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feat: add PrettyFormatInlineArrays option to keep arrays on single line #2972 #3930

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feat: add PrettyFormatInlineArrays option to keep arrays on single line #2972 #3930

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8eecc99
feat: add PrettyFormatInlineArrays feature to keep arrays on single line
sujaykarve111 Jan 3, 2026
2f807d5
refactor: use Context configuration for PrettyFormatInlineArrays inst…
sujaykarve111 Jan 17, 2026
5d952c9
feat: inline short primitive arrays (<5 elements) in pretty-print mode
sujaykarve111 Feb 26, 2026
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21 changes: 21 additions & 0 deletions core/src/main/java/com/alibaba/fastjson2/JSONFactory.java
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Open in desktop
Original file line number Diff line number Diff line change
Expand Up @@ -81,6 +81,7 @@ public static String getProperty(String key) {
static String defaultWriterFormat;
static ZoneId defaultWriterZoneId;
static boolean defaultWriterAlphabetic;
static boolean defaultWriterPrettyFormatInlineArrays;
static boolean defaultSkipTransient;
static final boolean disableReferenceDetect;
static final boolean disableArrayMapping;
Expand Down Expand Up @@ -760,6 +761,26 @@ public static void setDefaultWriterAlphabetic(boolean defaultWriterAlphabetic) {
defaultObjectWriterProvider.setAlphabetic(defaultWriterAlphabetic);
}

/**
* Checks if the default writer uses inline arrays when pretty formatting.
*
* @return true if inline arrays is enabled, false otherwise
* @since 2.0.61
*/
public static boolean isDefaultWriterPrettyFormatInlineArrays() {
return defaultWriterPrettyFormatInlineArrays;
}

/**
* Sets whether the default writer should use inline arrays when pretty formatting.
*
* @param inlineArrays true to enable inline arrays, false to disable
* @since 2.0.61
*/
public static void setDefaultWriterPrettyFormatInlineArrays(boolean inlineArrays) {
JSONFactory.defaultWriterPrettyFormatInlineArrays = inlineArrays;
}

/**
* Checks if reference detection is disabled.
*
Expand Down
62 changes: 62 additions & 0 deletions core/src/main/java/com/alibaba/fastjson2/JSONWriter.java
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Original file line number Diff line number Diff line change
Expand Up @@ -69,6 +69,7 @@ public abstract class JSONWriter
implements Closeable {
static final long WRITE_ARRAY_NULL_MASK = NullAsDefaultValue.mask | WriteNullListAsEmpty.mask;
static final byte PRETTY_NON = 0, PRETTY_TAB = 1, PRETTY_2_SPACE = 2, PRETTY_4_SPACE = 4;
static final int PRETTY_INLINE_ARRAY_MAX_LENGTH = 5;
static final long NONE_DIRECT_FEATURES = ReferenceDetection.mask | NotWriteEmptyArray.mask | NotWriteDefaultValue.mask;

public final Context context;
Expand All @@ -84,12 +85,22 @@ public abstract class JSONWriter

protected boolean startObject;
protected int level;
/**
* Bitmask tracking which nesting levels are arrays (vs objects).
* Bit N is set if level N is an array context.
*/
protected long levelArray;
protected int off;
protected Object rootObject;
protected IdentityHashMap<Object, Path> refs;
protected Path path;
protected String lastReference;
protected byte pretty;
/**
* When true and pretty formatting is enabled, arrays are written inline
* (on a single line) rather than with line breaks between elements.
*/
protected boolean prettyInlineArrays;
protected Object attachment;

protected JSONWriter(
Expand Down Expand Up @@ -119,6 +130,7 @@ protected JSONWriter(
} else {
pretty = PRETTY_NON;
}
prettyInlineArrays = context.prettyFormatInlineArrays;
}

/**
Expand Down Expand Up @@ -1793,6 +1805,10 @@ public void writeInt16(short[] value) {
writeArrayNull();
return;
}
boolean savedInline = prettyInlineArrays;
if (pretty != PRETTY_NON && !prettyInlineArrays && value.length < PRETTY_INLINE_ARRAY_MAX_LENGTH) {
prettyInlineArrays = true;
}
startArray();
for (int i = 0; i < value.length; i++) {
if (i != 0) {
Expand All @@ -1801,6 +1817,7 @@ public void writeInt16(short[] value) {
writeInt16(value[i]);
}
endArray();
prettyInlineArrays = savedInline;
}

/**
Expand Down Expand Up @@ -1968,6 +1985,10 @@ public final void writeFloat(float[] value, DecimalFormat format) {
return;
}

boolean savedInline = prettyInlineArrays;
if (pretty != PRETTY_NON && !prettyInlineArrays && value.length < PRETTY_INLINE_ARRAY_MAX_LENGTH) {
prettyInlineArrays = true;
}
startArray();
for (int i = 0; i < value.length; i++) {
if (i != 0) {
Expand All @@ -1985,6 +2006,7 @@ public final void writeFloat(float[] value, DecimalFormat format) {
writeRaw(str);
}
endArray();
prettyInlineArrays = savedInline;
}

