Java的列舉與註解

阿新 • • 發佈：2020-12-14

一、列舉類

JDK1.5之前需要自定義列舉類；JDK 1.5 新增的 enum 關鍵字用於定義列舉類。若列舉只有一個成員, 則可以作為一種單例模式的實現方式

1.1 列舉類的屬性

列舉類物件的屬性不應允許被改動, 所以應該使用 private final 修飾。
列舉類的使用 private final 修飾的屬性應該在構造器中為其賦值。
若列舉類顯式的定義了帶引數的構造器, 則在列出列舉值時也必須對應的傳入引數。

1.2 Enum列舉類

必須在列舉類的第一行宣告列舉類物件。 JDK 1.5 中可以在 switch 表示式中使用Enum定義的列舉類的物件作為表示式, case 子句可以直接使用列舉值的名字, 無需新增列舉類作為限定。
列舉類和普通類的區別：
使用 enum 定義的列舉類預設繼承了 java.lang.Enum 類
列舉類的構造器只能使用 private 訪問控制符
列舉類的所有例項必須在列舉類中顯式列出(, 分隔 ; 結尾). 列出的例項系統會自動新增 public static final 修飾

1.3 使用 Enum 定義的示例


package org.springframework.http;

import org.springframework.lang.Nullable;

/**
 * Enumeration of HTTP status codes.
 *
 * <p>The HTTP status code series can be retrieved via {@link #series()}.
 *
 * @author Arjen Poutsma
 * @author Sebastien Deleuze
 * @author Brian Clozel
 * @since 3.0
 * @see HttpStatus.Series
 * @see <a href="https://www.iana.org/assignments/http-status-codes">HTTP Status Code Registry</a>
 * @see <a href="https://en.wikipedia.org/wiki/List_of_HTTP_status_codes">List of HTTP status codes - Wikipedia</a>
 */
public enum HttpStatus {

	// 1xx Informational

	/**
	 * {@code 100 Continue}.
	 * @see <a href="https://tools.ietf.org/html/rfc7231#section-6.2.1">HTTP/1.1: Semantics and Content, section 6.2.1</a>
	 */
	CONTINUE(100, "Continue"),
	/**
	 * {@code 101 Switching Protocols}.
	 * @see <a href="https://tools.ietf.org/html/rfc7231#section-6.2.2">HTTP/1.1: Semantics and Content, section 6.2.2</a>
	 */
	SWITCHING_PROTOCOLS(101, "Switching Protocols"),
	/**
	 * {@code 102 Processing}.
	 * @see <a href="https://tools.ietf.org/html/rfc2518#section-10.1">WebDAV</a>
	 */
	PROCESSING(102, "Processing"),
	/**
	 * {@code 103 Checkpoint}.
	 * @see <a href="https://code.google.com/p/gears/wiki/ResumableHttpRequestsProposal">A proposal for supporting
	 * resumable POST/PUT HTTP requests in HTTP/1.0</a>
	 */
	CHECKPOINT(103, "Checkpoint"),

