我有一个非常复杂的Json对象，我得到一个字符串：
{ "a": ..., "b":..., /* lots of other properties */ "z":... }
我与杰克逊部分阅读并映射到Java类：
class PartialObjectForB { @JsonProperty("b") private ObjectB b; }
我使用ObjectMapper类中的readValue（）方法得到我想要的东西......到目前为止，非常好。
现在，我想更新PartialObjectForB中的一些值并更新我的初始字符串。 我想到了如何使用jackson更新Java对象（通过使用readerForUpdating），但无法找到相反的方法：用Java对象更新Json对象/字符串。
我知道如何使用JSONObject快速解决该问题。例如，如果我只想更新1个值：
JSONObject j = new JSONObject(/* the full json string */);
j.getJSONObject("b").getJSONObject("bb")/* etc. */.put("bbbb", 4);
j.toString(); // will give me the full original text with only "b" updated.
但是杰克逊找不到怎么做。
有什么想法吗？
注意：
答案 0 :(得分：2)
胜利！ :)我现在有一个实现它并不是很简单。 基准杰克逊与JSONObject包括在内。
问题和解决方案逐件描述：
首先，我在数据存储中有一个大的json字符串，我想要部分反序列化和更新。反序列化必须是部分的，但序列化完整，所以我不会丢失我没有反序列化的数据。 以下是我用于示例的对象：
private static class KnownPart {
@JsonProperty
private Customer customer;
@JsonProperty
private BrowserInfo browser;
}
private static class Customer {
@JsonProperty
private int id;
@JsonProperty
private String name;
@JsonProperty
private Address[] addresses; // just to make it more complex for this example
public Customer(int id, String name, Address[] addresses) {
this.id = id;
this.name = name;
this.addresses = addresses;
}
public Customer() {
}
}
private static class Address {
@JsonProperty
private String street;
@JsonProperty
private String city;
public Address(String street, String city) {
this.street = street;
this.city = city;
}
public Address() {
}
}
private static class BrowserInfo {
@JsonProperty
private String agent;
@JsonProperty
private String version;
public BrowserInfo(String agent, String version) {
this.agent = agent;
this.version = version;
}
public BrowserInfo() {
}
}
KnownPart对象包含2个以上的属性，但我完全不知道哪些属性，我不能保证跟踪哪些属性被添加到json字符串...
我有一个数据存储，其数据以Json编码。当前实现使用JSONObject进行读/写，并支持jackson读取json并将其映射到“真实”Java对象（POJO和更复杂的对象）。 虽然使用jackson编写完整的Json字符串不是问题，但使用仅代表其中一小部分的Java对象更新现有字符串要困难得多。
数据存储问题：
private static class DataStore {
private final String data;
private DataStore(Customer customer, BrowserInfo browser) throws IOException, JSONException {
StringWriter sw = new StringWriter(1000);
try (JsonGenerator jgen = MAPPER.getJsonFactory().createJsonGenerator(sw)) {
jgen.writeStartObject();
writeBunchOfProperties(jgen);
jgen.writeFieldName("customer");
jgen.writeRawValue(MAPPER.writeValueAsString(customer));
writeBunchOfProperties(jgen);
jgen.writeFieldName("browser");
jgen.writeRawValue(MAPPER.writeValueAsString(browser));
writeBunchOfProperties(jgen);
jgen.writeEndObject();
}
this.data = sw.toString();
}
private void writeBunchOfProperties(JsonGenerator jgen) throws IOException {
int c = new Random().nextInt(3) + 1;
for (int i = 0; i < c; ++i) {
jgen.writeFieldName(RandomStringUtils.random(10));
jgen.writeRawValue(JSON_LONG);
}
}
public String readData(String query) {
return data;
}
private void saveData(String json) {
// Not implemented
}
public void saveData(JSONObject json) {
saveData(json.toString());
}
public void saveData(Object obj) throws IOException {
// problem: ?
}
public <T> T readData(String query, Class<T> clazz) throws IOException {
return MAPPER.readValue(readData(query), clazz);
}
public <T> T readDataForUpdating(String query, Class<T> clazz) throws IOException {
// problem: ?
