{"id":680,"date":"2023-02-26T14:38:22","date_gmt":"2023-02-26T06:38:22","guid":{"rendered":"https:\/\/www.appblog.cn\/?p=680"},"modified":"2023-04-29T18:22:17","modified_gmt":"2023-04-29T10:22:17","slug":"usage-instructions-for-typereference-in-java","status":"publish","type":"post","link":"https:\/\/www.appblog.cn\/index.php\/2023\/02\/26\/usage-instructions-for-typereference-in-java\/","title":{"rendered":"Java\u4e2dTypeReference\u7528\u6cd5\u8bf4\u660e"},"content":{"rendered":"

TypeReference\u7528\u9014<\/h2>\n

\u5728\u4f7f\u7528FastJson\u65f6\uff0c\u5bf9\u4e8e\u6cdb\u578b\u7684\u53cd\u5e8f\u5217\u5316\u5f88\u591a\u573a\u666f\u4e0b\u90fd\u4f1a\u4f7f\u7528\u5230TypeReference<\/code>\uff0c\u4f8b\u5982\uff1a<\/p>\n

void testTypeReference() {\n    List<Integer> list = new ArrayList<>();\n    list.add(1);\n    list.add(9);\n    list.add(4);\n    list.add(8);\n    JSONObject jsonObj = new JSONObject();\n    jsonObj.put("a", list);\n    System.out.println(jsonObj);\n\n    List<String> list2 = jsonObj.getObject("a", new TypeReference<List<Integer>>(){});\n    System.out.println(list2);\n}<\/code><\/pre>\n
<\/p>\n
\u8f93\u51fa<\/p>\n
{"a":[1,9,4,8]}\n[1, 9, 4, 8]<\/code><\/pre>\n
TypeReference\u6e90\u7801<\/h2>\n
\u4f7f\u7528TypeReference<\/code>\u53ef\u4ee5\u660e\u786e\u7684\u6307\u5b9a\u53cd\u5e8f\u5217\u5316\u7684\u7c7b\u578b\uff0c\u5177\u4f53\u5b9e\u73b0\u903b\u8f91\u53c2\u8003TypeReference<\/code>\u7684\u6784\u9020\u51fd\u6570\u3000<\/p>\n
protected TypeReference() {\n    Type superClass = getClass().getGenericSuperclass();\n\n    Type type = ((ParameterizedType) superClass).getActualTypeArguments()[0];\n\n    Type cachedType = classTypeCache.get(type);\n    if (cachedType == null) {\n        classTypeCache.putIfAbsent(type, type);\n        cachedType = classTypeCache.get(type);\n    }\n\n    this.type = cachedType;\n}<\/code><\/pre>\n
\u5176\u4e2d\u6838\u5fc3\u7684\u65b9\u6cd5\u662f\uff1agetActualTypeArguments<\/code>\uff0c\u5b83\u53ef\u4ee5\u5f97\u5230\u7236\u7c7b\u7684\u53cd\u7701\u7c7b\u578b<\/p>\n
ParameterizedType<\/code>\u662f\u4e00\u4e2a\u8bb0\u5f55\u7c7b\u578b\u6cdb\u578b\u7684\u63a5\u53e3\uff0c\u7ee7\u627f\u81eaType<\/code>\uff0c\u4e00\u5171\u4e09\u65b9\u6cd5:<\/p>\n
Type[] getActualTypeArguments(); \/\/\u8fd4\u56de\u6cdb\u578b\u7c7b\u578b\u6570\u7ec4\nType getRawType(); \/\/\u8fd4\u56de\u539f\u59cb\u7c7b\u578bType\nType getOwnerType(); \/\/\u8fd4\u56de Type \u5bf9\u8c61\uff0c\u8868\u793a\u6b64\u7c7b\u578b\u662f\u5176\u6210\u5458\u4e4b\u4e00\u7684\u7c7b\u578b\u3002<\/code><\/pre>\n
\u4f8b\u5982Map<String, String><\/code>\u5bf9\u5e94\u7684ParameterizedType<\/code>\u4e09\u4e2a\u65b9\u6cd5\u5206\u522b\u53d6\u503c\u5982\u4e0b\uff1a<\/p>\n
[class java.lang.String, class java.lang.String]\ninterface java.util.Map\nnull<\/code><\/pre>\n
TypeReference\u4f8b\u8bc1<\/h2>\n
import java.lang.reflect.ParameterizedType;\nimport java.lang.reflect.Type;\nimport java.util.HashMap;\nimport java.util.Map;\n\npublic class TypeReferencBaseLearn {\n    public static class IntMap extends HashMap<String, Integer> {}\n\n    void test1() {\n        IntMap intMap = new IntMap();\n        System.out.println("getSuperclass:" + intMap.getClass().getSuperclass());\n        System.out.println("getGenericSuperclass:" + intMap.getClass().getGenericSuperclass());\n        Type type = intMap.getClass().getGenericSuperclass();\n        if (type instanceof ParameterizedType) {\n            ParameterizedType