这是我第一次使用 json 和 java。我检查了很多问题/帖子与我的错误相同。但是没有找到有用的东西。
我知道我必须不添加任何 args 构造函数。我做了，但它没有帮助我。仍然出现同样的错误。它可以这样工作。我认为这与我的代码非常复杂的继承有关。
错误:
SEVERE: Servlet.service() for servlet [dispatcher] in context with path [/derp] threw exception [Request processing failed; nested exception is java.lang.RuntimeException: Failed to invoke public com.derp.procedure.model.SkeletonElement() with no args] with root cause java.lang.InstantiationException
堆栈跟踪:
gru 19, 2014 8:27:50 PM org.apache.catalina.core.StandardWrapperValve invoke
SEVERE: Servlet.service() for servlet [dispatcher] in context with path [/derp] threw exception [Request processing failed; nested exception is java.lang.RuntimeException: Failed to invoke public com.derp.procedure.model.SkeletonElement() with no args] with root cause
java.lang.InstantiationException
at sun.reflect.InstantiationExceptionConstructorAccessorImpl.newInstance(InstantiationExceptionConstructorAccessorImpl.java:48)
at java.lang.reflect.Constructor.newInstance(Constructor.java:408)
at com.google.gson.internal.ConstructorConstructor$3.construct(ConstructorConstructor.java:104)
at com.google.gson.internal.bind.ReflectiveTypeAdapterFactory$Adapter.read(ReflectiveTypeAdapterFactory.java:186)
at com.google.gson.internal.bind.TypeAdapterRuntimeTypeWrapper.read(TypeAdapterRuntimeTypeWrapper.java:40)
at com.google.gson.internal.bind.CollectionTypeAdapterFactory$Adapter.read(CollectionTypeAdapterFactory.java:81)
at com.google.gson.internal.bind.CollectionTypeAdapterFactory$Adapter.read(CollectionTypeAdapterFactory.java:60)
at com.google.gson.Gson.fromJson(Gson.java:810)
at com.google.gson.Gson.fromJson(Gson.java:775)
at com.google.gson.Gson.fromJson(Gson.java:724)
at com.derp.procedure.model.SkeletonElement.toObject(SkeletonElement.java:38)
at com.derp.procedure.model.Skeleton.setSkeletonElements(Skeleton.java:53)
at com.derp.procedure.controller.ProcedureController.elementsAssignmentSubmit(ProcedureController.java:81)
at com.derp.procedure.controller.ProcedureController$$FastClassBySpringCGLIB$$35de90ba.invoke(<generated>)
at org.springframework.cglib.proxy.MethodProxy.invoke(MethodProxy.java:204)
at org.springframework.aop.framework.CglibAopProxy$CglibMethodInvocation.invokeJoinpoint(CglibAopProxy.java:717)
at org.springframework.aop.framework.ReflectiveMethodInvocation.proceed(ReflectiveMethodInvocation.java:157)
at org.springframework.transaction.interceptor.TransactionInterceptor$1.proceedWithInvocation(TransactionInterceptor.java:98)
at org.springframework.transaction.interceptor.TransactionAspectSupport.invokeWithinTransaction(TransactionAspectSupport.java:266)
at org.springframework.transaction.interceptor.TransactionInterceptor.invoke(TransactionInterceptor.java:95)
at org.springframework.aop.framework.ReflectiveMethodInvocation.proceed(ReflectiveMethodInvocation.java:179)
at org.springframework.aop.framework.CglibAopProxy$DynamicAdvisedInterceptor.intercept(CglibAopProxy.java:653)
at com.derp.procedure.controller.ProcedureController$$EnhancerBySpringCGLIB$$fe2945ed.elementsAssignmentSubmit(<generated>)
at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
at java.lang.reflect.Method.invoke(Method.java:483)
at org.springframework.web.method.support.InvocableHandlerMethod.invoke(InvocableHandlerMethod.java:215)
at org.springframework.web.method.support.InvocableHandlerMethod.invokeForRequest(InvocableHandlerMethod.java:132)
at org.springframework.web.servlet.mvc.method.annotation.ServletInvocableHandlerMethod.invokeAndHandle(ServletInvocableHandlerMethod.java:104)
at org.springframework.web.servlet.mvc.method.annotation.RequestMappingHandlerAdapter.invokeHandleMethod(RequestMappingHandlerAdapter.java:781)