	// 2xx Success

	/**
	 * {@code 200 OK}.
	 * @see <a href="https://tools.ietf.org/html/rfc7231#section-6.3.1">HTTP/1.1: Semantics and Content, section 6.3.1</a>
	 */
	OK(200, "OK"),
	/**
	 * {@code 201 Created}.
	 * @see <a href="https://tools.ietf.org/html/rfc7231#section-6.3.2">HTTP/1.1: Semantics and Content, section 6.3.2</a>
	 */
	CREATED(201, "Created"),
	/**
	 * {@code 202 Accepted}.
	 * @see <a href="https://tools.ietf.org/html/rfc7231#section-6.3.3">HTTP/1.1: Semantics and Content, section 6.3.3</a>
	 */
	ACCEPTED(202, "Accepted"),
	/**
	 * {@code 203 Non-Authoritative Information}.
	 * @see <a href="https://tools.ietf.org/html/rfc7231#section-6.3.4">HTTP/1.1: Semantics and Content, section 6.3.4</a>
	 */
	NON_AUTHORITATIVE_INFORMATION(203, "Non-Authoritative Information"),
	/**
	 * {@code 204 No Content}.
	 * @see <a href="https://tools.ietf.org/html/rfc7231#section-6.3.5">HTTP/1.1: Semantics and Content, section 6.3.5</a>
	 */
	NO_CONTENT(204, "No Content"),
	/**
	 * {@code 205 Reset Content}.
	 * @see <a href="https://tools.ietf.org/html/rfc7231#section-6.3.6">HTTP/1.1: Semantics and Content, section 6.3.6</a>
	 */
	RESET_CONTENT(205, "Reset Content"),
	/**
	 * {@code 206 Partial Content}.
	 * @see <a href="https://tools.ietf.org/html/rfc7233#section-4.1">HTTP/1.1: Range Requests, section 4.1</a>
	 */
	PARTIAL_CONTENT(206, "Partial Content"),
	/**
	 * {@code 207 Multi-Status}.
	 * @see <a href="https://tools.ietf.org/html/rfc4918#section-13">WebDAV</a>
	 */
	MULTI_STATUS(207, "Multi-Status"),
	/**
	 * {@code 208 Already Reported}.
	 * @see <a href="https://tools.ietf.org/html/rfc5842#section-7.1">WebDAV Binding Extensions</a>
	 */
	ALREADY_REPORTED(208, "Already Reported"),
	/**
	 * {@code 226 IM Used}.
	 * @see <a href="https://tools.ietf.org/html/rfc3229#section-10.4.1">Delta encoding in HTTP</a>
	 */
	IM_USED(226, "IM Used"),

	// 3xx Redirection

	/**
	 * {@code 300 Multiple Choices}.
	 * @see <a href="https://tools.ietf.org/html/rfc7231#section-6.4.1">HTTP/1.1: Semantics and Content, section 6.4.1</a>
	 */
	MULTIPLE_CHOICES(300, "Multiple Choices"),
	/**
	 * {@code 301 Moved Permanently}.
	 * @see <a href="https://tools.ietf.org/html/rfc7231#section-6.4.2">HTTP/1.1: Semantics and Content, section 6.4.2</a>
	 */
	MOVED_PERMANENTLY(301, "Moved Permanently"),
	/**
	 * {@code 302 Found}.
	 * @see <a href="https://tools.ietf.org/html/rfc7231#section-6.4.3">HTTP/1.1: Semantics and Content, section 6.4.3</a>
	 */
	FOUND(302, "Found"),
	/**
	 * {@code 302 Moved Temporarily}.
	 * @see <a href="https://tools.ietf.org/html/rfc1945#section-9.3">HTTP/1.0, section 9.3</a>
	 * @deprecated in favor of {@link #FOUND} which will be returned from {@code HttpStatus.valueOf(302)}
	 */
	@Deprecated
	MOVED_TEMPORARILY(302, "Moved Temporarily"),
	/**
	 * {@code 303 See Other}.
	 * @see <a href="https://tools.ietf.org/html/rfc7231#section-6.4.4">HTTP/1.1: Semantics and Content, section 6.4.4</a>
	 */
	SEE_OTHER(303, "See Other"),
	/**
	 * {@code 304 Not Modified}.
	 * @see <a href="https://tools.ietf.org/html/rfc7232#section-4.1">HTTP/1.1: Conditional Requests, section 4.1</a>
	 */
	NOT_MODIFIED(304, "Not Modified"),
	/**
	 * {@code 305 Use Proxy}.
	 * @see <a href="https://tools.ietf.org/html/rfc7231#section-6.4.5">HTTP/1.1: Semantics and Content, section 6.4.5</a>
	 * @deprecated due to security concerns regarding in-band configuration of a proxy
	 */
	@Deprecated
	USE_PROXY(305, "Use Proxy"),
	/**
	 * {@code 307 Temporary Redirect}.
	 * @see <a href="https://tools.ietf.org/html/rfc7231#section-6.4.7">HTTP/1.1: Semantics and Content, section 6.4.7</a>
	 */
	TEMPORARY_REDIRECT(307, "Temporary Redirect"),
	/**
	 * {@code 308 Permanent Redirect}.
	 * @see <a href="https://tools.ietf.org/html/rfc7238">RFC 7238</a>
	 */
	PERMANENT_REDIRECT(308, "Permanent Redirect"),

