3-配置

# 基础配置
```js
{
  "greeting": {
    "morning": "Good morning!",
    "afternoon": "Good afternoon!",
    "evening": "Good evening!"
  }
}
```

```java
public interface IGreeter
{
    string Greet(DateTimeOffset time);
}

public class Greeter : IGreeter
{
    private readonly IConfiguration _configuration;
    public Greeter(IConfiguration configuration)    => _configuration = configuration.GetSection("greeting");

public string Greet(DateTimeOffset time) => time.Hour switch
    {
        var h when h >= 5 && h < 12 	=> _configuration["morning"],
        var h when h >= 12 && h < 17 	=> _configuration["afternoon"],
        _ 				=> _configuration["evening"],
    };
}
```
```java
public class GreetingMiddleware
{
    private readonly IGreeter _greeter;
    public GreetingMiddleware(RequestDelegate _, IGreeter greeter)=> _greeter = greeter;
    public Task InvokeAsync(HttpContext context)
    => context.Response.WriteAsync(_greeter.Greet(DateTimeOffset.Now));
}
```
```java
var builder = WebApplication.CreateBuilder(args);
builder.Services.AddSingleton<IGreeter, Greeter>();
var app = builder.Build();
app.UseMiddleware<GreetingMiddleware>();
app.Run();
```

# 选项配置

```java
 public interface IGreeter
 {
     string Greet(DateTimeOffset time);
 }
 
public class GreetingOptions
{
    public string Morning { get; set; } = default!;
    public string Afternoon { get; set; } = default!;
    public string Evening { get; set; } = default!;
}

public class Greeter : IGreeter
{
    private readonly GreetingOptions _options;
    public Greeter(IOptions<GreetingOptions> optionsAccessor) => _options = optionsAccessor.Value;
    public string Greet(DateTimeOffset time) => time.Hour switch
    {
        var h when h >= 5 && h < 12 => _options.Morning,
        var h when h >= 12 && h < 17 => _options.Afternoon,
        _ => _options.Evening
    };
}
```
```java
public class GreetingMiddleware
{
    private readonly IGreeter _greeter;
    public GreetingMiddleware(RequestDelegate _, IGreeter greeter)=> _greeter = greeter;
    public Task InvokeAsync(HttpContext context)
    => context.Response.WriteAsync(_greeter.Greet(DateTimeOffset.Now));
}
```

```java
var builder = WebApplication.CreateBuilder(args);
builder.Services
    .AddSingleton<IGreeter, Greeter>()
    .Configure<GreetingOptions>(builder.Configuration.GetSection("greeting"));
var app = builder.Build();
app.UseMiddleware<GreetingMiddleware>();
app.Run();
```