001/* 002 * Copyright (C) 2022 - 2024, the original author or authors. 003 * 004 * Licensed under the Apache License, Version 2.0 (the "License"); 005 * you may not use this file except in compliance with the License. 006 * You may obtain a copy of the License at 007 * 008 * http://www.apache.org/licenses/LICENSE-2.0 009 * 010 * Unless required by applicable law or agreed to in writing, software 011 * distributed under the License is distributed on an "AS IS" BASIS, 012 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. 013 * See the License for the specific language governing permissions and 014 * limitations under the License. 015 */ 016package io.github.ascopes.jct.diagnostics; 017 018import static java.util.Objects.requireNonNull; 019 020import java.io.IOException; 021import java.io.OutputStream; 022import java.io.OutputStreamWriter; 023import java.io.Writer; 024import java.nio.charset.Charset; 025import java.util.concurrent.locks.Lock; 026import java.util.concurrent.locks.ReentrantLock; 027import org.apiguardian.api.API; 028import org.apiguardian.api.API.Status; 029 030/** 031 * A writer that wraps an output stream and also writes any content to an in-memory buffer. 032 * 033 * <p>This is thread-safe. 034 * 035 * @author Ashley Scopes 036 * @since 0.0.1 037 */ 038@API(since = "0.0.1", status = Status.STABLE) 039public final class TeeWriter extends Writer { 040 041 private final Lock lock; 042 043 private volatile boolean closed; 044 045 private final Writer writer; 046 047 // We use a StringBuilder and manually synchronise it rather than 048 // a string buffer, as we want to manually synchronise the builder 049 // and the delegated output writer at the same time. 050 private final StringBuilder builder; 051 052 /** 053 * Initialise the writer. 054 * 055 * @param writer the underlying writer to "tee" to. 056 */ 057 public TeeWriter(Writer writer) { 058 lock = new ReentrantLock(); 059 closed = false; 060 061 this.writer = requireNonNull(writer, "writer"); 062 builder = new StringBuilder(); 063 builder.ensureCapacity(64); 064 } 065 066 @Override 067 public void close() throws IOException { 068 // release to set and acquire to check ensures in-order operations to prevent 069 // a very minute chance of a race condition. 070 lock.lock(); 071 try { 072 if (!closed) { 073 closed = true; 074 builder.trimToSize(); 075 writer.flush(); 076 writer.close(); 077 } 078 } finally { 079 lock.unlock(); 080 } 081 } 082 083 @Override 084 public void flush() throws IOException { 085 lock.lock(); 086 try { 087 ensureOpen(); 088 writer.flush(); 089 } finally { 090 lock.unlock(); 091 } 092 } 093 094 /** 095 * Get the content of the internal buffer. 096 * 097 * @return the content. 098 * @since 0.2.1 099 */ 100 @API(since = "0.2.1", status = Status.STABLE) 101 public String getContent() { 102 lock.lock(); 103 try { 104 return builder.toString(); 105 } finally { 106 lock.unlock(); 107 } 108 } 109 110 /** 111 * Get the content of the internal buffer. 112 * 113 * <p>This calls {@link #getContent()} internally as of 0.2.1. 114 * 115 * @return the content. 116 */ 117 @Override 118 public String toString() { 119 return getContent(); 120 } 121 122 @Override 123 public void write(char[] buffer, int offset, int length) throws IOException { 124 lock.lock(); 125 try { 126 ensureOpen(); 127 128 writer.write(buffer, offset, length); 129 // Only append to the buffer once we know that the writing 130 // operation has completed. 131 builder.append(buffer, offset, length); 132 } finally { 133 lock.unlock(); 134 } 135 } 136 137 private void ensureOpen() throws IOException { 138 if (closed) { 139 throw new IOException("TeeWriter is closed"); 140 } 141 } 142 143 /** 144 * Create a tee writer for the given output stream. 145 * 146 * <p>Remember you may need to manually flush the tee writer for all contents to be committed to 147 * the output stream. 148 * 149 * @param outputStream the output stream. 150 * @param charset the charset. 151 * @return the Tee Writer. 152 * @since 0.2.1 153 */ 154 @API(since = "0.2.1", status = Status.STABLE) 155 public static TeeWriter wrapOutputStream(OutputStream outputStream, Charset charset) { 156 requireNonNull(outputStream, "outputStream"); 157 requireNonNull(charset, "charset"); 158 var writer = new OutputStreamWriter(outputStream, charset); 159 return new TeeWriter(writer); 160 } 161}