Alternate approach for issue #17

src/main/java/com/fasterxml/jackson/core/JsonGenerator.java

@@ -4,7 +4,9 @@
  */
 package com.fasterxml.jackson.core;
 
-import static com.fasterxml.jackson.core.JsonTokenId.*;
+import com.fasterxml.jackson.core.JsonParser.NumberType;
+import com.fasterxml.jackson.core.io.CharacterEscapes;
+import com.fasterxml.jackson.core.util.VersionUtil;
 
 import java.io.*;
 import java.math.BigDecimal;
@@ -13,9 +15,7 @@
 import java.util.concurrent.atomic.AtomicInteger;
 import java.util.concurrent.atomic.AtomicLong;
 
-import com.fasterxml.jackson.core.JsonParser.NumberType;
-import com.fasterxml.jackson.core.io.CharacterEscapes;
-import com.fasterxml.jackson.core.util.VersionUtil;
+import static com.fasterxml.jackson.core.JsonTokenId.*;
 
 /**
  * Base class that defines public API for writing JSON content.
@@ -932,6 +932,18 @@ public void writeArray(double[] array, int offset, int length) throws IOExceptio
      */
     public abstract void writeString(String text) throws IOException;
 
+    /**
+     * Method for outputting a String value. Depending on context
+     * this means either array element, (object) field value or
+     * a stand alone String; but in all cases, String will be
+     * surrounded in double quotes, and contents will be properly
+     * escaped as required by JSON specification.
+     * If the reader is null, then write a null.
+     * If len is < 0, then write all contents of the reader.
+     * Otherwise, write only len characters.
+     */
+    public abstract void writeString(Reader reader, int len) throws IOException;
+
     /**
      * Method for outputting a String value. Depending on context
      * this means either array element, (object) field value or

src/main/java/com/fasterxml/jackson/core/base/GeneratorBase.java

@@ -1,14 +1,16 @@
 package com.fasterxml.jackson.core.base;
 
-import java.io.*;
-import java.math.BigDecimal;
-
 import com.fasterxml.jackson.core.*;
 import com.fasterxml.jackson.core.json.DupDetector;
 import com.fasterxml.jackson.core.json.JsonWriteContext;
 import com.fasterxml.jackson.core.json.PackageVersion;
 import com.fasterxml.jackson.core.util.DefaultPrettyPrinter;
 
+import java.io.IOException;
+import java.io.InputStream;
+import java.io.Reader;
+import java.math.BigDecimal;
+
 /**
  * This base class implements part of API that a JSON generator exposes
  * to applications, adds shared internal methods that sub-classes
@@ -339,6 +341,12 @@ public int writeBinary(Base64Variant b64variant, InputStream data, int dataLengt
         return 0;
     }
 
+    @Override
+    public void writeString(Reader reader, int len) throws IOException {
+        // Let's implement this as "unsupported" to make it easier to add new parser impls
+        _reportUnsupportedOperation();
+    }
+
     /*
    /**********************************************************
    /* Public API, write methods, primitive

src/main/java/com/fasterxml/jackson/core/json/UTF8JsonGenerator.java

@@ -1,12 +1,18 @@
 package com.fasterxml.jackson.core.json;
 
-import java.io.*;
+import com.fasterxml.jackson.core.*;
+import com.fasterxml.jackson.core.io.CharTypes;
+import com.fasterxml.jackson.core.io.CharacterEscapes;
+import com.fasterxml.jackson.core.io.IOContext;
+import com.fasterxml.jackson.core.io.NumberOutput;
+
+import java.io.IOException;
+import java.io.InputStream;
+import java.io.OutputStream;
+import java.io.Reader;
 import java.math.BigDecimal;
 import java.math.BigInteger;
 
-import com.fasterxml.jackson.core.*;
-import com.fasterxml.jackson.core.io.*;
-
 public class UTF8JsonGenerator
     extends JsonGeneratorImpl
 {
@@ -461,6 +467,54 @@ public void writeString(String text) throws IOException
         _outputBuffer[_outputTail++] = _quoteChar;
     }
 
+    @Override
+    public void writeString(Reader reader, int len) throws IOException {
+        _verifyValueWrite(WRITE_STRING);
+        if (reader == null) {
+            _reportError("null reader");
+        }
+
+        int toRead = (len >= 0) ? len : Integer.MAX_VALUE;
+
+        //TODO: Check that this use is OK
+        final char[] buf = _charBuffer;
+
+        //Add leading quote
+        if ((_outputTail + len) >= _outputEnd) {
+            _flushBuffer();
+        }
+        _outputBuffer[_outputTail++] = _quoteChar;
+
+        //read
+        while(toRead > 0){
+            int toReadNow = Math.min(toRead, buf.length);
+            if(toRead <= 0){
+                break;
+            }
+            int numRead = reader.read(buf, 0, toReadNow);
+            if(numRead <= 0){
+                break;
+            }
+            if ((_outputTail + len) >= _outputEnd) {
+                _flushBuffer();
+            }
+            _writeStringSegments(buf, 0, numRead);
+
+            //decrease tracker
+            toRead -= numRead;
+        }
+
+        //Add trailing quote
+        if ((_outputTail + len) >= _outputEnd) {
+            _flushBuffer();
+        }
+        _outputBuffer[_outputTail++] = _quoteChar;
+
+        if(toRead > 0 && len >= 0){
+            _reportError("Didn't read enough from reader");
+        }
+    }
+
     @Override
     public void writeString(char[] text, int offset, int len) throws IOException
     {

src/main/java/com/fasterxml/jackson/core/json/WriterBasedJsonGenerator.java

@@ -1,12 +1,18 @@
 package com.fasterxml.jackson.core.json;
 
