Package com.cedarsoftware.io

Class JsonWriter

java.lang.Object
com.cedarsoftware.io.JsonWriter
All Implemented Interfaces:
WriterContext, Closeable, Flushable, AutoCloseable
public class JsonWriter extends Object implements WriterContext, Closeable, Flushable
Output a Java object graph in JSON format. This code handles cyclic references and can serialize any Object graph without requiring a class to be 'Serializable' or have any specific methods on it.
  • Call the static method: JsonWriter.objectToJson(employee). This will convert the passed in 'employee' instance into a JSON String.
  • Using streams: 
         JsonWriter writer = new JsonWriter(stream);
     writer.write(employee);
     writer.close();
    This will write the 'employee' object to the passed in OutputStream.

That's it. This can be used as a debugging tool. Output an object graph using the above code. Use the JsonWriter PRETTY_PRINT option to format the JSON to be human-readable.

This will output any object graph deeply (or null). Object references are properly handled. For example, if you had A->B, B->C, and C->A, then A will be serialized with a B object in it, B will be serialized with a C object in it, and then C will be serialized with a reference to A (ref), not a redefinition of A.


Author:
John DeRegnaucourt ([email protected])
Copyright (c) Cedar Software LLC

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

License

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.

  • Nested Class Summary

    Nested Classes
    Modifier and Type
    Class
    Description
    static interface 
    JsonWriter.JsonClassWriter
    Implement this interface to customize the JSON output for a given class.

  • Constructor Summary

    Constructors
    Constructor
    Description
    JsonWriter(OutputStream out)
     
    JsonWriter(OutputStream out, WriteOptions writeOptions)
     

  • Method Summary

    Modifier and Type
    Method
    Description
    void
    close()
     
    static boolean
    ensureJsonPrimitiveKeys(Map map)
    Ensure that all keys within the Map are String instances
    void
    flush()
     
    protected Map<Object,Long>
    getObjsReferenced()
    Map containing all objects that were referenced within input object graph.
    protected Map<Object,Long>
    getObjVisited()
    Map containing all objects that were visited within input object graph
    WriteOptions
    getWriteOptions()
    Gets the write options for the current serialization
    void
    newLine()
    Add newline (\n) to output
    void
    tabIn()
    Tab the output left (less indented)
    void
    tabOut()
    Tab the output right (more indented)
    protected void
    traceFields(Deque<Object> stack, Object obj)
    Reach-ability trace to visit all objects within the graph to be written.
    protected void
    traceReferences(Object root)
    Walk object graph and visit each instance, following each field, each Collection, Map and so on.
    void
    write(Object obj)
    Write the passed in Java object in JSON format.
    boolean
    writeArrayElementIfMatching(Class<?> arrayComponentClass, Object o, boolean showType, Writer output)
    Write the passed in array element to the JSON output, if any only if, there is a custom writer for the class of the instance 'o'.
    static void
    writeBasicString(Writer writer, String s)
    Writes out a string without special characters.
    protected boolean
    writeCustom(Class<?> arrayComponentClass, Object o, boolean showType, Writer output)
    Perform the actual custom writing for an array element that has a custom writer.
    void
    writeImpl(Object obj, boolean showType)
    Main entry point (mostly used internally, but may be called from a Custom JSON writer).
    static void
    writeJsonUtf8String(Writer output, String s)
    Write out special characters "\b, \f, \t, \n, \r", as such, backslash as \\ quote as \" and values less than an ASCII space (20hex) as "\\u00xx" format, characters in the range of ASCII space to a '~' as ASCII, and anything higher in UTF-8.
    void
    writeObject(Object obj, boolean showType, boolean bodyOnly)
    Allows you to use the current JsonWriter to write an object out.
    boolean
    writeUsingCustomWriter(Object o, boolean showType, Writer output)
    Write the passed in object (o) to the JSON output stream, if and only if, there is a custom writer associated to the Class of object (o).

    Methods inherited from class java.lang.Object

    clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

  • Constructor Details

    • JsonWriter

      public JsonWriter(OutputStream out)
      Parameters:
      out - OutputStream to which the JSON will be written. Uses the default WriteOptions.
      See Also:

    • JsonWriter

      public JsonWriter(OutputStream out, WriteOptions writeOptions)
      Parameters:
      out - OutputStream to which the JSON output will be written.
      writeOptions - WriteOptions containing many feature options to control the JSON output. Can be null, in which case the default WriteOptions will be used.
      See Also:

  • Method Details

    • getWriteOptions

      public WriteOptions getWriteOptions()
      Description copied from interface: WriterContext
      Gets the write options for the current serialization
      Specified by:
      getWriteOptions in interface WriterContext
      Returns:
      WriteOptions

    • getObjVisited

      protected Map<Object,Long> getObjVisited()
      Map containing all objects that were visited within input object graph

    • getObjsReferenced

      protected Map<Object,Long> getObjsReferenced()
      Map containing all objects that were referenced within input object graph.

