java jackson examples

user.json文件数据如下：

{
  "name" : { "first" : "Joe", "last" : "Sixpack" },
  "gender" : "MALE",
  "verified" : false,
  "userImage" : "Rm9vYmFyIQ=="
}

User.java

public class User {
    public enum Gender { MALE, FEMALE };

    public static class Name {
      private String _first, _last;

      public String getFirst() { return _first; }
      public String getLast() { return _last; }

      public void setFirst(String s) { _first = s; }
      public void setLast(String s) { _last = s; }
    }

    private Gender _gender;
    private Name _name;
    private boolean _isVerified;
    private byte[] _userImage;

    public Name getName() { return _name; }
    public boolean isVerified() { return _isVerified; }
    public Gender getGender() { return _gender; }
    public byte[] getUserImage() { return _userImage; }

    public void setName(Name n) { _name = n; }
    public void setVerified(boolean b) { _isVerified = b; }
    public void setGender(Gender g) { _gender = g; }
    public void setUserImage(byte[] b) { _userImage = b; }
}

将json转换为User对象

ObjectMapper mapper = new ObjectMapper(); // can reuse, share globally
User user = mapper.readValue(new File("user.json"), User.class);

将json转换为Map对象

Map<String,Object> userData = mapper.readValue(new File("user.json"), Map.class);

通过向Map中添加数据来生成json

Map<String,Object> userData = new HashMap<String,Object>();
Map<String,String> nameStruct = new HashMap<String,String>();
nameStruct.put("first", "Joe");
nameStruct.put("last", "Sixpack");
userData.put("name", nameStruct);
userData.put("gender", "MALE");
userData.put("verified", Boolean.FALSE);
userData.put("userImage", "Rm9vYmFyIQ==");

mapper.writeValue(new File("user-modified.json"), userData);

类型对照：

Map<String,User> result = mapper.readValue(src, new TypeReference<Map<String,User>>() { });

ObjectMapper m = new ObjectMapper();
// can either use mapper.readTree(JsonParser), or bind to JsonNode
JsonNode rootNode = m.readValue(new File("user.json"), JsonNode.class);
// ensure that "last name" isn't "Xmler"; if is, change to "Jsoner"
JsonNode nameNode = rootNode.path("name");
String lastName = nameNode.path("last").getTextValue().
if ("xmler".equalsIgnoreCase(lastName)) {
  ((ObjectNode)nameNode).put("last", "Jsoner");
}
// and write it out:
m.writeValue(new File("user-modified.json"), rootNode);

TreeMapper treeMapper = new TreeMapper();
ObjectNode userOb = treeMapper.objectNode();
Object nameOb = userRoot.putObject("name");
nameOb.put("first", "Joe");
nameOb.put("last", "Sixpack");
userOb.put("gender", User.Gender.MALE.toString());
userOb.put("verified", false);
byte[] imageData = getImageData(); // or wherever it comes from
userOb.put("userImage", imageData);

JsonFactory f = new JsonFactory();
JsonGenerator g = f.createJsonGenerator(new File("user.json"));
g.writeStartObject();
g.writeObjectFieldStart("name");
g.writeStringField("first", "Joe");
g.writeStringField("last", "Sixpack");
g.writeEndObject(); // for field 'name'
g.writeStringField("gender", Gender.MALE);
g.writeBooleanField("verified", false);
g.writeFieldName("userImage"); // no 'writeBinaryField' (yet?)
byte[] binaryData = ...;
g.writeBinary(binaryData);
g.writeEndObject();
g.close(); // important: will force flushing of output, close underlying output stream

JsonFactory f = new JsonFactory();
JsonParser jp = f.createJsonParser(new File("user.json"));
User user = new User();
jp.nextToken(); // will return JsonToken.START_OBJECT (verify?)
while (jp.nextToken() != JsonToken.END_OBJECT) {
  String fieldname = jp.getCurrentName();
  jp.nextToken(); // move to value, or START_OBJECT/START_ARRAY
  if ("name".equals(fieldname)) { // contains an object
    Name name = new Name();
    while (jp.nextToken() != JsonToken.END_OBJECT) {
      String namefield = jp.getCurrentName();
      jp.nextToken(); // move to value
      if ("first".equals(namefield)) {
        name.setFirst(jp.getText());
      } else if ("last".equals(namefield)) {
        name.setLast(jp.getText());
      } else {
        throw new IllegalStateException("Unrecognized field '"+fieldname+"'!");
      }
    }
    user.setName(name);
  } else if ("gender".equals(fieldname)) {
    user.setGender(Gender.valueOf(jp.getText()));
  } else if ("verified".equals(fieldname)) {
    user.setVerified(jp.getCurrentToken() == JsonToken.VALUE_TRUE);
  } else if ("userImage".equals(fieldname)) {
    user.setUserImage(jp.getBinaryValue());
  } else {
    throw new IllegalStateException("Unrecognized field '"+fieldname+"'!");
  }
}
jp.close(); // ensure resources get cleaned up timely and properly