相信在SpringBoot的开发中，很多都有遇到过返回的对象中存在NULL或者空值的字段，如下图所示：
对于这种情况，需要将空值字段去掉，那么解决方法如下：
使用SpringBoot中的注解：@JsonInclude，我们只需要在过滤的字段或者实体类上面加上
如下注解即可
@JsonInclude(JsonInclude.Include.ALWAYS.NON_NULL)
！注意 ！！注意 ！
注解参数选择
- 将该注解放在属性上，如果该属性为NULL则不参与序列化；
- 如果放在类上边,那对这个类的全部属性起作用；
- JsonInclude.Include.ALWAYS --默认，所有的属性都会被序列化
- JsonInclude.Include.NON_DEFAULT --属性为默认值不序列化
- JsonInclude.Include.NON_EMPTY --属性为空（""）或者为 NULL 都不序列化
- JsonInclude.Include.NON_NULL --属性为NULL 不序列化
- JsonInclude.Include.CUSTOM --这个是自定义包含规则，详细见官方文档
- JsonInclude.Include.NON_ABSENT --这个包含NON_NULL，即为null的时候不序列化，详情看源码
- JsonInclude.Include.USE_DEFAULTS --使用默认值的情况下就不序列化
下面附上源码：
JsonInclude类
//
// Source code recreated from a .class file by IntelliJ IDEA
// (powered by FernFlower decompiler)
//
package com.fasterxml.jackson.annotation;
import java.io.Serializable;
import java.lang.annotation.ElementType;
import java.lang.annotation.Retention;
import java.lang.annotation.RetentionPolicy;
import java.lang.annotation.Target;
@Target({ElementType.ANNOTATION_TYPE, ElementType.METHOD, ElementType.FIELD, ElementType.TYPE, ElementType.PARAMETER})
@Retention(RetentionPolicy.RUNTIME)
@JacksonAnnotation
public @interface JsonInclude {
JsonInclude.Include value() default JsonInclude.Include.ALWAYS;
JsonInclude.Include content() default JsonInclude.Include.ALWAYS;
Class<?> valueFilter() default Void.class;
Class<?> contentFilter() default Void.class;
public static class Value implements JacksonAnnotationValue<JsonInclude>, Serializable {
private static final long serialVersionUID = 1L;
protected static final JsonInclude.Value EMPTY;
protected final JsonInclude.Include _valueInclusion;
protected final JsonInclude.Include _contentInclusion;
protected final Class<?> _valueFilter;
protected final Class<?> _contentFilter;
public Value(JsonInclude src) {
this(src.value(), src.content(), src.valueFilter(), src.contentFilter());
}
protected Value(JsonInclude.Include vi, JsonInclude.Include ci, Class<?> valueFilter, Class<?> contentFilter) {
this._valueInclusion = vi == null ? JsonInclude.Include.USE_DEFAULTS : vi;
this._contentInclusion = ci == null ? JsonInclude.Include.USE_DEFAULTS : ci;
this._valueFilter = valueFilter == Void.class ? null : valueFilter;
this._contentFilter = contentFilter == Void.class ? null : contentFilter;
}
public static JsonInclude.Value empty() {
return EMPTY;
}
public static JsonInclude.Value merge(JsonInclude.Value base, JsonInclude.Value overrides) {
return base == null ? overrides : base.withOverrides(overrides);
}
public static JsonInclude.Value mergeAll(JsonInclude.Value... values) {
JsonInclude.Value result = null;
JsonInclude.Value[] var2 = values;
int var3 = values.length;
for(int var4 = 0; var4 < var3; ++var4) {
JsonInclude.Value curr = var2[var4];
if (curr != null) {
result = result == null ? curr : result.withOverrides(curr);
}
}
return result;
}
protected Object readResolve() {
return this._valueInclusion == JsonInclude.Include.USE_DEFAULTS && this._contentInclusion == JsonInclude.Include.USE_DEFAULTS && this._valueFilter == null && this._contentFilter == null ? EMPTY : this;
}
public JsonInclude.Value withOverrides(JsonInclude.Value overrides) {
if (overrides != null && overrides != EMPTY) {
JsonInclude.Include vi = overrides._valueInclusion;
JsonInclude.Include ci = overrides._contentInclusion;
Class<?> vf = overrides._valueFilter;
Class<?> cf = overrides._contentFilter;
boolean viDiff = vi != this._valueInclusion && vi != JsonInclude.Include.USE_DEFAULTS;
boolean ciDiff = ci != this._contentInclusion && ci != JsonInclude.Include.USE_DEFAULTS;
boolean filterDiff = vf != this._valueFilter || cf != this._valueFilter;
if (viDiff) {
return ciDiff ? new JsonInclude.Value(vi, ci, vf, cf) : new JsonInclude.Value(vi, this._contentInclusion, vf, cf);
} else if (ciDiff) {
return new JsonInclude.Value(this._valueInclusion, ci, vf, cf);
} else {
return filterDiff ? new JsonInclude.Value(this._valueInclusion, this._contentInclusion, vf, cf) : this;
}
} else {
return this;
}
}