}
在更高级别，我希望能够做到这样的事情：
public long doSomeWritingWithJackson() throws IOException {
t0 = System.nanoTime();
KnownPart obj = store.readDataForUpdating(null, KnownPart.class);
obj.customer.name = "Jackson Doe";
obj.browser.version = "10";
store.saveData(obj);
t1 = System.nanoTime();
return t1 - t0;
}
不丢失我保存时未读取的数据。 显然，我不想第二次读取数据，因为我是从远程主机读取它而我不想将它缓存在某个静态/实例映射中，因为我需要它在一个静态/实例映射中仍然非常有效高度并发的环境。
所以解决方案，简而言之就是： - 首先读取json字符串的树，然后使用它将Json对象反序列化为Java对象。 - 存储deserialize对象（在KnowPart类中）并将树存储在某个父抽象类中 - 编写一个Jackson模块来定制bean的序列化方式。代码与原始代码几乎相同，区别在于当写入KnownPart中的属性时，它的键被删除了UnknownPart对象中的树，然后很容易编写未知部分... < / p>
主要对象变为：
private static abstract class UnknownPart {
ObjectNode tree;
}
private static class KnownPart extends UnknownPart {
@JsonProperty
private Customer customer;
@JsonProperty
private BrowserInfo browser;
}
该模块仅处理UnknownPart对象： 私有静态类MyModule扩展了模块{
@Override
public String getModuleName() {
return "MyModule";
}
@Override
public Version version() {
return new Version(0, 0, 1, "SNAPSHOT");
}
@Override
public void setupModule(Module.SetupContext context) {
context.addBeanSerializerModifier(new org.codehaus.jackson.map.ser.BeanSerializerModifier() {
private UnknownPartSerializer cs;
@Override
public JsonSerializer modifySerializer(SerializationConfig config, BasicBeanDescription beanDesc, JsonSerializer<?> serializer) {
return UnknownPart.class.isAssignableFrom(beanDesc.getBeanClass())
? new UnknownPartSerializer((BeanSerializerBase) serializer)
: serializer;
}
});
}
}
序列化器是：
private static class UnknownPartSerializer extends BeanSerializerBase {
public UnknownPartSerializer(BeanSerializerBase src) {
super(src);
}
@Override
public void serialize(Object bean, JsonGenerator jgen, SerializerProvider provider) throws IOException, JsonGenerationException {
UnknownPart up = (UnknownPart) bean;
jgen.writeStartObject();
serializeFields(up, jgen, provider);
jgen.writeEndObject();
}
protected void serializeFields(UnknownPart bean, JsonGenerator jgen, SerializerProvider provider) throws IOException, JsonGenerationException {
final BeanPropertyWriter[] props;
if (_filteredProps != null && provider.getSerializationView() != null) {
props = _filteredProps;
} else {
props = _props;
}
int i = 0;
try {
for (final int len = props.length; i < len; ++i) {
BeanPropertyWriter prop = props[i];
if (prop != null) { // can have nulls in filtered list
prop.serializeAsField(bean, jgen, provider);
bean.tree.remove(prop.getName()); // new
}
}
if (_anyGetterWriter != null) {
_anyGetterWriter.getAndSerialize(bean, jgen, provider);
}
// new:
Iterator<Entry<String, JsonNode>> it = bean.tree.getFields();
while (it.hasNext()) {
Entry<String, JsonNode> e = it.next();
jgen.writeFieldName(e.getKey());
jgen.writeObject(e.getValue());
}
} catch (Exception e) {
String name = (i == props.length) ? "[anySetter]"
: props[i].getName();
wrapAndThrow(provider, e, bean, name);
} catch (StackOverflowError e) {
/* 04-Sep-2009, tatu: Dealing with this is tricky, since we do not
* have many stack frames to spare... just one or two; can't
* make many calls.
