对于想了解如何优雅的使用Objects.requireNonNull(Tobj,Stringmessage)定制你的NPE异常的读者，本文将是一篇不可错过的文章，并且为您提供关于#-net-canno

对于想了解如何优雅的使用Objects.requireNonNull(T obj, String message)定制你的NPE异常的读者，本文将是一篇不可错过的文章，并且为您提供关于# - net - cannot access a disposed object r nobject name filebufferingreadstream、@Nonnull和Objects.requireNonNull有什么区别、avro-rpc 中协议定义的 request 的模式与 GenericRequest.request (String messageName, Object request) 中的 request 是一致对应的关系么、c# – 无法将System.Data.Entity.Core.Objects.ObjectResult类型隐式转换为System.Data.Objects.ObjectResult的有价值信息。

• 如何优雅的使用Objects.requireNonNull(T obj, String message)定制你的NPE异常
• # - net - cannot access a disposed object r nobject name filebufferingreadstream
• @Nonnull和Objects.requireNonNull有什么区别
• avro-rpc 中协议定义的 request 的模式与 GenericRequest.request (String messageName, Object request) 中的 request 是一致对应的关系么
• c# – 无法将System.Data.Entity.Core.Objects.ObjectResult类型隐式转换为System.Data.Objects.ObjectResult

如何优雅的使用Objects.requireNonNull(T obj, String message)定制你的NPE异常

IDEA中习惯跟踪源码实现逻辑，多次碰到Objects.requireNonNull(T obj)这个方法，改方法主要用于提早判断对象是否为空，以便更早的抛出NPE

平时小组开发中强调程序健壮性，不允许组员的代码中出现明显的NPE,这样多数时候都要写判空逻辑，抛出自定义的异常

我们看下具体的源码：

/**
 * Checks that the specified object reference is not {@code null}.
 * This method is designed primarily for doing parameter validation in methods
 * and constructors, as demonstrated below:
 * <blockquote><pre>
 * public Foo(Bar bar) {
 *     this.bar = Objects.requireNonNull(bar);
 * }
 * </pre></blockquote>
 *
 * @param obj the object reference to check for nullity
 * @param <T> the type of the reference
 * @return {@code obj} if not {@code null}
 * @throws NullPointerException if {@code obj} is {@code null}
 */
public static <T> T requireNonNull(T obj) {
    if (obj == null)
        throw new NullPointerException();
    return obj;
}
解释：检查定义的对象引用不为空。设计该方法主要用来做方法和构造函数中的参数校验
如上，如果直接使用仍然是抛出一个NPE，除了能提早检测和抛出异常，无法直接在业务中使用

继续往下滚动，发现还有这个方法

/**
 * Checks that the specified object reference is not {@code null} and
 * throws a customized {@link NullPointerException} if it is. This method
 * is designed primarily for doing parameter validation in methods and
 * constructors with multiple parameters, as demonstrated below:
 * <blockquote><pre>
 * public Foo(Bar bar, Baz baz) {
 *     this.bar = Objects.requireNonNull(bar, "bar must not be null");
 *     this.baz = Objects.requireNonNull(baz, "baz must not be null");
 * }
 * </pre></blockquote>
 *
 * @param obj     the object reference to check for nullity
 * @param message detail message to be used in the event that a {@code
 *                NullPointerException} is thrown
 * @param <T> the type of the reference
 * @return {@code obj} if not {@code null}
 * @throws NullPointerException if {@code obj} is {@code null}
 */
public static <T> T requireNonNull(T obj, String message) {
    if (obj == null)
        throw new NullPointerException(message);
    return obj;
}

and throws a customized {@link NullPointerException} if it is：定制的空指针异常

and constructors with multiple parameters ：多参数的构造函数

这样，下次我们想抛出一个自定义的空指针异常的时候,以前是：
if（obj==null）{
　　throw new xxxException("该记录不存在xxxx");
}

现在可以更优雅的写Objects.requireNonNull(T obj,"该记录不存在xxxx")

