Introduce Resource::getContentAsString

This commit introduces the getContentAsString method to Resource,
returning the string contents of the resource.

Closes gh-24651

Author: derrick-anderson

spring-core/src/main/java/org/springframework/core/io/AbstractFileResolvingResource.java

@@ -26,7 +26,10 @@
 import java.net.URLConnection;
 import java.nio.channels.FileChannel;
 import java.nio.channels.ReadableByteChannel;
+import java.nio.charset.Charset;
+import java.nio.file.Files;
 import java.nio.file.NoSuchFileException;
+import java.nio.file.Paths;
 import java.nio.file.StandardOpenOption;
 import java.util.jar.JarEntry;
 
@@ -320,6 +323,39 @@ protected void customizeConnection(URLConnection con) throws IOException {
 	protected void customizeConnection(HttpURLConnection con) throws IOException {
 	}
 
+	/**
+	 * This implementation returns the contents of a file as a string using the
+	 * system default Charset. Provided the resource exists and the context has
+	 * access to it, the contents will be returned as a single string with line
+	 * feed characters retained.
+	 * @return the contents of the requested file as a {@code String}.
+	 * @throws FileNotFoundException in the event the file path is invalid.
+	 * @throws IOException if the file can not be read or cannot be serialzied.
+	 */
+	@Override
+	public String getContentAsString() throws IOException {
+
+		if( !exists() ) {
+			throw new FileNotFoundException(getDescription() + " cannot be found.");
+		}
+		if ( !isReadable() ) {
+			throw new IOException(getDescription() + " cannot be opened for reading.");
+		}
+		return new String(Files.readAllBytes(Paths.get(getFile().getAbsolutePath())), Charset.defaultCharset());
+	}
+
+	@Override
+	public String getContentAsString(Charset charset) throws IOException {
+
+		if( !exists() ) {
+			throw new FileNotFoundException(getDescription() + " cannot be found.");
+		}
+		if ( !isReadable() ) {
+			throw new IOException(getDescription() + " cannot be opened for reading.");
+		}
+		return new String(Files.readAllBytes(Paths.get(getFile().getAbsolutePath())), charset);
+
+	}
 
 	/**
 	 * Inner delegate class, avoiding a hard JBoss VFS API dependency at runtime.

spring-core/src/main/java/org/springframework/core/io/Resource.java

@@ -17,12 +17,14 @@
 package org.springframework.core.io;
 
 import java.io.File;
+import java.io.FileNotFoundException;
 import java.io.IOException;
 import java.io.InputStream;
 import java.net.URI;
 import java.net.URL;
 import java.nio.channels.Channels;
 import java.nio.channels.ReadableByteChannel;
+import java.nio.charset.Charset;
 
 import org.springframework.lang.Nullable;
 
@@ -176,4 +178,41 @@ default ReadableByteChannel readableChannel() throws IOException {
 	 */
 	String getDescription();
 
+	/**
+	 * 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()
+	 */
+
+	/**
+	 * Returns the contents of a file as a string using the system default Charset.
+	 * <p>The default implementation returns a {@link Object#toString()} representation of the resource.
+	 * @return the contents of the requested file as a {@code String}.
+	 * @throws FileNotFoundException in the event the file path is invalid.
+	 * @throws IOException if the file can not be read or cannot be accessed.
+	 * @since 5.2.5
+	 */
+	default String getContentAsString() throws IOException{
+		return toString();
+	}
+
+	/**
+	 * Returns the contents of a file as a string using the specified Charset.
+	 * <p>The default implementation returns a {@link Object#toString()} representation of the resource.
+	 * @param charset the {@code Charset} to use to deserialize the content. Defaults to system default.
+	 * @return the contents of the requested file as a {@code String}.
+	 * @throws FileNotFoundException in the event the file path is invalid.
+	 * @throws IOException if the file can not be read or cannot be accessed.
+	 * @since 5.2.5
+	 */
+	default String getContentAsString(Charset charset) throws IOException{
+		return toString();
+	}
+
 }

spring-core/src/test/java/org/springframework/core/io/ResourceTests.java

@@ -456,4 +456,25 @@ public String getDescription() {
 
 	}
 
+	@Test
+	void getContentAsString_givenValidFile_ShouldReturnFileContent() throws IOException {
+		String expectedString = "<?xml version=\"1.0\" encoding=\"UTF-8\"?>\n"
+				+ "<!DOCTYPE properties SYSTEM \"http://java.sun.com/dtd/properties.dtd\">\n"
+				+ "<properties version=\"1.0\">\n"
+				+ "\t<entry key=\"foo\">bar</entry>\n"
+				+ "</properties>";
+
+		String fileDirString =
+				new ClassPathResource("org/springframework/core/io/example.xml").getContentAsString();
+		assertThat(fileDirString).isNotBlank();
+		assertThat(fileDirString).isEqualTo(expectedString);
+	}
+
+	@Test
+	void getContentAsString_givenAnInvalidFile_ShouldThrowFileNotFoundException(){
+		assertThatExceptionOfType(FileNotFoundException.class)
+				.isThrownBy(new ClassPathResource("nonExistantFile")::getContentAsString);
+
+	}
+
 }

spring-core/src/test/resources/org/springframework/core/io/example.xml

@@ -2,5 +2,4 @@
 <!DOCTYPE properties SYSTEM "http://java.sun.com/dtd/properties.dtd">
 <properties version="1.0">
 	<entry key="foo">bar</entry>
-</properties>
-
+</properties>