*/
JsonMappingException mapE = new JsonMappingException("Infinite recursion (StackOverflowError)", e);
String name = (i == props.length) ? "[anySetter]"
: props[i].getName();
mapE.prependPath(new JsonMappingException.Reference(bean, name));
throw mapE;
}
}
}
与此同时，我写了一个基准来确认（或不是）这个解决方案比JSONObject更快的大Json字符串...... 测试比较： - 使用JSONObject读取（无映射） - 读杰克逊 - 与杰克逊一起读树 - 使用JSONObject读/写 - 与杰克逊读/写 它确实更快:)）
在1000次迭代之后，排除了潜在的类加载或JVM所做的一些初始化，我得到了，在纳秒内：
-- AVERAGE ----------------------------------------------------------------------------
| 1| 860,560| 157,772| 234,654| 1,595,018| 488,427|
---------------------------------------------------------------------------------------
| | RO JSONObject| RO Jackson| R/- Jackson| R/W JSONObject| R/W Jackson|
---------------------------------------------------------------------------------------
答案 1 :(得分：2)
包含基准的完整可执行文件源是：
import java.io.IOException;
import java.io.StringWriter;
import java.util.Iterator;
import java.util.Map.Entry;
import java.util.Random;
import org.apache.commons.lang3.RandomStringUtils;
import org.apache.commons.lang3.StringUtils;
import org.codehaus.jackson.JsonGenerationException;
import org.codehaus.jackson.JsonGenerator;
import org.codehaus.jackson.JsonNode;
import org.codehaus.jackson.Version;
import org.codehaus.jackson.annotate.JsonProperty;
import org.codehaus.jackson.map.DeserializationConfig;
import org.codehaus.jackson.map.JsonMappingException;
import org.codehaus.jackson.map.JsonSerializer;
import org.codehaus.jackson.map.Module;
import org.codehaus.jackson.map.ObjectMapper;
import org.codehaus.jackson.map.SerializationConfig;
import org.codehaus.jackson.map.SerializerProvider;
import org.codehaus.jackson.map.introspect.BasicBeanDescription;
import org.codehaus.jackson.map.ser.BeanPropertyWriter;
import org.codehaus.jackson.map.ser.std.BeanSerializerBase;
import org.codehaus.jackson.node.ObjectNode;
import org.json.JSONException;
import org.json.JSONObject;
public class JacksonModule {
private static final ObjectMapper MAPPER = new ObjectMapper();
private static final int COUNT = 0;
private static final int REPEAT_HEADER = 40;
static {
MAPPER.configure(DeserializationConfig.Feature.FAIL_ON_UNKNOWN_PROPERTIES, false);
MAPPER.configure(SerializationConfig.Feature.WRITE_NULL_PROPERTIES, false);
MAPPER.registerModule(new MyModule());
}
private DataProcessor sdp;
private long[] sum = new long[5];
public static void main(String[] args) throws IOException, JSONException {
new JacksonModule().start();
}
public JacksonModule() throws IOException, JSONException {
this.sdp = new DataProcessor();
}
public void start() throws IOException, JSONException {
run(-1, false); // load classes: slow
if (COUNT > 0) {
for (int i = 0; i < COUNT; ++i) {
if (i % REPEAT_HEADER == 0) {
System.out.println("---------------------------------------------------------------------------------------");
print("", "RO JSONObject", "RO Jackson", "R/- Jackson", "R/W JSONObject", "R/W Jackson");
System.out.println("---------------------------------------------------------------------------------------");
}
run(i, true);
}
System.out.println("-- AVERAGE ----------------------------------------------------------------------------");
print(1, sum[0] / COUNT, sum[1] / COUNT, sum[2] / COUNT, sum[3] / COUNT, sum[4] / COUNT);
System.out.println("---------------------------------------------------------------------------------------");
print("", "RO JSONObject", "RO Jackson", "R/- Jackson", "R/W JSONObject", "R/W Jackson");
System.out.println("---------------------------------------------------------------------------------------");
}
}
public void run(int i, boolean print) throws JSONException, IOException {
long t1 = sdp.doReadWithJSONObject();
long t2 = sdp.doReadWithJackson();
long t3 = sdp.doReadForUpdatingWithJacksonButDontWrite();
long t4 = sdp.doSomeWritingWithJSONObject();
long t5 = sdp.doSomeWritingWithJackson();
if (print) {
print(i, t1, t2, t3, t4, t5);
sum[0] += t1;
sum[1] += t2;
sum[2] += t3;
sum[3] += t4;
sum[4] += t5;
}
}
private void print(int index, long t1, long t2, long t3, long t4, long t5) {
print(Integer.toString(index), String.format("%,d", t1), String.format("%,d", t2), String.format("%,d", t3), String.format("%,d", t4), String.format("%,d", t5));
}
private void print(String i0, String a, String b, String c, String d, String e) {
System.out.println("|"
+ StringUtils.leftPad(i0, 5) + "|"
+ StringUtils.leftPad(a, 15) + "|"
+ StringUtils.leftPad(b, 15) + "|"
+ StringUtils.leftPad(c, 15) + "|"
+ StringUtils.leftPad(d, 15) + "|"
+ StringUtils.leftPad(e, 15) + "|");
}
private static class DataProcessor {
private DataStore store;
private long t0, t1;
private DataProcessor() throws IOException, JSONException {
this.store = new DataStore(customer, browser);
}
public long doReadWithJSONObject() throws JSONException {
t0 = System.nanoTime();
JSONObject json = new JSONObject(store.readData(null)); // can throw JSONException
JSONObject customer = json.getJSONObject("customer"); // can throw JSONException
JSONObject browserInfo = json.getJSONObject("browser"); // can throw JSONException
// need to do manually the mapping and figure out what is exactly in this object. Hell no!
