IndentingPrintWriter.java revision 71cb446f010e791ca77a27c416a79b5ccb3f075b 
1/*
2 * Copyright (C) 2012 The Android Open Source Project
3 *
4 * Licensed under the Apache License, Version 2.0 (the "License");
5 * you may not use this file except in compliance with the License.
6 * You may obtain a copy of the License at
7 *
8 *      http://www.apache.org/licenses/LICENSE-2.0
9 *
10 * Unless required by applicable law or agreed to in writing, software
11 * distributed under the License is distributed on an "AS IS" BASIS,
12 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
13 * See the License for the specific language governing permissions and
14 * limitations under the License.
15 */
16
17package com.android.internal.util;
18
19import java.io.PrintWriter;
20import java.io.Writer;
21
22/**
23 * Lightweight wrapper around {@link PrintWriter} that automatically indents
24 * newlines based on internal state. It also automatically wraps long lines
25 * based on given line length.
26 * <p>
27 * Delays writing indent until first actual write on a newline, enabling indent
28 * modification after newline.
29 */
30public class IndentingPrintWriter extends PrintWriter {
31    private final String mSingleIndent;
32    private final int mWrapLength;
33
34    /** Mutable version of current indent */
35    private StringBuilder mIndentBuilder = new StringBuilder();
36    /** Cache of current {@link #mIndentBuilder} value */
37    private char[] mCurrentIndent;
38    /** Length of current line being built, excluding any indent */
39    private int mCurrentLength;
40
41    /**
42     * Flag indicating if we're currently sitting on an empty line, and that
43     * next write should be prefixed with the current indent.
44     */
45    private boolean mEmptyLine = true;
46
47    public IndentingPrintWriter(Writer writer, String singleIndent) {
48        this(writer, singleIndent, -1);
49    }
50
51    public IndentingPrintWriter(Writer writer, String singleIndent, int wrapLength) {
52        super(writer);
53        mSingleIndent = singleIndent;
54        mWrapLength = wrapLength;
55    }
56
57    public void increaseIndent() {
58        mIndentBuilder.append(mSingleIndent);
59        mCurrentIndent = null;
60    }
61
62    public void decreaseIndent() {
63        mIndentBuilder.delete(0, mSingleIndent.length());
64        mCurrentIndent = null;
65    }
66
67    public void printPair(String key, Object value) {
68        print(key + "=" + String.valueOf(value) + " ");
69    }
70
71    @Override
72    public void write(char[] buf, int offset, int count) {
73        final int indentLength = mIndentBuilder.length();
74        final int bufferEnd = offset + count;
75        int lineStart = offset;
76        int lineEnd = offset;
77
78        // March through incoming buffer looking for newlines
79        while (lineEnd < bufferEnd) {
80            char ch = buf[lineEnd++];
81            mCurrentLength++;
82            if (ch == '\n') {
83                maybeWriteIndent();
84                super.write(buf, lineStart, lineEnd - lineStart);
85                lineStart = lineEnd;
86                mEmptyLine = true;
87                mCurrentLength = 0;
88            }
89
90            // Wrap if we've pushed beyond line length
91            if (mWrapLength > 0 && mCurrentLength >= mWrapLength - indentLength) {
92                if (!mEmptyLine) {
93                    // Give ourselves a fresh line to work with
94                    super.write('\n');
95                    mEmptyLine = true;
96                    mCurrentLength = lineEnd - lineStart;
97                } else {
98                    // We need more than a dedicated line, slice it hard
99                    maybeWriteIndent();
100                    super.write(buf, lineStart, lineEnd - lineStart);
101                    super.write('\n');
102                    mEmptyLine = true;
103                    lineStart = lineEnd;
104                    mCurrentLength = 0;
105                }
106            }
107        }
108
109        if (lineStart != lineEnd) {
110            maybeWriteIndent();
111            super.write(buf, lineStart, lineEnd - lineStart);
112        }
113    }
114
115    private void maybeWriteIndent() {
116        if (mEmptyLine) {
117            mEmptyLine = false;
118            if (mIndentBuilder.length() != 0) {
119                if (mCurrentIndent == null) {
120                    mCurrentIndent = mIndentBuilder.toString().toCharArray();
121                }
122                super.write(mCurrentIndent, 0, mCurrentIndent.length);
123            }
124        }
125    }
126}
127