代码实现区别不大，那么为啥不选择优雅^_^

# - net - cannot access a disposed object r nobject name filebufferingreadstream

public class AppContractResolver : DefaultContractResolver { private readonly IServiceProvider _services; public AppContractResolver(IServiceProvider services) { _services = services; } protected override IList<JsonProperty> CreateProperties(Type type, MemberSerialization memberSerialization) { var httpContextAccessor = _services.GetService<IHttpContextAccessor>(); var user = httpContextAccessor.HttpContext.User; List<JsonProperty> properies = base.CreateProperties(type, memberSerialization).ToList(); properies = FilterOneClaimGranted(type, properies, user); return properies; }

var httpContextAccessor = _services.GetService<IHttpContextAccessor>();

- $exception    {System.ObjectDisposedException: Cannot access a disposed object. Object name: ''IServiceProvider''. at Microsoft.Extensions.DependencyInjection.ServiceLookup.ThrowHelper.ThrowObjectDisposedException() at Microsoft.Extensions.DependencyInjection.ServiceLookup.ServiceProviderEngineScope.GetService(Type serviceType) at Microsoft.Extensions.DependencyInjection.ServiceProviderServiceExtensions.GetService[T](IServiceProvider provider) at WebAPI.Extensions.AppContractResolver.CreateProperties(Type type, MemberSerialization memberSerialization) in C:\Users\luukw\Desktop\stage\blacky-api\Blacky\Extensions\Resolver\AppContractResolver.cs:line 25 at Newtonsoft.Json.Serialization.DefaultContractResolver.CreateObjectContract(Type objectType) at Newtonsoft.Json.Serialization.DefaultContractResolver.CreateContract(Type objectType) at System.Collections.Concurrent.ConcurrentDictionary`2.GetOrAdd(TKey key, Func`2 valueFactory) at Newtonsoft.Json.Serialization.DefaultContractResolver.ResolveContract(Type type) at Newtonsoft.Json.Serialization.JsonSerializerInternalReader.GetContractSafe(Type type) at Newtonsoft.Json.Serialization.JsonSerializerInternalReader.Deserialize(JsonReader reader, Type objectType, Boolean checkAdditionalContent) at Newtonsoft.Json.JsonSerializer.DeserializeInternal(JsonReader reader, Type objectType) at Newtonsoft.Json.JsonSerializer.Deserialize(JsonReader reader, Type objectType) at Microsoft.AspNetCore.Mvc.Formatters.JsonInputFormatter.ReadRequestBodyAsync(InputFormatterContext context, Encoding encoding)} System.ObjectDisposedException

 public void ConfigureServices(IServiceCollection services) { … services.AddHttpContextAccessor(); … }

     public void Configure(IApplicationBuilder app, IHttpContextAccessor accessor) { ... ...accessor.HttpContext.RequestService ... }

public void Configure(IApplicationBuilder app, IHostingEnvironment env, IServiceProvider services) { var svc = services.GetService<IServiceProvider>(); // <-- exception here }

public void Configure(IApplicationBuilder app, IHostingEnvironment env) { var svc = app.ApplicationServices.GetService<IServiceProvider>(); // no exception }

@Nonnull和Objects.requireNonNull有什么区别

public Integer getId(@Nonnull SomeObject obj){  
    // do some stuff
    return id;
}

public Integer getId(SomeObject obj){   
    Objects.requireNonNull(SomeObject,"SomeObject is null");
    // do some stuff
    return id;
}

avro-rpc 中协议定义的 request 的模式与 GenericRequest.request (String messageName, Object request) 中的 request 是一致对应的关系么

@蝙蝠 你好，想请教个问题：在 avro-rpc 中，如果协议是下面这样子：

{
  "namespace": "com.acme",
  "protocol": "HelloWorld",
  "doc": "Protocol Greetings",

  "types": [
    {"name": "Greeting", "type": "record", "fields": [
      {"name": "message", "type": "string"}]},
    {"name": "Curse", "type": "error", "fields": [
      {"name": "message", "type": "string"}]}
  ],

  "messages": {
    "hello": {
      "doc": "Say hello.",
      "request": [{"name": "greeting", "type": "Greeting" }],
      "response": "Greeting",
      "errors": ["Curse"]
    }
  }
}

public Object GenericRequest.request(String messageName, Object request)
               throws IOException

c# – 无法将System.Data.Entity.Core.Objects.ObjectResult类型隐式转换为System.Data.Objects.ObjectResult

MyStoredProc_Result r = dbcontext.MyStoredPoc();

MyStoredProc_Result r = dbcontext.MyStoredPoc().FirstOrDefault();

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