我有一个类来保存一些json数据，如下所示：
package org.swx.nursing.tools.configuration.data;
import java.util.Set;
import com.cerner.system.exception.Verifier;
import com.cerner.system.exception.VerifyException;
import com.google.common.collect.ImmutableSet;
/**
* Class representing a simple {@link JsonData#identifier},
* {@link JsonData#data} format. This class can be used to
* persist application data for example in a Configuration file.
*
* @author SW029693
* @since v1.0
*/
public class JsonData <T>{
/**
* Represents a unique identifier
*/
private String identifier;
/**
* Represents the data pertaining to this {@link JsonData#identifier}
*/
private T data;
private static final Set<String> VALID_JSON_ID_TYPES = ImmutableSet.of("CONFIG","HOTKEYS");
public JsonData(String identifier, T data) {
super();
this.identifier = identifier;
this.data = data;
}
/**
* Getter for {@link JsonData#identifier}
* @return
*/
public String getIdentifier() {
return identifier;
}
/**
* Sets the {@link JsonData#identifier} to the given value
* @param identifier
* Represents a unique {@link JsonData#identifier}
* @throws VerifyException
* If the argument is {@code null} or {@code empty}
*/
public void setIdentifier(String identifier) throws VerifyException{
Verifier.verifyNotNull(identifier, "identifier : null");
Verifier.verifyNotEmpty(identifier,"identifier : empty");
this.identifier = identifier;
}
/**
* Getter for {@link JsonData}
* @return
*/
public T getData() {
return data;
}
/**
* Sets the {@link JsonData#data} to the given value
* @param identifier
* Represents a unique {@link JsonData#data}
* @throws VerifyException
* If the argument is {@code null}
*/
public void setData(T data) {
Verifier.verifyNotNull(data, "data : null");
this.data = data;
}
@Override
public String toString() {
return "JsonData [identifier=" + identifier + ", data=" + data + "]";
}
}
我正在尝试将一些数据转换为JSON（将其写入文件），将其读回并转换为上面的JsonData对象。这是我的单元测试失败了：
@Test
@SuppressWarnings("unchecked")
public void testWriteContentsToFile() {
ConfigurationManager<JsonData> configurationManager = (ConfigurationManager<JsonData>)
ConfigurationManager.Factory.create();
assertNotNull(configurationManager);
configurationManager.write(getMockJsonData());
System.out.println("1="+getMockJsonData().getData().toString());
assertEquals(getMockJsonData().getData(), ((JsonData) readconfigFile()).getData());
}
此测试的辅助方法如下：
/**
* Helper method to read the config.json file
* @return
*/
private static JsonData<ConfigurationProperty> readconfigFile() {
Reader reader = null;
JsonData<ConfigurationProperty> data = null;
Gson gson = null;
try {
reader = new FileReader("./config.json");
gson = new GsonBuilder().create();
data = gson.fromJson(reader, JsonData.class);
System.out.println("yooo="+data.getData().getRunnableContext());
} catch (FileNotFoundException e) {
e.printStackTrace();
fail("Test failed while reading the config.json file: "+e.getMessage()); }
finally {
try {
reader.close();
} catch (IOException e) {
e.printStackTrace();
fail("Test failed while reading the config.json file: "+e.getMessage());
}
}
return data;
}
和
/**
* Helper method which creates a mock {@link JsonData} object for testing purposes
*
* @return An instance of the newly created mock {@link Jsondata} object
*/
private static JsonData<ConfigurationProperty> getMockJsonData() {
JsonData<ConfigurationProperty> data = new JsonData<ConfigurationProperty>("CONFIG",
getMockConfigurationProperty("testKey", "testContext", "APPLICATION"));
System.out.println("data ==="+data);
return data;
}
/**
* Helper method which creates a {@link ConfigurationProperty} based on the given
* non-null and non-empty arguments. This method can be used to get the
* {@link ConfigurationProperty} instance created with the desired fields when ALL
* of the 3 parameters are non-null, non-empty & valid.
*
* @param mockHotKey
* A non-null & non-empty mockHotkey parameter passed in as an argument
*
* @param mockContext
* A non-null & non-empty mockContext parameter passed in as an argument
*
* @param mockContextType
* A non-null & non-empty mockContextType parameter passed in as an argument
*
* @throws VerifierException
* If the argument validation for non-null or non-empty arguments as failed.
