Jackson之路
考虑到您没有描述数据结构的POJO，可以简单地执行以下操作：
final String json = "{"contentType": "foo", "fooField1": ... }";final ObjectNode node = new ObjectMapper().readValue(json, ObjectNode.class);// ^ // actually, try and *reuse* a single instance of ObjectMapperif (node.has("contentType")) { System.out.println("contentType: " + node.get("contentType"));}解决评论部分中的问题
但是，如果您不希望消耗整个源
String，而只是访问其路径已知的特定属性，则必须使用Tokeniser自己编写。
实际上，这是周末，我有时间在手上，所以我可以给您一个良好的开端：这是一个基本的开始！它可以在
strict模式下运行并发出明智的错误消息，或者宽容并
Optional.empty在无法满足请求时返回。
public static class JSonPath { protected static final JsonFactory JSON_FACTORY = new JsonFactory(); private final List<JSONKey> keys; public JSonPath(final String from) { this.keys = Arrays.stream((from.startsWith("[") ? from : String.valueOf("." + from)) .split("(?=\[|\]|\.)")) .filter(x -> !"]".equals(x)) .map(JSONKey::new) .collect(Collectors.toList()); } public Optional<String> getWithin(final String json) throws IOException { return this.getWithin(json, false); } public Optional<String> getWithin(final String json, final boolean strict) throws IOException { try (final InputStream stream = new StringInputStream(json)) { return this.getWithin(stream, strict); } } public Optional<String> getWithin(final InputStream json) throws IOException { return this.getWithin(json, false); } public Optional<String> getWithin(final InputStream json, final boolean strict) throws IOException { return getValueAt(JSON_FACTORY.createParser(json), 0, strict); } protected Optional<String> getValueAt(final JsonParser parser, final int idx, final boolean strict) throws IOException { try { if (parser.isClosed()) { return Optional.empty(); } if (idx >= this.keys.size()) { parser.nextToken(); if (null == parser.getValueAsString()) { throw new JSonPathException("The selected node is not a leaf"); } return Optional.of(parser.getValueAsString()); } this.keys.get(idx).advanceCursor(parser); return getValueAt(parser, idx + 1, strict); } catch (final JSonPathException e) { if (strict) { throw (null == e.getCause() ? new JSonPathException(e.getMessage() + String.format(", at path: '%s'", this.toString(idx)), e) : e); } return Optional.empty(); } } @Override public String toString() { return ((Function<String, String>) x -> x.startsWith(".") ? x.substring(1) : x) .apply(this.keys.stream().map(JSONKey::toString).collect(Collectors.joining())); } private String toString(final int idx) { return ((Function<String, String>) x -> x.startsWith(".") ? x.substring(1) : x) .apply(this.keys.subList(0, idx).stream().map(JSONKey::toString).collect(Collectors.joining())); } @SuppressWarnings("serial") public static class JSonPathException extends RuntimeException { public JSonPathException() { super(); } public JSonPathException(final String message) { super(message); } public JSonPathException(final String message, final Throwable cause) { super(message, cause); } public JSonPathException(final Throwable cause) { super(cause); } } private static class JSonKey { private final String key; private final JsonToken startToken; public JSonKey(final String str) { this(str.substring(1), str.startsWith("[") ? JsonToken.START_ARRAY : JsonToken.START_OBJECT); } private JSonKey(final String key, final JsonToken startToken) { this.key = key; this.startToken = startToken; } public void advanceCursor(final JsonParser parser) throws IOException { final JsonToken token = parser.nextToken(); if (!this.startToken.equals(token)) { throw new JSonPathException(String.format("Expected token of type '%s', got: '%s'", this.startToken, token)); } if (JsonToken.START_ARRAY.equals(this.startToken)) { // Moving cursor within a JSON Array for (int i = 0; i != Integer.valueOf(this.key).intValue(); i++) { JSONKey.skipTonext(parser); } } else { // Moving cursor in a JSON Object String name; for (parser.nextToken(), name = parser.getCurrentName(); !this.key.equals(name); parser.nextToken(), name = parser.getCurrentName()) { JSONKey.skipTonext(parser); } } } private static void skipTonext(final JsonParser parser) throws IOException { final JsonToken token = parser.nextToken(); if (JsonToken.START_ARRAY.equals(token) || JsonToken.START_OBJECT.equals(token) || JsonToken.FIELD_NAME.equals(token)) { skipTonextImpl(parser, 1); } else if (JsonToken.END_ARRAY.equals(token) || JsonToken.END_OBJECT.equals(token)) { throw new JSonPathException("Could not find requested key"); } } private static void skipTonextImpl(final JsonParser parser, final int depth) throws IOException { if (depth == 0) { return; } final JsonToken token = parser.nextToken(); if (JsonToken.START_ARRAY.equals(token) || JsonToken.START_OBJECT.equals(token) || JsonToken.FIELD_NAME.equals(token)) { skipTonextImpl(parser, depth + 1); } else { skipTonextImpl(parser, depth - 1); } } @Override public String toString() { return String.format(this.startToken.equals(JsonToken.START_ARRAY) ? "[%s]" : ".%s", this.key); } }}假设以下JSON内容：
{ "people": [{ "name": "Eric", "age": 28 }, { "name": "Karin", "age": 26 }], "company": { "name": "Elm Farm", "address": "3756 Preston Street Wichita, KS 67213", "phone": "857-778-1265" }}…您可以
JSONPath按如下方式使用我的课程：
final String json = "{"people":[],"company":{}}"; // refer to JSON above System.out.println(new JSonPath("people[0].name").getWithin(json)); // Optional[Eric] System.out.println(new JSonPath("people[1].name").getWithin(json)); // Optional[Karin] System.out.println(new JSonPath("people[2].name").getWithin(json)); // Optional.empty System.out.println(new JSonPath("people[0].age").getWithin(json)); // Optional[28] System.out.println(new JSonPath("company").getWithin(json)); // Optional.empty System.out.println(new JSonPath("company.name").getWithin(json)); // Optional[Elm Farm]请记住，这是 基本的 。它不强制数据类型（返回的每个值都是
String），仅返回叶节点。
实际测试案例
它处理
InputStreams，因此您可以针对一些巨大的JSON文档进行测试，并发现它比浏览器下载并显示其内容要快得多：
System.out.println(new JSonPath("info.contact.email") .getWithin(new URL("http://test-api.rescuegroups.org/v5/public/swagger.php").openStream()));// Optional[support@rescuegroups.org]快速测试
请注意，我没有重用任何现有的，
JSONPath否则
ObjectMapper结果是不准确的-无论如何，这只是一个非常粗略的比较：
public static Long time(final Callable<?> r) throws Exception { final long start = System.currentTimeMillis(); r.call(); return Long.valueOf(System.currentTimeMillis() - start);}public static void main(final String[] args) throws Exception { final URL url = new URL("http://test-api.rescuegroups.org/v5/public/swagger.php"); System.out.println(String.format( "%dms to get 'info.contact.email' with JSONPath", time(() -> new JSonPath("info.contact.email").getWithin(url.openStream())))); System.out.println(String.format( "%dms to just download the entire document otherwise", time(() -> new Scanner(url.openStream()).useDelimiter("\A").next()))); System.out.println(String.format( "%dms to bluntly map it entirely with Jackson and access a specific field", time(() -> new ObjectMapper() .readValue(url.openStream(), ObjectNode.class) .get("info").get("contact").get("email"))));}378ms即可使用JSONPath获得“ info.contact.email”
756ms即可下载整个文档，否则需要
896ms才能完全通过Jackson映射并访问特定字段