at org.springframework.web.servlet.mvc.method.annotation.RequestMappingHandlerAdapter.handleInternal(RequestMappingHandlerAdapter.java:721)
at org.springframework.web.servlet.mvc.method.AbstractHandlerMethodAdapter.handle(AbstractHandlerMethodAdapter.java:83)
at org.springframework.web.servlet.DispatcherServlet.doDispatch(DispatcherServlet.java:943)
at org.springframework.web.servlet.DispatcherServlet.doService(DispatcherServlet.java:877)
at org.springframework.web.servlet.FrameworkServlet.processRequest(FrameworkServlet.java:966)
at org.springframework.web.servlet.FrameworkServlet.doPut(FrameworkServlet.java:879)
at javax.servlet.http.HttpServlet.service(HttpServlet.java:647)
at org.springframework.web.servlet.FrameworkServlet.service(FrameworkServlet.java:842)
at javax.servlet.http.HttpServlet.service(HttpServlet.java:725)
at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:291)
at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:206)
at org.springframework.web.filter.HiddenHttpMethodFilter.doFilterInternal(HiddenHttpMethodFilter.java:77)
at org.springframework.web.filter.OncePerRequestFilter.doFilter(OncePerRequestFilter.java:107)
at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:239)
at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:206)
at org.apache.tomcat.websocket.server.WsFilter.doFilter(WsFilter.java:52)
at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:239)
at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:206)
at org.apache.catalina.core.StandardWrapperValve.invoke(StandardWrapperValve.java:219)
at org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java:106)
at org.apache.catalina.authenticator.AuthenticatorBase.invoke(AuthenticatorBase.java:503)
at org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:136)
at org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:79)
at org.apache.catalina.valves.AbstractAccessLogValve.invoke(AbstractAccessLogValve.java:610)
at org.apache.catalina.core.StandardEngineValve.invoke(StandardEngineValve.java:88)
at org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:526)
at org.apache.coyote.http11.AbstractHttp11Processor.process(AbstractHttp11Processor.java:1078)
at org.apache.coyote.AbstractProtocol$AbstractConnectionHandler.process(AbstractProtocol.java:655)
at org.apache.coyote.http11.Http11Protocol$Http11ConnectionHandler.process(Http11Protocol.java:146)
at org.apache.tomcat.util.net.JIoEndpoint$SocketProcessor.run(JIoEndpoint.java:279)
at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1142)
at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:617)
at org.apache.tomcat.util.threads.TaskThread$WrappingRunnable.run(TaskThread.java:61)
at java.lang.Thread.run(Thread.java:745)
我的 java 类:
扩展的通用模型类:
package com.derp.generic.model;
import java.io.IOException;
import javax.persistence.GeneratedValue;
import javax.persistence.GenerationType;
import javax.persistence.Id;
import javax.persistence.MappedSuperclass;
import javax.persistence.Transient;
import org.apache.commons.lang.builder.ToStringBuilder;
import org.apache.commons.lang.builder.ToStringStyle;
import org.codehaus.jackson.JsonGenerationException;
import org.codehaus.jackson.annotate.JsonMethod;
import org.codehaus.jackson.annotate.JsonAutoDetect.Visibility;
import org.codehaus.jackson.map.JsonMappingException;
import org.codehaus.jackson.map.ObjectMapper;
@MappedSuperclass
public abstract class GenericModel<T extends GenericModel<?>> {
@Id
@GeneratedValue(strategy = GenerationType.AUTO)
private Long id;
public long getId() {return id;}
public void setId(long id) {this.id = id;}
public GenericModel() {
}
// a toString method that can be used in any class.
// uses reflection to dynamically print java class field
// values one line at a time.
