publish json

examples.txt

@@ -44,8 +44,7 @@ Collection Functions
 String Functions
 String Formatting
 Regular Expressions
-Bytes
-# JSON
+JSON
 Time
 Epoch
 # Time Parsing / Formatting

examples/json/json.go

@@ -1,39 +1,119 @@
+// Go offers built-in support for JSON encoding and
+// decoding, including to and from built-in and custom
+// data types.
+
 package main
 
 import "encoding/json"
 import "fmt"
+import "os"
+
+// We'll use these two structs to demonstrate encoding and
+// decoding of custom types below.
+type Response1 struct {
+    Page   int
+    Fruits []string
+}
+type Response2 struct {
+    Page   int      `json:"page"`
+    Fruits []string `json:"fruits"`
+}
 
 func main() {
-    // data to bytes/string
+
+    // First we'll look at encoding basic data types to
+    // JSON strings. Here are some examples for atomic
+    // values.
     bolB, _ := json.Marshal(true)
     fmt.Println(string(bolB))
 
-    numB, _ := json.Marshal(1)
-    fmt.Println(string(numB))
+    intB, _ := json.Marshal(1)
+    fmt.Println(string(intB))
+
+    fltB, _ := json.Marshal(2.34)
+    fmt.Println(string(fltB))
 
     strB, _ := json.Marshal("gopher")
     fmt.Println(string(strB))
 
-    arrD := []string{"apple", "peach", "pear"}
-    arrB, _ := json.Marshal(arrD)
-    fmt.Println(string(arrB))
+    // And here are some for slices and maps, which encode
+    // to JSON arrays and objects as you'd expect.
+    slcD := []string{"apple", "peach", "pear"}
+    slcB, _ := json.Marshal(slcD)
+    fmt.Println(string(slcB))
 
-    hshD := map[string]int{"apple": 5, "lettuce": 7}
-    hshB, _ := json.Marshal(hshD)
-    fmt.Println(string(hshB))
+    mapD := map[string]int{"apple": 5, "lettuce": 7}
+    mapB, _ := json.Marshal(mapD)
+    fmt.Println(string(mapB))
 
-    // string to data
+    // The JSON package can automatically encode your
+    // custom data types. It will only include exported
+    // fields in the encoded output and will by default
+    // use those names as the JSON keys.
+    res1D := &Response1{
+        Page:   1,
+        Fruits: []string{"apple", "peach", "pear"}}
+    res1B, _ := json.Marshal(res1D)
+    fmt.Println(string(res1B))
+
+    // You can use tags on struct field declarations
+    // to customize the encoded JSON key names. Check the
+    // definition of `Response2` above to see an example
+    // of such tags.
+    res2D := &Response2{
+        Page:   1,
+        Fruits: []string{"apple", "peach", "pear"}}
+    res2B, _ := json.Marshal(res2D)
+    fmt.Println(string(res2B))
+
+    // Now let's look at decoding JSON data into Go
+    // values. Here's an example for a generic data
+    // structure. 
     byt := []byte(`{"num":6.0,"strs":["a","b"]}`)
+
+    // We need to provide a variable where the JSON
+    // package can put the decoded data. This
+    // `map[string]interface{}` will hold a map of strings
+    // to arbitrary data types.
     var dat map[string]interface{}
-    err := json.Unmarshal(byt, &dat)
-    if err != nil {
+
+    // Here's the actual decoding, and a check for
+    // associated errors.
+    if err := json.Unmarshal(byt, &dat); err != nil {
         panic(err)
     }
     fmt.Println(dat)
 
+    // In order to use the values in the decoded map,
+    // we'll need to cast them to their appropriate type.
+    // For example here we cast the value in `num` to
+    // the expected `float64` type.
     num := dat["num"].(float64)
     fmt.Println(num)
 
+    // Accessing nested data requires a series of
+    // casts.
     strs := dat["strs"].([]interface{})
-    fmt.Println(strs)
+    str1 := strs[0].(string)
+    fmt.Println(str1)
+
+    // We can also decode JSON into custom data types.
+    // This has the advantages of adding additional
+    // type-safety to our programs and eliminating the
+    // need for type assertions when accessing the decoded
+    // data.
+    str := `{"page": 1, "fruits": ["apple", "peach"]}`
+    res := &Response2{}
+    json.Unmarshal([]byte(str), &res)
+    fmt.Println(res)
+    fmt.Println(res.Fruits[0])
+
+    // In the examples above we always used bytes and
+    // strings as intermediates between the data and
+    // JSON representation on standard out. We can also
+    // stream JSON encodings directly to `os.Writer`s like
+    // `os.Stdout` or even HTTP response bodies.
+    enc := json.NewEncoder(os.Stdout)
+    d := map[string]int{"apple": 5, "lettuce": 7}
+    enc.Encode(d)
 }

examples/json/json.sh

@@ -0,0 +1,21 @@
+$ go run json.go
+true
+1
+2.34
+"gopher"
+["apple","peach","pear"]
+{"apple":5,"lettuce":7}
+{"Page":1,"Fruits":["apple","peach","pear"]}
+{"page":1,"fruits":["apple","peach","pear"]}
+map[num:6 strs:[a b]]
+6
+a
+&{1 [apple peach]}
+apple
+{"apple":5,"lettuce":7}
+
+
+# We've covered the basic of JSON in Go here, but check
+# out the [JSON and Go](http://blog.golang.org/2011/01/json-and-go.html)
+# blog post and [JSON package docs](http://golang.org/pkg/encoding/json/)
+# for more.