t1 = System.nanoTime();
return t1 - t0;
}
public long doReadWithJackson() throws IOException {
t0 = System.nanoTime();
KnownPart obj = store.readData(null, KnownPart.class);
t1 = System.nanoTime();
return t1 - t0;
}
public long doReadForUpdatingWithJacksonButDontWrite() throws IOException {
t0 = System.nanoTime();
KnownPart obj = store.readDataForUpdating(null, KnownPart.class);
t1 = System.nanoTime();
return t1 - t0;
}
public long doSomeWritingWithJSONObject() throws JSONException {
t0 = System.nanoTime();
JSONObject json = new JSONObject(store.readData(null)); // can throw JSONException
JSONObject customer = json.getJSONObject("customer"); // can throw JSONException
JSONObject browserInfo = json.getJSONObject("browser"); // can throw JSONException
customer.put("name", "Jackson Doe");
browserInfo.put("version", "10");
store.saveData(json);
t1 = System.nanoTime();
return t1 - t0;
}
public long doSomeWritingWithJackson() throws IOException {
t0 = System.nanoTime();
KnownPart obj = store.readDataForUpdating(null, KnownPart.class);
obj.customer.name = "Jackson Doe";
obj.browser.version = "10";
store.saveData(obj);
t1 = System.nanoTime();
return t1 - t0;
}
}
private static class DataStore {
private final String data;
private DataStore(Customer customer, BrowserInfo browser) throws IOException, JSONException {
StringWriter sw = new StringWriter(1000);
try (JsonGenerator jgen = MAPPER.getJsonFactory().createJsonGenerator(sw)) {
jgen.writeStartObject();
writeBunchOfProperties(jgen);
jgen.writeFieldName("customer");
jgen.writeRawValue(MAPPER.writeValueAsString(customer));
writeBunchOfProperties(jgen);
jgen.writeFieldName("browser");
jgen.writeRawValue(MAPPER.writeValueAsString(browser));
writeBunchOfProperties(jgen);
jgen.writeEndObject();
}
this.data = sw.toString();
}
private void writeBunchOfProperties(JsonGenerator jgen) throws IOException {
int c = new Random().nextInt(3) + 1;
for (int i = 0; i < c; ++i) {
jgen.writeFieldName(RandomStringUtils.random(10));
jgen.writeRawValue(JSON_LONG);
}
}
public String readData(String query) {
return data;
}
private void saveData(String json) {
// TODO
}
public void saveData(JSONObject json) {
saveData(json.toString());
}
public void saveData(Object obj) throws IOException {
saveData(MAPPER.writeValueAsString(obj));
}
public <T> T readData(String query, Class<T> clazz) throws IOException {
return MAPPER.readValue(readData(query), clazz);
}
public <T extends UnknownPart> T readDataForUpdating(String query, Class<T> clazz) throws IOException {
ObjectNode root = (ObjectNode) MAPPER.readTree(readData(query));
T obj = MAPPER.readValue(root, clazz);
obj.tree = root;
return obj;
}
}
private static abstract class UnknownPart {
ObjectNode tree;
}
private static class KnownPart extends UnknownPart {
@JsonProperty
private Customer customer;
@JsonProperty
private BrowserInfo browser;
}
private static class Customer {
@JsonProperty
private int id;
@JsonProperty