	// --- 4xx Client Error ---

	/**
	 * {@code 400 Bad Request}.
	 * @see <a href="https://tools.ietf.org/html/rfc7231#section-6.5.1">HTTP/1.1: Semantics and Content, section 6.5.1</a>
	 */
	BAD_REQUEST(400, "Bad Request"),
	/**
	 * {@code 401 Unauthorized}.
	 * @see <a href="https://tools.ietf.org/html/rfc7235#section-3.1">HTTP/1.1: Authentication, section 3.1</a>
	 */
	UNAUTHORIZED(401, "Unauthorized"),
	/**
	 * {@code 402 Payment Required}.
	 * @see <a href="https://tools.ietf.org/html/rfc7231#section-6.5.2">HTTP/1.1: Semantics and Content, section 6.5.2</a>
	 */
	PAYMENT_REQUIRED(402, "Payment Required"),
	/**
	 * {@code 403 Forbidden}.
	 * @see <a href="https://tools.ietf.org/html/rfc7231#section-6.5.3">HTTP/1.1: Semantics and Content, section 6.5.3</a>
	 */
	FORBIDDEN(403, "Forbidden"),
	/**
	 * {@code 404 Not Found}.
	 * @see <a href="https://tools.ietf.org/html/rfc7231#section-6.5.4">HTTP/1.1: Semantics and Content, section 6.5.4</a>
	 */
	NOT_FOUND(404, "Not Found"),
	/**
	 * {@code 405 Method Not Allowed}.
	 * @see <a href="https://tools.ietf.org/html/rfc7231#section-6.5.5">HTTP/1.1: Semantics and Content, section 6.5.5</a>
	 */
	METHOD_NOT_ALLOWED(405, "Method Not Allowed"),
	/**
	 * {@code 406 Not Acceptable}.
	 * @see <a href="https://tools.ietf.org/html/rfc7231#section-6.5.6">HTTP/1.1: Semantics and Content, section 6.5.6</a>
	 */
	NOT_ACCEPTABLE(406, "Not Acceptable"),
	/**
	 * {@code 407 Proxy Authentication Required}.
	 * @see <a href="https://tools.ietf.org/html/rfc7235#section-3.2">HTTP/1.1: Authentication, section 3.2</a>
	 */
	PROXY_AUTHENTICATION_REQUIRED(407, "Proxy Authentication Required"),
	/**
	 * {@code 408 Request Timeout}.
	 * @see <a href="https://tools.ietf.org/html/rfc7231#section-6.5.7">HTTP/1.1: Semantics and Content, section 6.5.7</a>
	 */
	REQUEST_TIMEOUT(408, "Request Timeout"),
	/**
	 * {@code 409 Conflict}.
	 * @see <a href="https://tools.ietf.org/html/rfc7231#section-6.5.8">HTTP/1.1: Semantics and Content, section 6.5.8</a>
	 */
	CONFLICT(409, "Conflict"),
	/**
	 * {@code 410 Gone}.
	 * @see <a href="https://tools.ietf.org/html/rfc7231#section-6.5.9">
	 *     HTTP/1.1: Semantics and Content, section 6.5.9</a>
	 */
	GONE(410, "Gone"),
	/**
	 * {@code 411 Length Required}.
	 * @see <a href="https://tools.ietf.org/html/rfc7231#section-6.5.10">
	 *     HTTP/1.1: Semantics and Content, section 6.5.10</a>
	 */
	LENGTH_REQUIRED(411, "Length Required"),
	/**
	 * {@code 412 Precondition failed}.
	 * @see <a href="https://tools.ietf.org/html/rfc7232#section-4.2">
	 *     HTTP/1.1: Conditional Requests, section 4.2</a>
	 */
	PRECONDITION_FAILED(412, "Precondition Failed"),
	/**
	 * {@code 413 Payload Too Large}.
	 * @since 4.1
	 * @see <a href="https://tools.ietf.org/html/rfc7231#section-6.5.11">
	 *     HTTP/1.1: Semantics and Content, section 6.5.11</a>
	 */
	PAYLOAD_TOO_LARGE(413, "Payload Too Large"),
	/**
	 * {@code 413 Request Entity Too Large}.
	 * @see <a href="https://tools.ietf.org/html/rfc2616#section-10.4.14">HTTP/1.1, section 10.4.14</a>
	 * @deprecated in favor of {@link #PAYLOAD_TOO_LARGE} which will be
	 * returned from {@code HttpStatus.valueOf(413)}
	 */
	@Deprecated
	REQUEST_ENTITY_TOO_LARGE(413, "Request Entity Too Large"),
	/**
	 * {@code 414 URI Too Long}.
	 * @since 4.1
	 * @see <a href="https://tools.ietf.org/html/rfc7231#section-6.5.12">
	 *     HTTP/1.1: Semantics and Content, section 6.5.12</a>
	 */
	URI_TOO_LONG(414, "URI Too Long"),
	/**
	 * {@code 414 Request-URI Too Long}.