public static JsonInclude.Value construct(JsonInclude.Include valueIncl, JsonInclude.Include contentIncl) {
return valueIncl != JsonInclude.Include.USE_DEFAULTS && valueIncl != null || contentIncl != JsonInclude.Include.USE_DEFAULTS && contentIncl != null ? new JsonInclude.Value(valueIncl, contentIncl, (Class)null, (Class)null) : EMPTY;
}
public static JsonInclude.Value construct(JsonInclude.Include valueIncl, JsonInclude.Include contentIncl, Class<?> valueFilter, Class<?> contentFilter) {
if (valueFilter == Void.class) {
valueFilter = null;
}
if (contentFilter == Void.class) {
contentFilter = null;
}
return (valueIncl == JsonInclude.Include.USE_DEFAULTS || valueIncl == null) && (contentIncl == JsonInclude.Include.USE_DEFAULTS || contentIncl == null) && valueFilter == null && contentFilter == null ? EMPTY : new JsonInclude.Value(valueIncl, contentIncl, valueFilter, contentFilter);
}
public static JsonInclude.Value from(JsonInclude src) {
if (src == null) {
return EMPTY;
} else {
JsonInclude.Include vi = src.value();
JsonInclude.Include ci = src.content();
if (vi == JsonInclude.Include.USE_DEFAULTS && ci == JsonInclude.Include.USE_DEFAULTS) {
return EMPTY;
} else {
Class<?> vf = src.valueFilter();
if (vf == Void.class) {
vf = null;
}
Class<?> cf = src.contentFilter();
if (cf == Void.class) {
cf = null;
}
return new JsonInclude.Value(vi, ci, vf, cf);
}
}
}
public JsonInclude.Value withValueInclusion(JsonInclude.Include incl) {
return incl == this._valueInclusion ? this : new JsonInclude.Value(incl, this._contentInclusion, this._valueFilter, this._contentFilter);
}
public JsonInclude.Value withValueFilter(Class<?> filter) {
JsonInclude.Include incl;
if (filter != null && filter != Void.class) {
incl = JsonInclude.Include.CUSTOM;
} else {
incl = JsonInclude.Include.USE_DEFAULTS;
filter = null;
}
return construct(incl, this._contentInclusion, filter, this._contentFilter);
}
public JsonInclude.Value withContentFilter(Class<?> filter) {
JsonInclude.Include incl;
if (filter != null && filter != Void.class) {
incl = JsonInclude.Include.CUSTOM;
} else {
incl = JsonInclude.Include.USE_DEFAULTS;
filter = null;
}
return construct(this._valueInclusion, incl, this._valueFilter, filter);
}
public JsonInclude.Value withContentInclusion(JsonInclude.Include incl) {
return incl == this._contentInclusion ? this : new JsonInclude.Value(this._valueInclusion, incl, this._valueFilter, this._contentFilter);
}
public Class<JsonInclude> valueFor() {
return JsonInclude.class;
}
public JsonInclude.Include getValueInclusion() {
return this._valueInclusion;
}
public JsonInclude.Include getContentInclusion() {
return this._contentInclusion;
}
public Class<?> getValueFilter() {
return this._valueFilter;
}
public Class<?> getContentFilter() {
return this._contentFilter;
}
public String toString() {
StringBuilder sb = new StringBuilder(80);
sb.append("JsonInclude.Value(value=").append(this._valueInclusion).append(",content=").append(this._contentInclusion);
if (this._valueFilter != null) {
sb.append(",valueFilter=").append(this._valueFilter.getName()).append(".class");
}
if (this._contentFilter != null) {
sb.append(",contentFilter=").append(this._contentFilter.getName()).append(".class");
}
return sb.append(')').toString();
}
public int hashCode() {
return (this._valueInclusion.hashCode() << 2) + this._contentInclusion.hashCode();
}
public boolean equals(Object o) {
if (o == this) {
return true;
} else if (o == null) {
return false;
} else if (o.getClass() != this.getClass()) {
return false;
} else {
JsonInclude.Value other = (JsonInclude.Value)o;
return other._valueInclusion == this._valueInclusion && other._contentInclusion == this._contentInclusion && other._valueFilter == this._valueFilter && other._contentFilter == this._contentFilter;
}
}
static {
EMPTY = new JsonInclude.Value(JsonInclude.Include.USE_DEFAULTS, JsonInclude.Include.USE_DEFAULTS, (Class)null, (Class)null);
}
}
public static enum Include {
ALWAYS,
NON_NULL,
NON_ABSENT,
NON_EMPTY,
NON_DEFAULT,
CUSTOM,
USE_DEFAULTS;
private Include() {
}
}
}