private String name;
@JsonProperty
private Address[] addresses; // just to make it more complex for this example
public Customer(int id, String name, Address[] addresses) {
this.id = id;
this.name = name;
this.addresses = addresses;
}
public Customer() {
}
}
private static class Address {
@JsonProperty
private String street;
@JsonProperty
private String city;
public Address(String street, String city) {
this.street = street;
this.city = city;
}
public Address() {
}
}
private static class BrowserInfo {
@JsonProperty
private String agent;
@JsonProperty
private String version;
public BrowserInfo(String agent, String version) {
this.agent = agent;
this.version = version;
}
public BrowserInfo() {
}
}
private static class MyModule extends Module {
@Override
public String getModuleName() {
return "MyModule";
}
@Override
public Version version() {
return new Version(0, 0, 1, "SNAPSHOT");
}
@Override
public void setupModule(Module.SetupContext context) {
context.addBeanSerializerModifier(new org.codehaus.jackson.map.ser.BeanSerializerModifier() {
private UnknownPartSerializer cs;
@Override
public JsonSerializer modifySerializer(SerializationConfig config, BasicBeanDescription beanDesc, JsonSerializer<?> serializer) {
return UnknownPart.class.isAssignableFrom(beanDesc.getBeanClass())
? new UnknownPartSerializer((BeanSerializerBase) serializer)
: serializer;
}
});
}
}
private static class UnknownPartSerializer extends BeanSerializerBase {
public UnknownPartSerializer(BeanSerializerBase src) {
super(src);
}
@Override
public void serialize(Object bean, JsonGenerator jgen, SerializerProvider provider) throws IOException, JsonGenerationException {
UnknownPart up = (UnknownPart) bean;
jgen.writeStartObject();
serializeFields(up, jgen, provider);
jgen.writeEndObject();
}
protected void serializeFields(UnknownPart bean, JsonGenerator jgen, SerializerProvider provider) throws IOException, JsonGenerationException {
final BeanPropertyWriter[] props;
if (_filteredProps != null && provider.getSerializationView() != null) {
props = _filteredProps;
} else {
props = _props;
}
int i = 0;
try {
for (final int len = props.length; i < len; ++i) {
BeanPropertyWriter prop = props[i];
if (prop != null) { // can have nulls in filtered list
prop.serializeAsField(bean, jgen, provider);
bean.tree.remove(prop.getName());
}
}
if (_anyGetterWriter != null) {
_anyGetterWriter.getAndSerialize(bean, jgen, provider);
}
Iterator<Entry<String, JsonNode>> it = bean.tree.getFields();
while (it.hasNext()) {
Entry<String, JsonNode> e = it.next();
jgen.writeFieldName(e.getKey());
jgen.writeObject(e.getValue());
}
} catch (Exception e) {
String name = (i == props.length) ? "[anySetter]"
: props[i].getName();
wrapAndThrow(provider, e, bean, name);
} catch (StackOverflowError e) {
/* 04-Sep-2009, tatu: Dealing with this is tricky, since we do not
* have many stack frames to spare... just one or two; can't
* make many calls.