/**
Expand Down Expand Up @@ -2042,11 +2064,16 @@ public final void writeDouble(double value, DecimalFormat format) {
* @param value1 the second double value to write
*/
public void writeDoubleArray(double value0, double value1) {
boolean savedInline = prettyInlineArrays;
if (pretty != PRETTY_NON && !prettyInlineArrays) {
prettyInlineArrays = true;
}
startArray();
writeDouble(value0);
writeComma();
writeDouble(value1);
endArray();
prettyInlineArrays = savedInline;
}

/**
Expand All @@ -2067,6 +2094,10 @@ public final void writeDouble(double[] value, DecimalFormat format) {
return;
}

boolean savedInline = prettyInlineArrays;
if (pretty != PRETTY_NON && !prettyInlineArrays && value.length < PRETTY_INLINE_ARRAY_MAX_LENGTH) {
prettyInlineArrays = true;
}
startArray();
for (int i = 0; i < value.length; i++) {
if (i != 0) {
Expand All @@ -2084,6 +2115,7 @@ public final void writeDouble(double[] value, DecimalFormat format) {
writeRaw(str);
}
endArray();
prettyInlineArrays = savedInline;
}

/**
Expand Down Expand Up @@ -2113,6 +2145,10 @@ public void writeBool(boolean[] value) {
return;
}

boolean savedInline = prettyInlineArrays;
if (pretty != PRETTY_NON && !prettyInlineArrays && value.length < PRETTY_INLINE_ARRAY_MAX_LENGTH) {
prettyInlineArrays = true;
}
startArray();
for (int i = 0; i < value.length; i++) {
if (i != 0) {
Expand All @@ -2121,6 +2157,7 @@ public void writeBool(boolean[] value) {
writeBool(value[i]);
}
endArray();
prettyInlineArrays = savedInline;
}

/**
Expand Down Expand Up @@ -3251,6 +3288,7 @@ public static final class Context {
LabelFilter labelFilter;
ContextValueFilter contextValueFilter;
ContextNameFilter contextNameFilter;
boolean prettyFormatInlineArrays;

/**
* Creates a new Context with the specified object writer provider.
Expand All @@ -3267,6 +3305,7 @@ public Context(ObjectWriterProvider provider) {
this.provider = provider;
this.zoneId = defaultWriterZoneId;
this.maxLevel = defaultMaxLevel;
this.prettyFormatInlineArrays = JSONFactory.defaultWriterPrettyFormatInlineArrays;

String format = defaultWriterFormat;
if (format != null) {
Expand All @@ -3284,6 +3323,7 @@ public Context(Feature... features) {
this.provider = getDefaultObjectWriterProvider();
this.zoneId = defaultWriterZoneId;
this.maxLevel = defaultMaxLevel;
this.prettyFormatInlineArrays = JSONFactory.defaultWriterPrettyFormatInlineArrays;

String format = defaultWriterFormat;
if (format != null) {
Expand All @@ -3306,6 +3346,7 @@ public Context(String format, Feature... features) {
this.provider = getDefaultObjectWriterProvider();
this.zoneId = defaultWriterZoneId;
this.maxLevel = defaultMaxLevel;
this.prettyFormatInlineArrays = JSONFactory.defaultWriterPrettyFormatInlineArrays;

for (int i = 0; i < features.length; i++) {
this.features |= features[i].mask;
Expand Down Expand Up @@ -3335,6 +3376,7 @@ public Context(ObjectWriterProvider provider, Feature... features) {
this.provider = provider;
this.zoneId = defaultWriterZoneId;
this.maxLevel = defaultMaxLevel;
this.prettyFormatInlineArrays = JSONFactory.defaultWriterPrettyFormatInlineArrays;

for (int i = 0; i < features.length; i++) {
this.features |= features[i].mask;
Expand Down Expand Up @@ -3878,6 +3920,26 @@ public int getMaxLevel() {
public void setMaxLevel(int maxLevel) {
this.maxLevel = maxLevel;
}

/**
* Checks if inline arrays is enabled for pretty formatting.
*
* @return true if inline arrays is enabled, false otherwise
* @since 2.0.61
*/
public boolean isPrettyFormatInlineArrays() {
return prettyFormatInlineArrays;
}

