java protobuf负载比JSON大？

1 周，3 日 Questions & Answers 1080

我有一个对象，它是一个“级别”对象列表，我正在用Spring Boot Rest Controller以两种方式测试传输它们：

对于JSON，我在Rest控制器中使用如下内容：

 @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;
}

对于Protostuff Protobuf格式，我使用如下内容：

  @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);
}

级别对象格式为： [{“wkb_几何”：“{”类型“：”多边形“，”坐标“：[[[24.446822,45.34997]，[24.706508,45.352485]]}”，“id”：199，“级别”：“3”，“类型”：null}

级别对象是：

@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对象只是级别对象的列表

问题是，与JSON（3.7kb）相比，Protostuff的有效负载（26KB）更大。为什么?

同样对于第二个选项，我也尝试设置“application/octetstream”直接返回字节，但结果仍然相同。我还比较了JSON和protobuf的速度；protobuf即使在负载更大的情况下也具有更好的性能。知道为什么吗

共 (2) 个答案

# 1 楼答案

Protostuff和Protobuf不是一回事。Protostuff是一个包装器库，可以使用多种不同的序列化格式。它还支持运行时模式生成，您似乎正在使用它。该运行时模式需要随消息一起发送额外的元数据，以告知接收方消息的模式。我猜您看到的大消息主要来自此运行时模式数据

使用标准Protobuf，模式不会与消息一起发送，因为假定发送方和接收方已经同意由编译到两个程序中的.proto文件提供的模式。如果将Protobuf与标准的.proto文件一起使用，您会发现它生成的消息比JSON小得多
# 2 楼答案
您的测试中至少有一个问题

从字节数组到字符串的转换无效：
```
bytes = ProtostuffIOUtil.toByteArray(list, schema, buffer);
return new String(bytes);
```
此字符串构造函数将尝试将字节数组解析为UTF-8字符串（很可能，这取决于您的语言环境设置），但根据定义提供的数据不是有效的UTF-8字符串

如果要进行更好的大小比较，应按以下形式编写测试：
```
LevelList source = testData();
byte[] jsonData = generateJson(source);
byte[] protobufData = generateProtobuf(source);
System.out.println("JSON=" + jsonData.size() + " Protobuf=" + protobufData.size());
```
这里的要点是使您的测试具有可复制性，以便其他人可以重复它

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java protobuf负载比JSON大？

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