*
* @throws IllegalArgumentException
* The {@link ConfigurationProperty.Builder#withRunnableContextType(String type) method
* throws an {@link IllegalArgumentException} if the provided type is not supported in
* {@link ConfigurationProperty#RUNNABLE_CONTEXT_TYPE}
*
* @return An instance of newly created {@link ConfigurationProperty} object
*/
private static ConfigurationProperty getMockConfigurationProperty (
String mockHotKey, String mockContext, String mockContextType) {
Verifier.verifyNotNull(mockHotKey);
Verifier.verifyNotNull(mockContext);
Verifier.verifyNotNull(mockContextType);
Verifier.verifyNotEmpty(mockHotKey);
Verifier.verifyNotEmpty(mockContext);
Verifier.verifyNotEmpty(mockContextType);
return ConfigurationProperty.Builder
.create()
.withHotKey(mockHotKey)
.withRunnableContext(mockContext)
.withRunnableContextType(mockContextType)
.build();
}
当我运行单元测试以将json文件中的数据读入我的JsonData对象时，我收到以下错误：
java.lang.ClassCastException: com.google.gson.internal.LinkedTreeMap cannot be cast to org.swx.nursing.tools.configuration.data.ConfigurationProperty
at org.swx.nursing.tools.configuration.data.ConfigurationManagerImplTest.readconfigFile(ConfigurationManagerImplTest.java:181)
at org.swx.nursing.tools.configuration.data.ConfigurationManagerImplTest.testWriteContentsToFile(ConfigurationManagerImplTest.java:166)
at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:39)
at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:25)
at java.lang.reflect.Method.invoke(Method.java:597)
at org.junit.internal.runners.TestMethod.invoke(TestMethod.java:66)
at org.jmock.integration.junit4.JMock$1.invoke(JMock.java:37)
at org.junit.internal.runners.MethodRoadie.runTestMethod(MethodRoadie.java:105)
at org.junit.internal.runners.MethodRoadie$2.run(MethodRoadie.java:86)
at org.junit.internal.runners.MethodRoadie.runBeforesThenTestThenAfters(MethodRoadie.java:94)
at org.junit.internal.runners.MethodRoadie.runTest(MethodRoadie.java:84)
at org.junit.internal.runners.MethodRoadie.run(MethodRoadie.java:49)
at org.junit.internal.runners.JUnit4ClassRunner.invokeTestMethod(JUnit4ClassRunner.java:98)
at org.junit.internal.runners.JUnit4ClassRunner.runMethods(JUnit4ClassRunner.java:61)
at org.junit.internal.runners.JUnit4ClassRunner$1.run(JUnit4ClassRunner.java:54)
at org.junit.internal.runners.ClassRoadie.runUnprotected(ClassRoadie.java:34)
at org.junit.internal.runners.ClassRoadie.runProtected(ClassRoadie.java:44)
at org.junit.internal.runners.JUnit4ClassRunner.run(JUnit4ClassRunner.java:52)
at org.eclipse.jdt.internal.junit4.runner.JUnit4TestReference.run(JUnit4TestReference.java:49)
at org.eclipse.jdt.internal.junit.runner.TestExecution.run(TestExecution.java:38)
at org.eclipse.jdt.internal.junit.runner.RemoteTestRunner.runTests(RemoteTestRunner.java:467)
at org.eclipse.jdt.internal.junit.runner.RemoteTestRunner.runTests(RemoteTestRunner.java:683)
at org.eclipse.jdt.internal.junit.runner.RemoteTestRunner.run(RemoteTestRunner.java:390)
at org.eclipse.jdt.internal.junit.runner.RemoteTestRunner.main(RemoteTestRunner.java:197)
文件写得像这样：
{
"identifier": "CONFIG",
"data": {
"hotKey": "testKey",
"type": "APPLICATION",
"runnableContext": "testContext"
}
}
我无法阅读＆＃39;数据＆＃39;由于上述错误，以上json写入JsonData对象的文件中的一部分。
请告知
由于
答案 0 :(得分：2)
请参阅https://sites.google.com/site/gson/gson-user-guide#TOC-Serializing-and-Deserializing-Generic-Types
当你调用toJson（obj）时，Gson调用obj.getClass（）来获取有关要序列化的字段的信息。类似地，您通常可以在fromJson（json，MyClass.class）方法中传递MyClass.class对象。如果对象是非泛型类型，则此方法正常。但是，如果对象是泛型类型，则由于Java类型擦除而丢失通用类型信息。这是一个说明这一点的例子：
class Foo<T> {
T value;
}
Gson gson = new Gson();
Foo<Bar> foo = new Foo<Bar>();
gson.toJson(foo); // May not serialize foo.value correctly
gson.fromJson(json, foo.getClass()); // Fails to deserialize foo.value as Bar
上面的代码无法将值解释为类型Bar，因为Gson调用list.getClass（）来获取其类信息，但此方法返回一个原始类Foo.class。这意味着Gson无法知道这是Foo类型的对象，而不仅仅是普通的Foo。
您可以通过为通用类型指定正确的参数化类型来解决此问题。您可以使用TypeToken类来完成此操作。
Type fooType = new TypeToken<Foo<Bar>>() {}.getType();
gson.toJson(foo, fooType);
gson.fromJson(json, fooType);
用于获取fooType的习惯用法实际上定义了一个匿名本地内部类，其中包含一个返回完全参数化类型的方法getType（）。