将JSON反序列化以映射[String，SomeJavaObject]与Spring、Scala和Jackson

Question

我刚刚开始尝试Scala，并尝试在现有的Java/Spring应用程序中使用Jackson2.3.1和Jackson-module-scala。

我试图将JSON反序列化，如下面所示，以字符串到颜色对象的映射结束，但当我运行下面的代码时，我以字符串到映射结束：

{
  "1A-X": {
    "c": 0,
    "m": 0,
    "y": 0,
    "k": 0,
    "r": 255,
    "g": 255,
    "b": 255
  }
}

为什么结果地图的值是另一个地图而不是颜色对象？

Color是一个具有@JSONCreator注释构造函数的现有Java类。

@RequestMapping(Array("/swatches"))
def setSwatches(@RequestBody swatches: Map[String, Color]) = {
  println(swatches)
  println("Map class " + swatches.getClass + ", key class " + swatches.get("1A-X").get.getClass)
}

将上述JSON传递给这段代码的输出如下：

Map(1A-X -> Map(y -> 1, m -> 1, b -> 51, g -> 1, c -> 1, r -> 5, k -> 1))
Map class class scala.collection.immutable.Map$Map1, key class class scala.collection.immutable.HashMap$HashTrieMap

import com.fasterxml.jackson.annotation.JsonCreator;
import com.fasterxml.jackson.annotation.JsonIgnore;
import com.fasterxml.jackson.annotation.JsonProperty;
import com.google.common.base.Preconditions;

public final class Color {
  static final Color NOCOLOR = new Color(0f, 0f, 0f, -1f, -1, -1, -1);
  private final float c, m, y, k;
  private final int   r, g, b;

  /** from string in format: CMYKcolor(0,0,0,0) or CMYKRGBcolor(c,m,y,k,r,g,b)*/
  static Color valueOf(final String colorStringFormat) {
    return colorStringFormat == null || colorStringFormat.isEmpty()
    ? NOCOLOR : new Color(colorStringFormat);
  }

  /** from string in format: CMYKcolor(0,0,0,0) CMYKRGBcolor(c,m,y,k,r,g,b)*/
  Color(final String colorStringFormat) {
    this(colorStringFormat.substring(colorStringFormat.indexOf('(') + 1,
      colorStringFormat.indexOf(')')).split(","));
  }

  Color(final String... colors) {
    this(Float.parseFloat(colors[0]), Float.parseFloat(colors[1]),
      Float.parseFloat(colors[2]), Float.parseFloat(colors[3]),
      (colors.length==4)?-1:Integer.parseInt(colors[4]), 
        (colors.length==4)?-1:Integer.parseInt(colors[5]),
          (colors.length==4)?-1:Integer.parseInt(colors[6])); 
  }

  /** all values must be between 0f and 1f inclusive */
  public Color(final float c, final float m, final float y, final float k) {
    this(c, m, y, k, -1, -1, -1);
  }

  /** cmyk values must be between 0f and 1f inclusive; rgb values must be between 0 and 255 inclusive */
  @JsonCreator
  public Color(@JsonProperty("c") final float c, @JsonProperty("m") final float m, @JsonProperty("y") final float y,
    @JsonProperty("k") final float k, @JsonProperty("r") final int r, @JsonProperty("g") final int g,
    @JsonProperty("b") final int b) {
    Preconditions.checkArgument(isValidCMYKValue(c, m, y, k),
      "CMYK values must be a float value between 0 and 1 inclusive. " +
      "Was (%s, %s, %s, %s).", c, m, y, k);
    Preconditions.checkArgument(isValidRGBValue(r, g, b),
      "RBG values must be an int value between 0 and 255 inclusive " +
      "or -1 to indicate no value. Was (%s, %s, %s).", r, g, b);
    this.c = c;
    this.m = m;
    this.y = y;
    this.k = k;
    this.r = r;
    this.g = g;
    this.b = b;                     
  }

  private static boolean isValidCMYKValue(final float c, final float m, final float y, final float k) {
    return
    c >= 0f && c <= 1f &&
    m >= 0f && m <= 1f &&
    y >= 0f && y <= 1f &&
    (k >= 0f && k <= 1f) || k == -1;
  }

  private static boolean isValidRGBValue(final int r, final int g, final int b) {
    return (r >= 0 && r <= 255 && g >= 0 && g <= 255 && b >= 0 && b <= 255)
    || (r == -1 && g == -1 && b == -1);
  }

  public float getC() { return c; }
  public float getM() { return m; }
  public float getY() { return y; }
  public float getK() { return k; }
  public int   getR() { return r; }
  public int   getG() { return g; }
  public int   getB() { return b; }

  @JsonIgnore
  public boolean isRGBAlternatePresent() {
    return r > -1;
  }

  public boolean isPresent() {
    return k > -1;
  }

}

{
  "c": 0,
  "m": 0,
  "y": 0,
  "k": 0,
  "r": 255,
  "g": 255,
  "b": 255
}

Answer 1

这个问题的根本原因似乎不是Scala特有的，尽管Scala模块目前不支持解决这个问题的方法。

关于这个主题的另一个问题表明，当反序列化泛型类型时，Spring没有向Jackson提供完全指定的类型信息；Spring实际上是在告诉Jackson反序列化映射[_,_]。

使用jackson将JSON对象数组映射到@RequestBody列表

class ColorMap extends java.util.HashMap[String,Color]
@RequestMapping(Array("/swatches"))
def setSwatches(@RequestBody swatches: ColorMap) = ...

在Scala模块实现奇偶校验之前，或者在Spring纠正其类型传播之前，您将需要使用Java集合的派生类，如上所述。