-import java.io.*;
+import com.fasterxml.jackson.core.*;
+import com.fasterxml.jackson.core.io.CharTypes;
+import com.fasterxml.jackson.core.io.CharacterEscapes;
+import com.fasterxml.jackson.core.io.IOContext;
+import com.fasterxml.jackson.core.io.NumberOutput;
+
+import java.io.IOException;
+import java.io.InputStream;
+import java.io.Reader;
+import java.io.Writer;
 import java.math.BigDecimal;
 import java.math.BigInteger;
 
-import com.fasterxml.jackson.core.*;
-import com.fasterxml.jackson.core.io.*;
-
 /**
  * {@link JsonGenerator} that outputs JSON content using a {@link java.io.Writer}
  * which handles character encoding.
@@ -69,6 +75,17 @@ public class WriterBasedJsonGenerator
      */
     protected char[] _entityBuffer;
 
+    /**
+     * Intermediate buffer in which characters of a String are copied
+     * before being encoded.
+     */
+    protected char[] _charBuffer;
+
+    /**
+     * Length of <code>_charBuffer</code>
+     */
+    protected final int _charBufferLength;
+
     /**
      * When custom escapes are used, this member variable is used
      * internally to hold a reference to currently used escape
@@ -88,6 +105,8 @@ public WriterBasedJsonGenerator(IOContext ctxt, int features,
         _writer = w;
         _outputBuffer = ctxt.allocConcatBuffer();
         _outputEnd = _outputBuffer.length;
+        _charBuffer = new char[_outputBuffer.length];
+        _charBufferLength = _charBuffer.length;
     }
 
     /*
@@ -371,6 +390,54 @@ public void writeString(String text) throws IOException
         _outputBuffer[_outputTail++] = _quoteChar;
     }
 
+    @Override
+    public void writeString(Reader reader, int len) throws IOException {
+        _verifyValueWrite(WRITE_STRING);
+        if (reader == null) {
+            _reportError("null reader");
+        } else {
+            int toRead = (len >= 0) ? len : Integer.MAX_VALUE;
+
+            //TODO: Check that this use is OK
+            final char[] buf = _charBuffer;
+
+            //Add leading quote
+            if ((_outputTail + len) >= _outputEnd) {
+                _flushBuffer();
+            }
+            _outputBuffer[_outputTail++] = _quoteChar;
+
+            //read
+            while (toRead > 0) {
+                int toReadNow = Math.min(toRead, buf.length);
+                if (toRead <= 0) {
+                    break;
+                }
+                int numRead = reader.read(buf, 0, toReadNow);
+                if (numRead <= 0) {
+                    break;
+                }
+                if ((_outputTail + len) >= _outputEnd) {
+                    _flushBuffer();
+                }
+                _writeString(buf, 0, numRead);
+
+                //decrease tracker
+                toRead -= numRead;
+            }
+
+            //Add trailing quote
+            if ((_outputTail + len) >= _outputEnd) {
+                _flushBuffer();
+            }
+            _outputBuffer[_outputTail++] = _quoteChar;
+
+            if (toRead > 0 && len >= 0) {
+                _reportError("Didn't read enough from reader");
+            }
+        }
+    }
+
     @Override
     public void writeString(char[] text, int offset, int len) throws IOException
     {
@@ -890,6 +957,7 @@ protected void _releaseBuffers()
             _outputBuffer = null;
             _ioContext.releaseConcatBuffer(buf);
         }
+        _charBuffer = null;
     }
 
     /*

src/main/java/com/fasterxml/jackson/core/util/JsonGeneratorDelegate.java

@@ -1,13 +1,14 @@
 package com.fasterxml.jackson.core.util;
 
+import com.fasterxml.jackson.core.*;
+import com.fasterxml.jackson.core.io.CharacterEscapes;
+
 import java.io.IOException;
 import java.io.InputStream;
+import java.io.Reader;
 import java.math.BigDecimal;
 import java.math.BigInteger;
 
-import com.fasterxml.jackson.core.*;
-import com.fasterxml.jackson.core.io.CharacterEscapes;
-
 public class JsonGeneratorDelegate extends JsonGenerator
 {
     /**
@@ -246,6 +247,11 @@ public void writeArray(double[] array, int offset, int length) throws IOExceptio
     @Override
     public void writeString(String text) throws IOException { delegate.writeString(text); }
 
+    @Override
+    public void writeString(Reader reader, int len) throws IOException {
+        delegate.writeString(reader, len);
+    }
+
     @Override
     public void writeString(char[] text, int offset, int len) throws IOException { delegate.writeString(text, offset, len); }