	 * @see <a href="https://tools.ietf.org/html/rfc2616#section-10.4.15">HTTP/1.1, section 10.4.15</a>
	 * @deprecated in favor of {@link #URI_TOO_LONG} which will be returned from {@code HttpStatus.valueOf(414)}
	 */
	@Deprecated
	REQUEST_URI_TOO_LONG(414, "Request-URI Too Long"),
	/**
	 * {@code 415 Unsupported Media Type}.
	 * @see <a href="https://tools.ietf.org/html/rfc7231#section-6.5.13">
	 *     HTTP/1.1: Semantics and Content, section 6.5.13</a>
	 */
	UNSUPPORTED_MEDIA_TYPE(415, "Unsupported Media Type"),
	/**
	 * {@code 416 Requested Range Not Satisfiable}.
	 * @see <a href="https://tools.ietf.org/html/rfc7233#section-4.4">HTTP/1.1: Range Requests, section 4.4</a>
	 */
	REQUESTED_RANGE_NOT_SATISFIABLE(416, "Requested range not satisfiable"),
	/**
	 * {@code 417 Expectation Failed}.
	 * @see <a href="https://tools.ietf.org/html/rfc7231#section-6.5.14">
	 *     HTTP/1.1: Semantics and Content, section 6.5.14</a>
	 */
	EXPECTATION_FAILED(417, "Expectation Failed"),
	/**
	 * {@code 418 I'm a teapot}.
	 * @see <a href="https://tools.ietf.org/html/rfc2324#section-2.3.2">HTCPCP/1.0</a>
	 */
	I_AM_A_TEAPOT(418, "I'm a teapot"),
	/**
	 * @deprecated See
	 * <a href="https://tools.ietf.org/rfcdiff?difftype=--hwdiff&url2=draft-ietf-webdav-protocol-06.txt">
	 *     WebDAV Draft Changes</a>
	 */
	@Deprecated
	INSUFFICIENT_SPACE_ON_RESOURCE(419, "Insufficient Space On Resource"),
	/**
	 * @deprecated See
	 * <a href="https://tools.ietf.org/rfcdiff?difftype=--hwdiff&url2=draft-ietf-webdav-protocol-06.txt">
	 *     WebDAV Draft Changes</a>
	 */
	@Deprecated
	METHOD_FAILURE(420, "Method Failure"),
	/**
	 * @deprecated
	 * See <a href="https://tools.ietf.org/rfcdiff?difftype=--hwdiff&url2=draft-ietf-webdav-protocol-06.txt">
	 *     WebDAV Draft Changes</a>
	 */
	@Deprecated
	DESTINATION_LOCKED(421, "Destination Locked"),
	/**
	 * {@code 422 Unprocessable Entity}.
	 * @see <a href="https://tools.ietf.org/html/rfc4918#section-11.2">WebDAV</a>
	 */
	UNPROCESSABLE_ENTITY(422, "Unprocessable Entity"),
	/**
	 * {@code 423 Locked}.
	 * @see <a href="https://tools.ietf.org/html/rfc4918#section-11.3">WebDAV</a>
	 */
	LOCKED(423, "Locked"),
	/**
	 * {@code 424 Failed Dependency}.
	 * @see <a href="https://tools.ietf.org/html/rfc4918#section-11.4">WebDAV</a>
	 */
	FAILED_DEPENDENCY(424, "Failed Dependency"),
	/**
	 * {@code 425 Too Early}.
	 * @since 5.2
	 * @see <a href="https://tools.ietf.org/html/rfc8470">RFC 8470</a>
	 */
	TOO_EARLY(425, "Too Early"),
	/**
	 * {@code 426 Upgrade Required}.
	 * @see <a href="https://tools.ietf.org/html/rfc2817#section-6">Upgrading to TLS Within HTTP/1.1</a>
	 */
	UPGRADE_REQUIRED(426, "Upgrade Required"),
	/**
	 * {@code 428 Precondition Required}.
	 * @see <a href="https://tools.ietf.org/html/rfc6585#section-3">Additional HTTP Status Codes</a>
	 */
	PRECONDITION_REQUIRED(428, "Precondition Required"),
	/**
	 * {@code 429 Too Many Requests}.
	 * @see <a href="https://tools.ietf.org/html/rfc6585#section-4">Additional HTTP Status Codes</a>
	 */
	TOO_MANY_REQUESTS(429, "Too Many Requests"),
	/**
	 * {@code 431 Request Header Fields Too Large}.
	 * @see <a href="https://tools.ietf.org/html/rfc6585#section-5">Additional HTTP Status Codes</a>
	 */
	REQUEST_HEADER_FIELDS_TOO_LARGE(431, "Request Header Fields Too Large"),
	/**
	 * {@code 451 Unavailable For Legal Reasons}.
	 * @see <a href="https://tools.ietf.org/html/draft-ietf-httpbis-legally-restricted-status-04">
	 * An HTTP Status Code to Report Legal Obstacles</a>
	 * @since 4.3
	 */
	UNAVAILABLE_FOR_LEGAL_REASONS(451, "Unavailable For Legal Reasons"),

