spring SizeCalculatingEntryWriter 源码

springboot SizeCalculatingEntryWriter 代码

文件路径：/spring-boot-project/spring-boot-tools/spring-boot-loader-tools/src/main/java/org/springframework/boot/loader/tools/SizeCalculatingEntryWriter.java

/*
 * Copyright 2012-2022 the original author or authors.
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *      https://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

package org.springframework.boot.loader.tools;

import java.io.ByteArrayInputStream;
import java.io.ByteArrayOutputStream;
import java.io.File;
import java.io.FileInputStream;
import java.io.FileNotFoundException;
import java.io.FileOutputStream;
import java.io.IOException;
import java.io.InputStream;
import java.io.OutputStream;

import org.springframework.util.StreamUtils;

/**
 * {@link EntryWriter} that always provides size information.
 *
 * @author Phillip Webb
 */
final class SizeCalculatingEntryWriter implements EntryWriter {

	static final int THRESHOLD = 1024 * 20;

	private final Object content;

	private final int size;

	private SizeCalculatingEntryWriter(EntryWriter entryWriter) throws IOException {
		SizeCalculatingOutputStream outputStream = new SizeCalculatingOutputStream();
		try {
			entryWriter.write(outputStream);
		}
		finally {
			outputStream.close();
		}
		this.content = outputStream.getContent();
		this.size = outputStream.getSize();
	}

	@Override
	public void write(OutputStream outputStream) throws IOException {
		InputStream inputStream = getContentInputStream();
		copy(inputStream, outputStream);
	}

	private InputStream getContentInputStream() throws FileNotFoundException {
		if (this.content instanceof File file) {
			return new FileInputStream(file);
		}
		return new ByteArrayInputStream((byte[]) this.content);
	}

	private void copy(InputStream inputStream, OutputStream outputStream) throws IOException {
		try {
			StreamUtils.copy(inputStream, outputStream);
		}
		finally {
			inputStream.close();
		}
	}

	@Override
	public int size() {
		return this.size;
	}

	static EntryWriter get(EntryWriter entryWriter) throws IOException {
		if (entryWriter == null || entryWriter.size() != -1) {
			return entryWriter;
		}
		return new SizeCalculatingEntryWriter(entryWriter);
	}

	/**
	 * {@link OutputStream} to calculate the size and allow content to be written again.
	 */
	private static class SizeCalculatingOutputStream extends OutputStream {

		private int size = 0;

		private File tempFile;

		private OutputStream outputStream;

		SizeCalculatingOutputStream() {
			this.outputStream = new ByteArrayOutputStream();
		}

		@Override
		public void write(int b) throws IOException {
			write(new byte[] { (byte) b }, 0, 1);
		}

		@Override
		public void write(byte[] b, int off, int len) throws IOException {
			int updatedSize = this.size + len;
			if (updatedSize > THRESHOLD && this.outputStream instanceof ByteArrayOutputStream byteArrayOutputStream) {
				this.outputStream = convertToFileOutputStream(byteArrayOutputStream);
			}
			this.outputStream.write(b, off, len);
			this.size = updatedSize;
		}

		private OutputStream convertToFileOutputStream(ByteArrayOutputStream byteArrayOutputStream) throws IOException {
			initializeTempFile();
			FileOutputStream fileOutputStream = new FileOutputStream(this.tempFile);
			StreamUtils.copy(byteArrayOutputStream.toByteArray(), fileOutputStream);
			return fileOutputStream;
		}

		private void initializeTempFile() throws IOException {
			if (this.tempFile == null) {
				this.tempFile = File.createTempFile("springboot-", "-entrycontent");
				this.tempFile.deleteOnExit();
			}
		}

		@Override
		public void close() throws IOException {
			this.outputStream.close();
		}

		Object getContent() {
			return (this.outputStream instanceof ByteArrayOutputStream byteArrayOutputStream)
					? byteArrayOutputStream.toByteArray() : this.tempFile;
		}

		int getSize() {
			return this.size;
		}

	}

}

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