@Override
public String toString() {
return ToStringBuilder.reflectionToString(this, ToStringStyle.MULTI_LINE_STYLE);
}
public String toJson() {
ObjectMapper jsonMapper = new ObjectMapper();
try {
return jsonMapper.writerWithDefaultPrettyPrinter().writeValueAsString(this);
} catch (JsonGenerationException e) {
e.printStackTrace();
return null;
} catch (JsonMappingException e) {
e.printStackTrace();
return null;
} catch (IOException e) {
e.printStackTrace();
return null;
}
}
//public GenericModel<T> toObject(String jsonObject) {
//Suggested by stackOverflowComunity at:
//https://stackoverflow.com/questions/27532206/java-create-list-of-objects-from-json-string-with-jackson
public <T> T toObject(String jsonObject) {
ObjectMapper jsonMapper = new ObjectMapper();
try {
//GenericModel<T> t = jsonMapper.readValue(jsonObject, GenericModel.class);
T t = (T) jsonMapper.readValue(jsonObject, GenericModel.class);
//return t;
return t;
} catch (JsonGenerationException e) {
e.printStackTrace();
return null;
} catch (JsonMappingException e) {
e.printStackTrace();
return null;
} catch (IOException e) {
e.printStackTrace();
return null;
}
}
}
扩展通用模型的通用层次类:
package com.derp.generic.model;
import java.io.IOException;
import java.util.LinkedList;
import java.util.List;
import javax.persistence.CascadeType;
import javax.persistence.FetchType;
import javax.persistence.ManyToOne;
import javax.persistence.MappedSuperclass;
import javax.persistence.OneToMany;
import org.codehaus.jackson.JsonGenerationException;
import org.codehaus.jackson.map.JsonMappingException;
import org.codehaus.jackson.map.ObjectMapper;
@MappedSuperclass
public abstract class GenericHierarchicalModel<T extends GenericHierarchicalModel<T>> extends GenericModel<T> {
private String name;
@ManyToOne(fetch = FetchType.LAZY, cascade = CascadeType.ALL)
private T parent;
@OneToMany(mappedBy = "parent")
private List<T> children;
public String getName() {return name;}
public void setName(String name) {this.name = name;}
public T getParent() {return parent;}
public void setParent(T parent) {this.parent = parent;}
public List<T> getChildren() {return children;}
public void setChildren(List<T> children) {this.children = children;}
public GenericHierarchicalModel() {
super();
}
@Override
public String toJson() {
return "{\"title\":\"" + this.name + "\", \"id\":\"" + this.getId() + "\", \"children\": [" + listToJson(this.getChildren()) + "]}";
}
public String listToJson(List<T> children) {
String json = "";
for(int i=0; i<children.size(); i++) {
json = json + children.get(i).toJson();
if(children.size()!=i+1) {
json = json + ", ";
}
}
return json;
}
// @Override
// public GenericHierarchicalModel<T> toObject(String jsonObject) {
// int start = 0; // '(' position in string
// int end = 0; // ')' position in string
// for(int i = 0; i < jsonObject.length(); i++) {
// if(jsonObject.charAt(i) == '{') // Looking for '{' position in string
// start = i;
// else if(jsonObject.charAt(i) == '}') // Looking for '}' position in string
// end = i;
// }
// String number = jsonObject.substring(start+1, end); // you take value between start and end
// System.out.println(number);
// return null;
// }
}
我试图从 json 对象列表中反序列化的模型类:
package com.derp.procedure.model;
import java.io.IOException;
import java.util.List;
import javax.persistence.DiscriminatorColumn;
import javax.persistence.Entity;
import javax.persistence.Inheritance;
import javax.persistence.InheritanceType;
import javax.persistence.Table;
import javax.persistence.Transient;
import org.codehaus.jackson.JsonGenerationException;
import org.codehaus.jackson.map.JsonMappingException;
import org.codehaus.jackson.map.ObjectMapper;
import com.derp.generic.model.GenericHierarchicalModel;
