Jackson - best way writes a java list to a json array

Question

I want to use jackson to convert a ArrayList to a JsonArray    Event java   this is the java bean class with two fields  field1    field2  mapped as JsonProperty   My goal is   Convert  ArrayList lt Event gt  list   new ArrayList lt Event gt         list add new Event  a1   a2         list add new Event  b1   b2       To       field1   a1    field   a2      field1   b1    field   b2       The way I can think of is  writeListToJsonArray     public void writeListToJsonArray   throws IOException         ArrayList lt Event gt  list   new ArrayList lt Event gt         list add new Event  a1   a2         list add new Event  b1   b2          OutputStream out   new ByteArrayOutputStream         JsonFactory jfactory   new JsonFactory        JsonGenerator jGenerator   jfactory createJsonGenerator out  JsonEncoding UTF8       ObjectMapper mapper   new ObjectMapper        jGenerator writeStartArray              for  Event event   list            String e   mapper writeValueAsString event           jGenerator writeRaw usage              here  big hassles to write a comma to separate json objects  when the last object in the list is reached  no comma             jGenerator writeEndArray              jGenerator close         System out println out toString         I am looking for something like   generator write out  list      this directly convert the list to json array format and then write it to outputstream  out    even greedier   generator write out  list1   generator write out  list2    this will just convert add in the list1  list2 into a single json array  then write it to  out

User · Answer

In objectMapper we have writeValueAsString   which accepts object as parameter  We can pass object list as parameter get the string back   List lt Apartment gt  aptList    new ArrayList lt Apartment gt         Apartment aptmt   null      for int i 0 i lt 5 i              aptmt  new Apartment             aptmt setAptName  Apartment Name   ArrowHead Ranch             aptmt setAptNum  3153  i            aptmt setPhase  i 1             aptmt setFloorLevel i 2            aptList add aptmt         mapper writeValueAsString aptList

User · Answer

I can t find toByteArray   as  atrioom said  so I use StringWriter  please try   public void writeListToJsonArray   throws IOException            your list     final List lt Event gt  list   new ArrayList lt Event gt  2       list add new Event  a1   a2         list add new Event  b1   b2           final StringWriter sw  new StringWriter        final ObjectMapper mapper   new ObjectMapper        mapper writeValue sw  list       System out println sw toString      use toString   to convert to JSON      sw close         Or just use ObjectMapper writeValueAsString       final ObjectMapper mapper   new ObjectMapper        System out println mapper writeValueAsString list

User · Answer

This is overly complicated  Jackson handles lists via its writer methods just as well as it handles regular objects  This should work just fine for you  assuming I have not misunderstood your question   public void writeListToJsonArray   throws IOException         final List lt Event gt  list   new ArrayList lt Event gt  2       list add new Event  a1   a2         list add new Event  b1   b2          final ByteArrayOutputStream out   new ByteArrayOutputStream        final ObjectMapper mapper   new ObjectMapper         mapper writeValue out  list        final byte   data   out toByteArray        System out println new String data

[java] Jackson - best way writes a java list to a json array

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