	// --- 5xx Server Error ---

	/**
	 * {@code 500 Internal Server Error}.
	 * @see <a href="https://tools.ietf.org/html/rfc7231#section-6.6.1">HTTP/1.1: Semantics and Content, section 6.6.1</a>
	 */
	INTERNAL_SERVER_ERROR(500, "Internal Server Error"),
	/**
	 * {@code 501 Not Implemented}.
	 * @see <a href="https://tools.ietf.org/html/rfc7231#section-6.6.2">HTTP/1.1: Semantics and Content, section 6.6.2</a>
	 */
	NOT_IMPLEMENTED(501, "Not Implemented"),
	/**
	 * {@code 502 Bad Gateway}.
	 * @see <a href="https://tools.ietf.org/html/rfc7231#section-6.6.3">HTTP/1.1: Semantics and Content, section 6.6.3</a>
	 */
	BAD_GATEWAY(502, "Bad Gateway"),
	/**
	 * {@code 503 Service Unavailable}.
	 * @see <a href="https://tools.ietf.org/html/rfc7231#section-6.6.4">HTTP/1.1: Semantics and Content, section 6.6.4</a>
	 */
	SERVICE_UNAVAILABLE(503, "Service Unavailable"),
	/**
	 * {@code 504 Gateway Timeout}.
	 * @see <a href="https://tools.ietf.org/html/rfc7231#section-6.6.5">HTTP/1.1: Semantics and Content, section 6.6.5</a>
	 */
	GATEWAY_TIMEOUT(504, "Gateway Timeout"),
	/**
	 * {@code 505 HTTP Version Not Supported}.
	 * @see <a href="https://tools.ietf.org/html/rfc7231#section-6.6.6">HTTP/1.1: Semantics and Content, section 6.6.6</a>
	 */
	HTTP_VERSION_NOT_SUPPORTED(505, "HTTP Version not supported"),
	/**
	 * {@code 506 Variant Also Negotiates}
	 * @see <a href="https://tools.ietf.org/html/rfc2295#section-8.1">Transparent Content Negotiation</a>
	 */
	VARIANT_ALSO_NEGOTIATES(506, "Variant Also Negotiates"),
	/**
	 * {@code 507 Insufficient Storage}
	 * @see <a href="https://tools.ietf.org/html/rfc4918#section-11.5">WebDAV</a>
	 */
	INSUFFICIENT_STORAGE(507, "Insufficient Storage"),
	/**
	 * {@code 508 Loop Detected}
	 * @see <a href="https://tools.ietf.org/html/rfc5842#section-7.2">WebDAV Binding Extensions</a>
 	 */
	LOOP_DETECTED(508, "Loop Detected"),
	/**
	 * {@code 509 Bandwidth Limit Exceeded}
 	 */
	BANDWIDTH_LIMIT_EXCEEDED(509, "Bandwidth Limit Exceeded"),
	/**
	 * {@code 510 Not Extended}
	 * @see <a href="https://tools.ietf.org/html/rfc2774#section-7">HTTP Extension Framework</a>
	 */
	NOT_EXTENDED(510, "Not Extended"),
	/**
	 * {@code 511 Network Authentication Required}.
	 * @see <a href="https://tools.ietf.org/html/rfc6585#section-6">Additional HTTP Status Codes</a>
	 */
	NETWORK_AUTHENTICATION_REQUIRED(511, "Network Authentication Required");