*/
JsonMappingException mapE = new JsonMappingException("Infinite recursion (StackOverflowError)", e);
String name = (i == props.length) ? "[anySetter]"
: props[i].getName();
mapE.prependPath(new JsonMappingException.Reference(bean, name));
throw mapE;
}
}
}
private static Customer customer = new Customer(1, "John Doe", new Address[]{
new Address("broadway av", "new york"),
new Address("peachtree st", "atlanta")
});
private static BrowserInfo browser = new BrowserInfo("IE", "6.0");
// some json found on the internet
private static final String JSON_LONG = "{\"web-app\": {"
+ "\"servlet\": ["
+ "{"
+ "\"servlet-name\": \"cofaxCDS\","
+ "\"servlet-class\": \"org.cofax.cds.CDSServlet\","
+ "\"init-param\": {"
+ "\"configGlossary:installationAt\": \"Philadelphia, PA\","
+ "\"configGlossary:adminEmail\": \"ksm@pobox.com\","
+ "\"configGlossary:poweredBy\": \"Cofax\","
+ "\"configGlossary:poweredByIcon\": \"/images/cofax.gif\","
+ "\"configGlossary:staticPath\": \"/content/static\","
+ "\"templateProcessorClass\": \"org.cofax.WysiwygTemplate\","
+ "\"templateLoaderClass\": \"org.cofax.FilesTemplateLoader\","
+ "\"templatePath\": \"templates\","
+ "\"templateOverridePath\": \"\","
+ "\"defaultListTemplate\": \"listTemplate.htm\","
+ "\"defaultFileTemplate\": \"articleTemplate.htm\","
+ "\"useJSP\": false,"
+ "\"jspListTemplate\": \"listTemplate.jsp\","
+ "\"jspFileTemplate\": \"articleTemplate.jsp\","
+ "\"cachePackageTagsTrack\": 200,"
+ "\"cachePackageTagsStore\": 200,"
+ "\"cachePackageTagsRefresh\": 60,"
+ "\"cacheTemplatesTrack\": 100,"
+ "\"cacheTemplatesStore\": 50,"
+ "\"cacheTemplatesRefresh\": 15,"
+ "\"cachePagesTrack\": 200,"
+ "\"cachePagesStore\": 100,"
+ "\"cachePagesRefresh\": 10,"
+ "\"cachePagesDirtyRead\": 10,"
+ "\"searchEngineListTemplate\": \"forSearchEnginesList.htm\","
+ "\"searchEngineFileTemplate\": \"forSearchEngines.htm\","
+ "\"searchEngineRobotsDb\": \"WEB-INF/robots.db\","
+ "\"useDataStore\": true,"
+ "\"dataStoreClass\": \"org.cofax.SqlDataStore\","
+ "\"redirectionClass\": \"org.cofax.SqlRedirection\","
+ "\"dataStoreName\": \"cofax\","
+ "\"dataStoreDriver\": \"com.microsoft.jdbc.sqlserver.SQLServerDriver\","
+ "\"dataStoreUrl\": \"jdbc:microsoft:sqlserver://LOCALHOST:1433;DatabaseName=goon\","
+ "\"dataStoreUser\": \"sa\","
+ "\"dataStorePassword\": \"dataStoreTestQuery\","
+ "\"dataStoreTestQuery\": \"SET NOCOUNT ON;select test='test';\","
+ "\"dataStoreLogFile\": \"/usr/local/tomcat/logs/datastore.log\","
+ "\"dataStoreInitConns\": 10,"
+ "\"dataStoreMaxConns\": 100,"
+ "\"dataStoreConnUsageLimit\": 100,"
+ "\"dataStoreLogLevel\": \"debug\","
+ "\"maxUrlLength\": 500}},"
+ "{"
+ "\"servlet-name\": \"cofaxEmail\","
+ "\"servlet-class\": \"org.cofax.cds.EmailServlet\","
+ "\"init-param\": {"
+ "\"mailHost\": \"mail1\","
+ "\"mailHostOverride\": \"mail2\"}},"
+ "{"
+ "\"servlet-name\": \"cofaxAdmin\","
+ "\"servlet-class\": \"org.cofax.cds.AdminServlet\"},"
+ ""
+ "{"
+ "\"servlet-name\": \"fileServlet\","
+ "\"servlet-class\": \"org.cofax.cds.FileServlet\"},"
+ "{"
+ "\"servlet-name\": \"cofaxTools\","
+ "\"servlet-class\": \"org.cofax.cms.CofaxToolsServlet\","
+ "\"init-param\": {"
+ "\"templatePath\": \"toolstemplates/\","
+ "\"log\": 1,"
+ "\"logLocation\": \"/usr/local/tomcat/logs/CofaxTools.log\","
+ "\"logMaxSize\": \"\","
+ "\"dataLog\": 1,"
+ "\"dataLogLocation\": \"/usr/local/tomcat/logs/dataLog.log\","
+ "\"dataLogMaxSize\": \"\","
+ "\"removePageCache\": \"/content/admin/remove?cache=pages&id=\","
+ "\"removeTemplateCache\": \"/content/admin/remove?cache=templates&id=\","