    • tabIn

      public void tabIn() throws IOException
      Tab the output left (less indented)
      Throws:
      IOException

    • newLine

      public void newLine() throws IOException
      Add newline (\n) to output
      Throws:
      IOException

    • tabOut

      public void tabOut() throws IOException
      Tab the output right (more indented)
      Throws:
      IOException

    • writeUsingCustomWriter

      public boolean writeUsingCustomWriter(Object o, boolean showType, Writer output)
      Write the passed in object (o) to the JSON output stream, if and only if, there is a custom writer associated to the Class of object (o).
      Parameters:
      o - Object to be (potentially written)
      showType - boolean indicating whether to show @type.
      output - Writer where the actual JSON is being written to.
      Returns:
      boolean true if written, false is there is no custom writer for the passed in object.

    • writeArrayElementIfMatching

      public boolean writeArrayElementIfMatching(Class<?> arrayComponentClass, Object o, boolean showType, Writer output)
      Write the passed in array element to the JSON output, if any only if, there is a custom writer for the class of the instance 'o'.
      Parameters:
      arrayComponentClass - Class type of the array
      o - Object instance to write
      showType - boolean indicating whether @type should be output.
      output - Writer to write the JSON to (if there is a custom writer for o's Class).
      Returns:
      true if the array element was written, false otherwise.

    • writeCustom

      protected boolean writeCustom(Class<?> arrayComponentClass, Object o, boolean showType, Writer output) throws IOException
      Perform the actual custom writing for an array element that has a custom writer.
      Parameters:
      arrayComponentClass - Class type of the array
      o - Object instance to write
      showType - boolean indicating whether @type should be output.
      output - Writer to write the JSON to (if there is a custom writer for o's Class).
      Returns:
      true if the array element was written, false otherwise.
      Throws:
      IOException

    • write

      public void write(Object obj)
      Write the passed in Java object in JSON format.
      Parameters:
      obj - Object any Java Object or JsonObject.

    • traceReferences

      protected void traceReferences(Object root)
      Walk object graph and visit each instance, following each field, each Collection, Map and so on. Tracks visited to handle cycles and to determine if an item is referenced elsewhere. If an object is never referenced more than once, no @id field needs to be emitted for it.
      Parameters:
      root - Object to be deeply traced. The objVisited and objsReferenced Maps will be written to during the trace.

    • traceFields

      protected void traceFields(Deque<Object> stack, Object obj)
      Reach-ability trace to visit all objects within the graph to be written. This API will handle any object, using either reflection APIs or by consulting a specified includedFields map if provided.
      Parameters:
      stack - Deque used to manage descent into graph (rather than using Java stack.) This allows for much larger graph processing.
      obj - Object root of graph the JDK reflection operations. This allows a subset of the actual fields on an object to be serialized.

    • writeImpl

      public void writeImpl(Object obj, boolean showType) throws IOException
      Main entry point (mostly used internally, but may be called from a Custom JSON writer). This method will write out whatever object type it is given, including JsonObject's. It will handle null, detecting if a custom writer should be called, array, array of JsonObject, Map, Map of JsonObjects, Collection, Collection of JsonObject, any regular object, or a JsonObject representing a regular object.
      Parameters:
      obj - Object to be written
      showType - if set to true, the @type tag will be output. If false, it will be
      Throws:
      IOException - if one occurs on the underlying output stream.

    • ensureJsonPrimitiveKeys

      public static boolean ensureJsonPrimitiveKeys(Map map)
      Ensure that all keys within the Map are String instances
      Parameters:
      map - Map to inspect that all keys are primitive. This allows the output JSON to be optimized into {"key1":value1, "key2": value2} format if all the keys of the Map are Strings. If not, then a Map is written as two arrays, a @keys array and an @items array. This allows support for Maps with non-String keys.

    • writeObject

      public void writeObject(Object obj, boolean showType, boolean bodyOnly) throws IOException
      Description copied from interface: WriterContext
      Allows you to use the current JsonWriter to write an object out.
      Specified by:
      writeObject in interface WriterContext
      Parameters:
      obj - Object to be written in JSON format
      showType - boolean true means show the "@type" field, false eliminates it. Many times the type can be dropped because it can be inferred from the field or array type.
      bodyOnly - write only the body of the object
      Throws:
      IOException - if an error occurs writing to the output stream.

    • flush

      public void flush()
      Specified by:
      flush in interface Flushable

    • close

      public void close()
      Specified by:
      close in interface AutoCloseable
      Specified by:
      close in interface Closeable

    • writeBasicString

      public static void writeBasicString(Writer writer, String s) throws IOException
      Writes out a string without special characters. Use for labels, etc. when you know you will not need extra formattting for UTF-8 or tabs, quotes and newlines in the string
      Parameters:
      writer - Writer to which the UTF-8 string will be written to
      s - String to be written in UTF-8 format on the output stream.
      Throws:
      IOException - if an error occurs writing to the output stream.

    • writeJsonUtf8String

      public static void writeJsonUtf8String(Writer output, String s) throws IOException
      Write out special characters "\b, \f, \t, \n, \r", as such, backslash as \\ quote as \" and values less than an ASCII space (20hex) as "\\u00xx" format, characters in the range of ASCII space to a '~' as ASCII, and anything higher in UTF-8.
      Parameters:
      output - Writer to which the UTF-8 string will be written to
      s - String to be written in UTF-8 format on the output stream.
      Throws:
      IOException - if an error occurs writing to the output stream.