	private final int value;

	private final String reasonPhrase;


	HttpStatus(int value, String reasonPhrase) {
		this.value = value;
		this.reasonPhrase = reasonPhrase;
	}


	/**
	 * Return the integer value of this status code.
	 */
	public int value() {
		return this.value;
	}

	/**
	 * Return the reason phrase of this status code.
	 */
	public String getReasonPhrase() {
		return this.reasonPhrase;
	}

	/**
	 * Return the HTTP status series of this status code.
	 * @see HttpStatus.Series
	 */
	public Series series() {
		return Series.valueOf(this);
	}

	/**
	 * Whether this status code is in the HTTP series
	 * {@link org.springframework.http.HttpStatus.Series#INFORMATIONAL}.
	 * This is a shortcut for checking the value of {@link #series()}.
	 * @since 4.0
	 * @see #series()
	 */
	public boolean is1xxInformational() {
		return (series() == Series.INFORMATIONAL);
	}

	/**
	 * Whether this status code is in the HTTP series
	 * {@link org.springframework.http.HttpStatus.Series#SUCCESSFUL}.
	 * This is a shortcut for checking the value of {@link #series()}.
	 * @since 4.0
	 * @see #series()
	 */
	public boolean is2xxSuccessful() {
		return (series() == Series.SUCCESSFUL);
	}

	/**
	 * Whether this status code is in the HTTP series
	 * {@link org.springframework.http.HttpStatus.Series#REDIRECTION}.
	 * This is a shortcut for checking the value of {@link #series()}.
	 * @since 4.0
	 * @see #series()
	 */
	public boolean is3xxRedirection() {
		return (series() == Series.REDIRECTION);
	}

	/**
	 * Whether this status code is in the HTTP series
	 * {@link org.springframework.http.HttpStatus.Series#CLIENT_ERROR}.
	 * This is a shortcut for checking the value of {@link #series()}.
	 * @since 4.0
	 * @see #series()
	 */
	public boolean is4xxClientError() {
		return (series() == Series.CLIENT_ERROR);
	}

	/**
	 * Whether this status code is in the HTTP series
	 * {@link org.springframework.http.HttpStatus.Series#SERVER_ERROR}.
	 * This is a shortcut for checking the value of {@link #series()}.
	 * @since 4.0
	 * @see #series()
	 */
	public boolean is5xxServerError() {
		return (series() == Series.SERVER_ERROR);
	}

	/**
	 * Whether this status code is in the HTTP series
	 * {@link org.springframework.http.HttpStatus.Series#CLIENT_ERROR} or
	 * {@link org.springframework.http.HttpStatus.Series#SERVER_ERROR}.
	 * This is a shortcut for checking the value of {@link #series()}.
	 * @since 5.0
	 * @see #is4xxClientError()
	 * @see #is5xxServerError()
	 */
	public boolean isError() {
		return (is4xxClientError() || is5xxServerError());
	}

