


@Column(name="level")
private String level;

@Transient
private String type;

public Level() {
}

public Level(String  wkb_geometry, Integer id, String level) {
    this.wkb_geometry = wkb_geometry;
    this.id = id;
    this.level = level;
    this.type = "Feature";
}

public Level(String  wkb_geometry, Integer id, String level, String type) {
    this.wkb_geometry = wkb_geometry;
    this.id = id;
    this.level = level;
    this.type = type;
}

public Object getWkb_geometry() {
    return wkb_geometry;
}

public void setWkb_geometry(String  wkb_geometry) {
    this.wkb_geometry = wkb_geometry;
}

public Integer getId() {
    return id;
}

public void setId(Integer id) {
    this.id = id;
}

public String getLevel() {
    return level;
}

public void setLevel(String level) {
    this.level = level;
}

public String getType() {
    return type;
}

public void setType(String type) {
    this.type = type;
}

@Override
public String toString() {
    return "Level{" +
            "wkb_geometry=" + wkb_geometry +
            ", id=" + id +
            ", level='" + level + '\'' +
            ", type='" + type + '\'' +
            '}';
}
 }

LevelList 对象只是关卡对象的列表

问题在于，与 JSON (3.7kb) 相比，使用 Protostuff 可以获得更大的有效负载 (26kb)。为什么？

对于第二个选项，我还尝试将“application/octet-stream”设置为直接返回字节，但结果仍然相同。我还比较了 JSON 和 protobuf 的速度；即使负载更大，protobuf 也具有更好的性能。知道为什么吗？

Answer 1

Protostuff 和 Protobuf 不是一回事。 Protostuff 是一个包装库，可以使用许多不同的序列化格式。它还支持您似乎正在使用的运行时模式生成。该运行时模式需要与消息一起发送额外的元数据，以告知接收者消息的模式。我猜你看到的大消息主要来自这个运行时模式数据。

使用标准 Protobuf，模式不会随消息一起发送，因为假定发送者和接收者已经就编译到两个程序中的 .proto 文件提供的模式达成一致。如果您将 Protobuf 与标准 .proto 文件一起使用，您会发现它生成的消息比 JSON 小得多。

Answer 2

你的测试中至少有一个问题。

从字节数组到字符串的这种转换是无效的：

bytes = ProtostuffIOUtil.toByteArray(list, schema, buffer);
return new String(bytes);

String 的此构造函数将尝试将字节数组解析为 UTF-8 字符串（很可能；取决于您的语言环境设置），但根据定义给定的数据不是有效的 UTF-8 字符串。

如果你想进行更好的尺寸比较，你应该写一个如下形式的测试：

LevelList source = testData();
byte[] jsonData = generateJson(source);
byte[] protobufData = generateProtobuf(source);
System.out.println("JSON=" + jsonData.size() + " Protobuf=" + protobufData.size());

这里的重点是使您的测试可重复，以便其他人可以重复它。