为何在Java的世界里Spring一家独大

1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
/**
 * Interface for a resource descriptor that abstracts from the actual
 * type of underlying resource, such as a file or class path resource.
 *
 * <p>An InputStream can be opened for every resource if it exists in
 * physical form, but a URL or File handle can just be returned for
 * certain resources. The actual behavior is implementation-specific.
 *
 * @author Juergen Hoeller
 * @since 28.12.2003
 * @see #getInputStream()
 * @see #getURL()
 * @see #getURI()
 * @see #getFile()
 * @see WritableResource
 * @see ContextResource
 * @see UrlResource
 * @see FileUrlResource
 * @see FileSystemResource
 * @see ClassPathResource
 * @see ByteArrayResource
 * @see InputStreamResource
 */
public interface Resource extends InputStreamSource {

	/**
	 * Determine whether this resource actually exists in physical form.
	 * <p>This method performs a definitive existence check, whereas the
	 * existence of a {@code Resource} handle only guarantees a valid
	 * descriptor handle.
	 */
	boolean exists();

	/**
	 * Indicate whether non-empty contents of this resource can be read via
	 * {@link #getInputStream()}.
	 * <p>Will be {@code true} for typical resource descriptors that exist
	 * since it strictly implies {@link #exists()} semantics as of 5.1.
	 * Note that actual content reading may still fail when attempted.
	 * However, a value of {@code false} is a definitive indication
	 * that the resource content cannot be read.
	 * @see #getInputStream()
	 * @see #exists()
	 */
	default boolean isReadable() {
		return exists();
	}

	/**
	 * Indicate whether this resource represents a handle with an open stream.
	 * If {@code true}, the InputStream cannot be read multiple times,
	 * and must be read and closed to avoid resource leaks.
	 * <p>Will be {@code false} for typical resource descriptors.
	 */
	default boolean isOpen() {
		return false;
	}

	/**
	 * Determine whether this resource represents a file in a file system.
	 * A value of {@code true} strongly suggests (but does not guarantee)
	 * that a {@link #getFile()} call will succeed.
	 * <p>This is conservatively {@code false} by default.
	 * @since 5.0
	 * @see #getFile()
	 */
	default boolean isFile() {
		return false;
	}

	/**
	 * Return a URL handle for this resource.
	 * @throws IOException if the resource cannot be resolved as URL,
	 * i.e. if the resource is not available as descriptor
	 */
	URL getURL() throws IOException;

	/**
	 * Return a URI handle for this resource.
	 * @throws IOException if the resource cannot be resolved as URI,
	 * i.e. if the resource is not available as descriptor
	 * @since 2.5
	 */
	URI getURI() throws IOException;

	/**
	 * Return a File handle for this resource.
	 * @throws java.io.FileNotFoundException if the resource cannot be resolved as
	 * absolute file path, i.e. if the resource is not available in a file system
	 * @throws IOException in case of general resolution/reading failures
	 * @see #getInputStream()
	 */
	File getFile() throws IOException;

	/**
	 * Return a {@link ReadableByteChannel}.
	 * <p>It is expected that each call creates a <i>fresh</i> channel.
	 * <p>The default implementation returns {@link Channels#newChannel(InputStream)}
	 * with the result of {@link #getInputStream()}.
	 * @return the byte channel for the underlying resource (must not be {@code null})
	 * @throws java.io.FileNotFoundException if the underlying resource doesn't exist
	 * @throws IOException if the content channel could not be opened
	 * @since 5.0
	 * @see #getInputStream()
	 */
	default ReadableByteChannel readableChannel() throws IOException {
		return Channels.newChannel(getInputStream());
	}

	/**
	 * Determine the content length for this resource.
	 * @throws IOException if the resource cannot be resolved
	 * (in the file system or as some other known physical resource type)
	 */
	long contentLength() throws IOException;

	/**
	 * Determine the last-modified timestamp for this resource.
	 * @throws IOException if the resource cannot be resolved
	 * (in the file system or as some other known physical resource type)
	 */
	long lastModified() throws IOException;

	/**
	 * Create a resource relative to this resource.
	 * @param relativePath the relative path (relative to this resource)
	 * @return the resource handle for the relative resource
	 * @throws IOException if the relative resource cannot be determined
	 */
	Resource createRelative(String relativePath) throws IOException;

	/**
	 * Determine a filename for this resource, i.e. typically the last
	 * part of the path: for example, "myfile.txt".
	 * <p>Returns {@code null} if this type of resource does not
	 * have a filename.
	 */
	@Nullable
	String getFilename();

	/**
	 * Return a description for this resource,
	 * to be used for error output when working with the resource.
	 * <p>Implementations are also encouraged to return this value
	 * from their {@code toString} method.
	 * @see Object#toString()
	 */
	String getDescription();
}