	/**
	 * Return a string representation of this status code.
	 */
	@Override
	public String toString() {
		return this.value + " " + name();
	}


	/**
	 * Return the enum constant of this type with the specified numeric value.
	 * @param statusCode the numeric value of the enum to be returned
	 * @return the enum constant with the specified numeric value
	 * @throws IllegalArgumentException if this enum has no constant for the specified numeric value
	 */
	public static HttpStatus valueOf(int statusCode) {
		HttpStatus status = resolve(statusCode);
		if (status == null) {
			throw new IllegalArgumentException("No matching constant for [" + statusCode + "]");
		}
		return status;
	}

	/**
	 * Resolve the given status code to an {@code HttpStatus}, if possible.
	 * @param statusCode the HTTP status code (potentially non-standard)
	 * @return the corresponding {@code HttpStatus}, or {@code null} if not found
	 * @since 5.0
	 */
	@Nullable
	public static HttpStatus resolve(int statusCode) {
		for (HttpStatus status : values()) {
			if (status.value == statusCode) {
				return status;
			}
		}
		return null;
	}


	/**
	 * Enumeration of HTTP status series.
	 * <p>Retrievable via {@link HttpStatus#series()}.
	 */
	public enum Series {

		INFORMATIONAL(1),
		SUCCESSFUL(2),
		REDIRECTION(3),
		CLIENT_ERROR(4),
		SERVER_ERROR(5);

		private final int value;

		Series(int value) {
			this.value = value;
		}

		/**
		 * Return the integer value of this status series. Ranges from 1 to 5.
		 */
		public int value() {
			return this.value;
		}

		/**
		 * Return the enum constant of this type with the corresponding series.
		 * @param status a standard HTTP status enum value
		 * @return the enum constant of this type with the corresponding series
		 * @throws IllegalArgumentException if this enum has no corresponding constant
		 */
		public static Series valueOf(HttpStatus status) {
			return valueOf(status.value);
		}

		/**
		 * Return the enum constant of this type with the corresponding series.
		 * @param statusCode the HTTP status code (potentially non-standard)
		 * @return the enum constant of this type with the corresponding series
		 * @throws IllegalArgumentException if this enum has no corresponding constant
		 */
		public static Series valueOf(int statusCode) {
			Series series = resolve(statusCode);
			if (series == null) {
				throw new IllegalArgumentException("No matching constant for [" + statusCode + "]");
			}
			return series;
		}

		/**
		 * Resolve the given status code to an {@code HttpStatus.Series}, if possible.
		 * @param statusCode the HTTP status code (potentially non-standard)
		 * @return the corresponding {@code Series}, or {@code null} if not found
		 * @since 5.1.3
		 */
		@Nullable
		public static Series resolve(int statusCode) {
			int seriesCode = statusCode / 100;
			for (Series series : values()) {
				if (series.value == seriesCode) {
					return series;
				}
			}
			return null;
		}
	}

}

1.4 列舉類

列舉類的主要方法：
values()方法：返回列舉型別的物件陣列。該方法可以很方便地遍歷所有的列舉值。
valueOf(String str)：可以把一個字串轉為對應的列舉類物件。要求字串必須是列舉類物件的“名字”。如不是，會有執行時異常。

1.5 列舉的方法

1.6 實現介面的列舉類

和普通 Java 類一樣，列舉類可以實現一個或多個介面。若需要每個列舉值在呼叫實現的介面方法呈現出不同的行為方式, 則可以讓每個列舉值分別來實現該方法。

二、註解Annotation

從 JDK 5.0 開始, Java 增加了對元資料(MetaData) 的支援, 也就是 Annotation(註解)。Annotation 其實就是程式碼裡的特殊標記, 這些標記可以在編譯, 類載入, 執行時被讀取, 並執行相應的處理. 通過使用 Annotation, 程式設計師可以在不改變原有邏輯的情況下, 在原始檔中嵌入一些補充資訊。Annotation 可以像修飾符一樣被使用, 可用於修飾包,類, 構造器, 方法, 成員變數, 引數, 區域性變數的宣告, 這些資訊被儲存在 Annotation 的 “name=value” 對中。Annotation 能被用來為程式元素(類, 方法, 成員變數等) 設定元資料。