/**
* Sets whether to use inline arrays when pretty formatting.
*
* @param prettyFormatInlineArrays true to enable inline arrays, false to disable
* @since 2.0.61
*/
public void setPrettyFormatInlineArrays(boolean prettyFormatInlineArrays) {
this.prettyFormatInlineArrays = prettyFormatInlineArrays;
}
}

public static final long MASK_FIELD_BASED = 1;
Expand Down
74 changes: 71 additions & 3 deletions core/src/main/java/com/alibaba/fastjson2/JSONWriterUTF16.java
View file
Open in desktop
Original file line number Diff line number Diff line change
Expand Up @@ -188,7 +188,11 @@ public final void writeComma() {

chars[off++] = (byte) ',';
if (pretty != PRETTY_NON) {
off = indent(chars, off);
// Check if we're in an array context with inline arrays enabled
boolean inArrayContext = (levelArray & (1L << level)) != 0;
if (!(prettyInlineArrays && inArrayContext)) {
off = indent(chars, off);
}
}
this.off = off;
}
Expand All @@ -198,6 +202,8 @@ public final void startArray() {
if (++level > context.maxLevel) {
overflowLevel();
}
// Mark current level as array context
levelArray |= (1L << level);

int off = this.off;
int minCapacity = off + 3 + pretty * level;
Expand All @@ -207,14 +213,16 @@ public final void startArray() {
}

chars[off++] = (byte) '[';
if (pretty != PRETTY_NON) {
if (pretty != PRETTY_NON && !prettyInlineArrays) {
off = indent(chars, off);
}
this.off = off;
}

@Override
public final void endArray() {
// Clear array context for current level before decrementing
levelArray &= ~(1L << level);
level--;
int off = this.off;
int minCapacity = off + 1 + (pretty == 0 ? 0 : pretty * level + 1);
Expand All @@ -223,7 +231,7 @@ public final void endArray() {
chars = grow(minCapacity);
}

if (pretty != PRETTY_NON) {
if (pretty != PRETTY_NON && !prettyInlineArrays) {
off = indent(chars, off);
}
chars[off] = (byte) ']';
Expand Down Expand Up @@ -1747,6 +1755,18 @@ public final void writeInt32(int[] value) {
return;
}

if (pretty != PRETTY_NON && !prettyInlineArrays && value.length >= PRETTY_INLINE_ARRAY_MAX_LENGTH) {
startArray();
for (int i = 0; i < value.length; i++) {
if (i != 0) {
writeComma();
}
writeInt32(value[i]);
}
endArray();
return;
}

boolean writeAsString = (context.features & WriteNonStringValueAsString.mask) != 0;

int off = this.off;
Expand Down Expand Up @@ -1802,6 +1822,18 @@ public final void writeInt8(byte[] value) {
return;
}

if (pretty != PRETTY_NON && !prettyInlineArrays && value.length >= PRETTY_INLINE_ARRAY_MAX_LENGTH) {
startArray();
for (int i = 0; i < value.length; i++) {
if (i != 0) {
writeComma();
}
writeInt8(value[i]);
}
endArray();
return;
}

boolean writeAsString = (context.features & WriteNonStringValueAsString.mask) != 0;

int off = this.off;
Expand Down Expand Up @@ -1888,6 +1920,18 @@ public final void writeInt64(long[] values) {
return;
}

if (pretty != PRETTY_NON && !prettyInlineArrays && values.length >= PRETTY_INLINE_ARRAY_MAX_LENGTH) {
startArray();
for (int i = 0; i < values.length; i++) {
if (i != 0) {
writeComma();
}
writeInt64(values[i]);
}
endArray();
return;
}

int off = this.off;
int minCapacity = off + 2 + values.length * 23;
char[] chars = this.chars;
Expand Down Expand Up @@ -2081,6 +2125,18 @@ public final void writeFloat(float[] values) {
return;
}

if (pretty != PRETTY_NON && !prettyInlineArrays && values.length >= PRETTY_INLINE_ARRAY_MAX_LENGTH) {
startArray();
for (int i = 0; i < values.length; i++) {
if (i != 0) {
writeComma();
}
writeFloat(values[i]);
}
endArray();
return;
}

boolean writeAsString = (context.features & WriteNonStringValueAsString.mask) != 0;
boolean writeSpecialAsString = (context.features & WriteFloatSpecialAsString.mask) != 0;

Expand Down Expand Up @@ -2200,6 +2256,18 @@ public final void writeDouble(double[] values) {
return;
}

if (pretty != PRETTY_NON && !prettyInlineArrays && values.length >= PRETTY_INLINE_ARRAY_MAX_LENGTH) {
startArray();
for (int i = 0; i < values.length; i++) {
if (i != 0) {
writeComma();
}
writeDouble(values[i]);
}
endArray();
return;
}

boolean writeAsString = (context.features & WriteNonStringValueAsString.mask) != 0;
boolean writeSpecialAsString = (context.features & WriteFloatSpecialAsString.mask) != 0;

Expand Down
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