+ "\"fileTransferFolder\": \"/usr/local/tomcat/webapps/content/fileTransferFolder\","
+ "\"lookInContext\": 1,"
+ "\"adminGroupID\": 4,"
+ "\"betaServer\": true}}],"
+ "\"servlet-mapping\": {"
+ "\"cofaxCDS\": \"/\","
+ "\"cofaxEmail\": \"/cofaxutil/aemail/*\","
+ "\"cofaxAdmin\": \"/admin/*\","
+ "\"fileServlet\": \"/static/*\","
+ "\"cofaxTools\": \"/tools/*\"},"
+ ""
+ "\"taglib\": {"
+ "\"taglib-uri\": \"cofax.tld\","
+ "\"taglib-location\": \"/WEB-INF/tlds/cofax.tld\"}}}";
}
答案 2 :(得分：1)
我能想象到的最简单的解决方案是将您的JSON反序列化为Map类（例如LinkedHashMap）。请看下面的例子：
import java.util.LinkedHashMap;
import com.fasterxml.jackson.databind.ObjectMapper;
public class JacksonProgram {
public static void main(String[] args) throws Exception {
ObjectMapper mapper = new ObjectMapper();
String json = "{\"a\":\"java.lang.Integer\",\"b\":\"time json\",\"c\":\"action json\",\"d\":[1,2,3]}";
System.out.println(json);
LinkedHashMap<String, Object> map = mapper.readValue(json, LinkedHashMap.class);
map.put("b", "Override property or create new");
System.out.println(mapper.writeValueAsString(map));
}
}
以上程序打印：
{"a":"java.lang.Integer","b":"time json","c":"action json","d":[1,2,3]}
{"a":"java.lang.Integer","b":"Override property or create new","c":"action json","d":[1,2,3]}
如果要更改路径上的内部属性，可以通过以下方式实现它：
import java.io.IOException;
import java.util.Arrays;
import java.util.Collection;
import java.util.LinkedHashMap;
import java.util.LinkedList;
import com.fasterxml.jackson.databind.ObjectMapper;
public class JacksonProgram {
public static void main(String[] args) throws IOException {
ObjectMapper mapper = new ObjectMapper();
String json = "{\"b\":{\"bb\":{\"bbb\":20}}}";
System.out.println(json);
LinkedHashMap<String, Object> map = mapper.readValue(json, LinkedHashMap.class);
JsonUpdater updater = new JsonUpdater(map);
updater.update(Arrays.asList("b", "bb", "bbb"), 4);
System.out.println(mapper.writeValueAsString(map));
}
}
class JsonUpdater {
private LinkedHashMap<String, Object> jsonMap;
public JsonUpdater(LinkedHashMap<String, Object> jsonMap) {
this.jsonMap = jsonMap;
}
public boolean update(Collection<String> propertiesOnThePath, Object newValue) {
LinkedList<String> path = new LinkedList<String>(propertiesOnThePath);
String lastProperty = path.removeLast();
LinkedHashMap<String, Object> objectMap = jsonMap;
while (!path.isEmpty()) {
String property = path.poll();
if (!objectMap.containsKey(property)) {
return false;
}
objectMap = (LinkedHashMap<String, Object>) objectMap.get(property);
}
if (!objectMap.containsKey(lastProperty)) {
return false;
}
objectMap.put(lastProperty, newValue);
return false;
}
}
以上程序打印：
{"b":{"bb":{"bbb":20}}}
{"b":{"bb":{"bbb":4}}}
我们可以看到：价值已发生变化。但是这个解决方案有很大的缺点 - 我们必须反序列化所有JSON。几千字节字符串不是Java的问题，但如果你真的想要优化你的程序，你可以使用ObjectNode类和ObjectMapper#readTree方法。请参阅以下源代码：
import com.fasterxml.jackson.databind.ObjectMapper;
import com.fasterxml.jackson.databind.node.ObjectNode;
public class JacksonProgram {
public static void main(String[] args) throws Exception {
ObjectMapper mapper = new ObjectMapper();
String json = "{\"a\":\"java.lang.Integer\",\"b\":\"time json\",\"c\":\"action json\",\"d\":[1,2,3]}";
System.out.println(json);
ObjectNode jsonTree = (ObjectNode) mapper.readTree(json);
jsonTree.put("b", "Override property or create new");
System.out.println(jsonTree.toString());
}
}
以上程序打印：
{"a":"java.lang.Integer","b":"time json","c":"action json","d":[1,2,3]}
{"a":"java.lang.Integer","b":"Override property or create new","c":"action json","d":[1,2,3]}
我没有进行任何比较测试，但您可以测试哪种解决方案更快。