2.1 基本的 Annotation

使用 Annotation 時要在其前面增加 @ 符號, 並把該 Annotation 當成一個修飾符使用。用於修飾它支援的程式元素
三個基本的 Annotation:
@Override: 限定重寫父類方法, 該註釋只能用於方法
@Deprecated: 用於表示某個程式元素(類, 方法等)已過時
@SuppressWarnings: 抑制編譯器警告

2.2 自定義 Annotation

定義新的 Annotation 型別使用@interface關鍵字。
Annotation 的成員變數在 Annotation 定義中以無引數方法的形式來宣告. 其方法名和返回值定義了該成員的名字和型別。
可以在定義 Annotation 的成員變數時為其指定初始值, 指定成員變數的初始值可使用 default 關鍵字

  public @interface MyAnnotation{
   String name() default "相逢何必曾相識";
  }

沒有成員定義的 Annotation 稱為標記; 包含成員變數的 Annotation 稱為元資料 Annotation。

2.3 提取 Annotation 資訊

JDK 5.0 在 java.lang.reflect 包下新增了 AnnotatedElement 介面, 該介面代表程式中可以接受註解的程式元素。
當一個 Annotation 型別被定義為執行時 Annotation 後, 該註釋才是執行時可見, 當 class 檔案被載入時儲存在 class 檔案中的 Annotation 才會被虛擬機器讀取。
程式可以呼叫 AnnotationElement 物件的如下方法來訪問 Annotation 資訊。

2.4 JDK 的元 Annotation

JDK 的元 Annotation 用於修飾其他 Annotation 定義；JDK5.0提供了專門在註解上的註解型別，分別是：
Retention
Target
Documented
Inherited

@Retention: 只能用於修飾一個 Annotation 定義, 用於指定該 Annotation 可以保留多長時間, @Rentention 包含一個 RetentionPolicy 型別的成員變數, 使用 @Rentention 時必須為該 value 成員變數指定值:
RetentionPolicy.SOURCE: 編譯器直接丟棄這種策略的註釋
RetentionPolicy.CLASS: 編譯器將把註釋記錄在 class 檔案中. 當執行 Java 程式時, JVM 不會保留註解。這是預設值
RetentionPolicy.RUNTIME:編譯器將把註釋記錄在 class 檔案中. 當執行 Java 程式時, JVM 會保留註釋. 程式可以通過反射獲取該註釋

@Target: 用於修飾 Annotation 定義, 用於指定被修飾的 Annotation 能用於修飾哪些程式元素. @Target 也包含一個名為 value 的成員變數.

@Documented: 用於指定被該元 Annotation 修飾的 Annotation 類將被 javadoc 工具提取成文件.
定義為Documented的註解必須設定Retention值為RUNTIME。

@Inherited: 被它修飾的 Annotation 將具有繼承性.如果某個類使用了被 @Inherited 修飾的 Annotation, 則其子類將自動具有該註解

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Java的列舉與註解

一、列舉類

1.1 列舉類的屬性

1.2 Enum列舉類

1.3 使用 Enum 定義的示例

1.4 列舉類

1.5 列舉的方法

1.6 實現介面的列舉類

二、註解Annotation

2.1 基本的 Annotation

2.2 自定義 Annotation

2.3 提取 Annotation 資訊

2.4 JDK 的元 Annotation

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Java的列舉與註解

一、列舉類

1.1 列舉類的屬性

1.2 Enum列舉類

1.3 使用 Enum 定義的示例

1.4 列舉類

1.5 列舉的方法

1.6 實現介面的列舉類

二、註解Annotation

2.1 基本的 Annotation

2.2 自定義 Annotation

2.3 提取 Annotation 資訊

2.4 JDK 的元 Annotation

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