p = (ParameterizedType) type;\n            for (Type t : p.getActualTypeArguments()) {\n                System.out.println(t);\n            }\n        }\n    }\n\n    void test2() {\n        Map<String, Integer> intMap = new HashMap<>();\n        System.out.println("\\ngetSuperclass:" + intMap.getClass().getSuperclass());\n        System.out.println("getGenericSuperclass:" + intMap.getClass().getGenericSuperclass());\n        Type type = intMap.getClass().getGenericSuperclass();\n        if (type instanceof ParameterizedType) {\n            ParameterizedType p = (ParameterizedType) type;\n            for (Type t : p.getActualTypeArguments()) {\n                System.out.println(t);\n            }\n        }\n    }\n\n    void test3() {\n        Map<String, Integer> intMap = new HashMap<String, Integer>(){};\n        System.out.println("\\ngetSuperclass:" + intMap.getClass().getSuperclass());\n        System.out.println("getGenericSuperclass:" + intMap.getClass().getGenericSuperclass());\n        Type type = intMap.getClass().getGenericSuperclass();\n        if (type instanceof ParameterizedType) {\n            ParameterizedType p = (ParameterizedType) type;\n            for (Type t : p.getActualTypeArguments()) {\n                System.out.println(t);\n            }\n        }\n    }\n\n    public static void main(String[] args) {\n        TypeReferencBaseLearn obj = new TypeReferencBaseLearn();\n        obj.test1();\n        obj.test2();\n        obj.test3();\n    }\n}<\/code><\/pre>\n
\u8f93\u51fa<\/p>\n
getSuperclass:class java.util.HashMap\ngetGenericSuperclass:java.util.HashMap<java.lang.String, java.lang.Integer>\nclass java.lang.String\nclass java.lang.Integer\n\ngetSuperclass:class java.util.AbstractMap\ngetGenericSuperclass:java.util.AbstractMap<K, V>\nK\nV\n\ngetSuperclass:class java.util.HashMap\ngetGenericSuperclass:java.util.HashMap<java.lang.String, java.lang.Integer>\nclass java.lang.String\nclass java.lang.Integer<\/code><\/pre>\n","protected":false},"excerpt":{"rendered":"
TypeReference\u7528\u9014 \u5728\u4f7f\u7528FastJson\u65f6\uff0c\u5bf9\u4e8e\u6cdb\u578b\u7684\u53cd\u5e8f\u5217\u5316\u5f88\u591a\u573a\u666f\u4e0b\u90fd\u4f1a\u4f7f\u7528\u5230TypeRef […]<\/p>\n","protected":false},"author":1,"featured_media":0,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[43],"tags":[],"class_list":["post-680","post","type-post","status-publish","format-standard","hentry","category-java-basic"],"_links":{"self":[{"href":"https:\/\/www.appblog.cn\/index.php\/wp-json\/wp\/v2\/posts\/680","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/www.appblog.cn\/index.php\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/www.appblog.cn\/index.php\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/www.appblog.cn\/index.php\/wp-json\/wp\/v2\/users\/1"}],"replies":[{"embeddable":true,"href":"https:\/\/www.appblog.cn\/index.php\/wp-json\/wp\/v2\/comments?post=680"}],"version-history":[{"count":0,"href":"https:\/\/www.appblog.cn\/index.php\/wp-json\/wp\/v2\/posts\/680\/revisions"}],"wp:attachment":[{"href":"https:\/\/www.appblog.cn\/index.php\/wp-json\/wp\/v2\/media?parent=680"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/www.appblog.cn\/index.php\/wp-json\/wp\/v2\/categories?post=680"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/www.appblog.cn\/index.php\/wp-json\/wp\/v2\/tags?post=680"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}