From 439fe1882bb11a5c318bac07451ab5325755876f Mon Sep 17 00:00:00 2001
From: Magesh Umasankar <umagesh@apache.org>
Date: Mon, 18 Feb 2002 00:59:43 +0000
Subject: [PATCH] Filter to read the first 'n' lines.

git-svn-id: https://svn.apache.org/repos/asf/ant/core/trunk@271391 13f79535-47bb-0310-9956-ffa450edef68
---
 .../apache/tools/ant/filters/HeadFilter.java  | 123 ++++++++++++++++++
 1 file changed, 123 insertions(+)
 create mode 100644 proposal/sandbox/filterreaders/src/main/org/apache/tools/ant/filters/HeadFilter.java

diff --git a/proposal/sandbox/filterreaders/src/main/org/apache/tools/ant/filters/HeadFilter.java b/proposal/sandbox/filterreaders/src/main/org/apache/tools/ant/filters/HeadFilter.java
new file mode 100644
index 000000000..3d72a3ffa
--- /dev/null
+++ b/proposal/sandbox/filterreaders/src/main/org/apache/tools/ant/filters/HeadFilter.java
@@ -0,0 +1,123 @@
+package org.apache.tools.ant.filters;
+
+import java.io.FilterReader;
+import java.io.IOException;
+import java.io.Reader;
+
+import org.apache.tools.ant.types.Parameter;
+import org.apache.tools.ant.types.Parameterizable;
+
+/**
+ * Read the first n lines (Default is first 10 lines)
+ *
+ * Example:
+ * =======
+ *
+ * <filterreader classname="org.apache.tools.ant.filters.HeadFilter">
+ *    <param name="lines" value="3"/>
+ * </filterreader>
+ *
+ * @author <a href="mailto:umagesh@apache.org">Magesh Umasankar</a>
+ */
+public final class HeadFilter
+    extends FilterReader
+    implements Parameterizable
+{
+    private static final String LINES_KEY = "lines";
+
+    private Parameter[] parameters;
+
+    private boolean initialized = false;
+
+    private long linesRead = 0;
+
+    private long lines = 10;
+
+    private boolean ignoreLineFeed = false;
+
+    /**
+     * Create a new filtered reader.
+     *
+     * @param in  a Reader object providing the underlying stream.
+     */
+    public HeadFilter(final Reader in) {
+        super(in);
+    }
+
+    public final int read() throws IOException {
+        if (!initialized) {
+            initialize();
+            initialized = true;
+        }
+
+        int ch = -1;
+
+        if (linesRead < lines) {
+
+            ch = in.read();
+
+            if (ignoreLineFeed) {
+                if (ch == '\n') {
+                    ch = in.read();
+                }
+                ignoreLineFeed = false;
+            }
+
+            switch (ch) {
+                case '\r':
+                    ch = '\n';
+                    ignoreLineFeed = true;
+                    //fall through
+                case '\n':
+                    linesRead++;
+                    break;
+            }
+        }
+
+        return ch;
+    }
+
+    public final int read(final char cbuf[], final int off,
+                          final int len) throws IOException {
+        for (int i = 0; i < len; i++) {
+            final int ch = read();
+            if (ch == -1) {
+                if (i == 0) {
+                    return -1;
+                } else {
+                    return i;
+                }
+            }
+            cbuf[off + i] = (char) ch;
+        }
+        return len;
+    }
+
+    public final long skip(long n) throws IOException {
+        for (long i = 0; i < n; i++) {
+            if (in.read() == -1) {
+                return i;
+            }
+        }
+        return n;
+    }
+
+    /**
+     * Set Parameters
+     */
+    public final void setParameters(final Parameter[] parameters) {
+        this.parameters = parameters;
+        initialized = false;
+    }
+
+    private final void initialize() {
+        if (parameters != null) {
+            for (int i = 0; i < parameters.length; i++) {
+                if (LINES_KEY.equals(parameters[i].getName())) {
+                    lines = new Long(parameters[i].getValue()).longValue();
+                    break;
+                }
+            }
+        }
+    }
+}