Android Json的使用（2） 使用Jackson解析和生成json

使用Jackson的三种方式

数据绑定模式：使用最方便

流模式：性能最佳

树模式：最灵活

以最常用的数据绑定模式为例

Json数据如下

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{

"name" : { "first" : "Joe", "last" : "Sixpack" },

"gender" : "MALE",

"verified" : false,

"userImage" : "Rm9vYmFyIQ=="

}

json生成具体的java对象实例

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ObjectMapper mapper = new ObjectMapper(); // can reuse, share globally

User user = mapper.readValue(new File("user.json"), User.class);

下面是User类：

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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; }

从Java对象转换成Json

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

树模式例子

你还有另外一种方式来使用Jackson，就是使用树模式。这个就像XML的DOM树。Jackson用JsonNode来生成树。

如下所示：

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ObjectMapper m = new ObjectMapper();

// can either use mapper.readTree(source), or mapper.readValue(source, JsonNode.class);

JsonNode rootNode = m.readTree(new File("user.json"));

// 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);

你也可以自己构造一个树：

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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);

流模式

这是最高效的模式。

生成json文本

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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

解析Json

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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(User.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

详细内容参见：http://wiki.fasterxml.com/JacksonInFiveMinutes

使用Jackson的三种方式

数据绑定模式：使用最方便

流模式：性能最佳

树模式：最灵活

以最常用的数据绑定模式为例

Json数据如下

[plain] view plain copy

{

"name" : { "first" : "Joe", "last" : "Sixpack" },

"gender" : "MALE",

"verified" : false,

"userImage" : "Rm9vYmFyIQ=="

}

json生成具体的java对象实例

[java] view plain copy

ObjectMapper mapper = new ObjectMapper(); // can reuse, share globally

User user = mapper.readValue(new File("user.json"), User.class);

下面是User类：

[java] view plain copy

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; }

从Java对象转换成Json

[java] view plain copy

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

树模式例子

你还有另外一种方式来使用Jackson，就是使用树模式。这个就像XML的DOM树。Jackson用JsonNode来生成树。

如下所示：

[java] view plain copy

ObjectMapper m = new ObjectMapper();

// can either use mapper.readTree(source), or mapper.readValue(source, JsonNode.class);

JsonNode rootNode = m.readTree(new File("user.json"));

// 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);

你也可以自己构造一个树：

[java] view plain copy

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);

流模式

这是最高效的模式。

生成json文本

[java] view plain copy

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

解析Json

[java] view plain copy

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(User.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

详细内容参见：http://wiki.fasterxml.com/JacksonInFiveMinutes