import com.derp.generic.model.GenericModel;
import com.google.gson.Gson;
import com.google.gson.reflect.TypeToken;
@Entity
@Table(name="procedure__SkeletonElement")
@Inheritance(strategy=InheritanceType.JOINED)
@DiscriminatorColumn(name="type")
public abstract class SkeletonElement extends GenericHierarchicalModel<SkeletonElement> {
@Transient
public String getDecriminatorValue() {
return this.getClass().getSimpleName();
}
@Override
public String toJson() {
return "{\"title\":\"" + this.getName() + "\", \"id\":\"" + this.getId() + "\", \"type\":\"" + this.getDecriminatorValue() + "\", \"children\": [" + listToJson(this.getChildren()) + "]}";
}
public List<SkeletonElement> toObject(String jsonObject) {
Gson gson = new Gson(); // Or use new GsonBuilder().create();
//SkeletonElement[] target2 = gson.fromJson(jsonObject, SkeletonElement[].class);
List<SkeletonElement> target2 = gson.fromJson(jsonObject, new TypeToken<List<SkeletonElement>>(){}.getType());
return target2;
}
public SkeletonElement() {
super();
}
}
以及包含我试图反序列化回 java 对象列表的对象集合的类:
package com.derp.procedure.model;
import java.util.LinkedList;
import java.util.List;
import javax.persistence.CascadeType;
import javax.persistence.Entity;
import javax.persistence.FetchType;
import javax.persistence.ManyToMany;
import javax.persistence.Table;
import com.derp.generic.model.GenericDictionaryModel;
@Entity
@Table(name="procedure__Skeleton")
public class Skeleton extends GenericDictionaryModel<Skeleton> {
@ManyToMany(fetch = FetchType.EAGER, cascade = CascadeType.ALL)
private List<SkeletonElement> skeletonElements;
public void setSkeletonElements(List<SkeletonElement> skeletonElements) {this.skeletonElements = skeletonElements;}
public List<SkeletonElement> getSkeletonElements() {return skeletonElements;}
public List<SkeletonElement> getSkeletonParentsElements() {
List<SkeletonElement> skeletonParentsElements = new LinkedList<SkeletonElement>();
for(int i=0; i<this.skeletonElements.size(); i++) {
if(this.skeletonElements.get(i).getParent()==null) {
skeletonParentsElements.add(this.getSkeletonElements().get(i));
}
}
return skeletonParentsElements;
}
public Skeleton(String name) {
super(name);
}
public Skeleton() {
// TODO Auto-generated constructor stub
}
public String getSkeletonElementsJsonTree() {
String jsonTreeString ="[";
List<SkeletonElement> skeletonParentsElements = getSkeletonParentsElements();
for(int i=0; i<skeletonParentsElements.size(); i++) {
jsonTreeString = jsonTreeString + skeletonParentsElements.get(i).toJson();
if((1+i) != skeletonParentsElements.size()) {
jsonTreeString = jsonTreeString + ",";
}
}
return jsonTreeString + "]";
}
public void setSkeletonElements(String skeletonElementsJson) {
this.skeletonElements.get(0).toObject(skeletonElementsJson);
}
}
至少我不会反序列化的 json 字符串:
[
{
"name": "Title1",
"id": "1",
"type": "SkeletonJobElement",
"parent_id": "null",
"children": [
{
"name": "Title11",
"id": "2",
"type": "SkeletonJobElement",
"parent_id": "1",
"children": [
{
"name": "Title111",
"id": "5",
"type": "SkeletonFileElement",
"parent_id": "2",
"children": []
},
{
"name": "Title112",
"id": "6",
"type": "SkeletonFileElement",
"parent_id": "2",
"children": []
}
]
}
]
},
{
"name": "Title2",
"id": "3",
"type": "SkeletonJobElement",
"parent_id": "null",
"children": [
{
"name": "Title21",
"id": "4",
"type": "SkeletonJobElement",
"parent_id": "3",
"children": []
}
]
}
]
我知道要分析的代码很多，但请帮我弄清楚。 我为此苦苦挣扎了一周。
最佳答案
com.derp.procedure.model.SkeletonElement 是一个抽象类。使这个类具体删除抽象修饰符。
关于java - Gson 反序列化 json。 java.lang.RuntimeException : Failed to invoke public com. derp.procedure.model.SkeletonElement() with no args] 根本原因，我们在Stack Overflow上找到一个类似的问题： https://stackoverflow.com/questions/27572831/